VALGRIND(1)

📦

version 3.27.1 · 7 versions

💅 valgrind(1) — bestie edition 💅

okay so listen. valgrind is literally the moment. no cap. it's a whole suite of tools for debugging and profiling programs, and i'm gonna walk you through it like we're texting at 2am. grab a strawberry drink 🍓 and let's go.

✨ NAME ✨

valgrind — a suite of tools for debugging and profiling programs 🦋

✨ SYNOPSIS ✨

valgrind [valgrind-options] [your-program] [your-program-options]

✨ DESCRIPTION ✨

So. Valgrind is a flexible program for debugging and profiling Linux executables. It consists of a core, which provides a synthetic CPU in software, and a series of debugging and profiling tools. The architecture is modular, so that new tools can be created easily and without disturbing the existing structure. iconic behavior honestly 👑

Some of the options described below work with all Valgrind tools, and some only work with a few or one. The section MEMCHECK OPTIONS and those below it describe tool-specific options. iykyk.

This manual page covers only basic usage and options. For more comprehensive information, please see the HTML documentation on your system: $INSTALL/share/doc/valgrind/html/index.html, or online: http://www.valgrind.org/docs/manual/index.html. go read it, it's giving encyclopedia energy 💖

🎀 TOOL SELECTION OPTIONS 🎀

The single most important option. periodt.

--tool=<toolname> [default: memcheck] — Run the Valgrind tool called toolname, e.g. memcheck, cachegrind, callgrind, helgrind, drd, massif, dhat, lackey, none, exp-bbv, etc. choose your fighter 💅

🌈 BASIC OPTIONS 🌈

These options work with all tools. universal besties fr fr.

-h, --help — Show help for all options, both for the core and for the selected tool. If the option is repeated it is equivalent to giving --help-debug. the way that repeating it unlocks secrets 😭
--help-debug — Same as --help, but also lists debugging options which usually are only of use to Valgrind's developers. dev mode activated 🔥
--version — Show the version number of the Valgrind core. Tools can have their own version numbers. There is a scheme in place to ensure that tools only execute when the core version is one they are known to work with. This was done to minimise the chances of strange problems arising from tool-vs-core version incompatibilities. compatibility check, slay 🫶
-q, --quiet — Run silently, and only print error messages. Useful if you are running regression tests or have some other automated test machinery. no thoughts, just errors 💀
-v, --verbose — Be more verbose. Gives extra information on various aspects of your program, such as: the shared objects loaded, the suppressions used, the progress of the instrumentation and execution engines, and warnings about unusual behaviour. Repeating the option increases the verbosity level. the way that more -v means more lore 👑
--trace-children=<yes|no> [default: no] — When enabled, Valgrind will trace into sub-processes initiated via the exec system call. This is necessary for multi-process programs.

Note that Valgrind does trace into the child of a fork (it would be difficult not to, since fork makes an identical copy of a process), so this option is arguably badly named. However, most children of fork calls immediately call exec anyway. awkward naming era but we move 🦋

--trace-children-skip=patt1,patt2,... — This option only has an effect when --trace-children=yes is specified. It allows for some children to be skipped. The option takes a comma separated list of patterns for the names of child executables that Valgrind should not trace into. Patterns may include the metacharacters ? and *, which have the usual meaning.

This can be useful for pruning uninteresting branches from a tree of processes being run on Valgrind. But you should be careful when using it. When Valgrind skips tracing into an executable, it doesn't just skip tracing that executable, it also skips tracing any of that executable's child processes. In other words, the flag doesn't merely cause tracing to stop at the specified executables -- it skips tracing of entire process subtrees rooted at any of the specified executables. no cap, this one's sneaky 👀

--trace-children-skip-by-arg=patt1,patt2,... — This is the same as --trace-children-skip, with one difference: the decision as to whether to trace into a child process is made by examining the arguments to the child process, rather than the name of its executable. plot twist 🌪️
--child-silent-after-fork=<yes|no> [default: no] — When enabled, Valgrind will not show any debugging or logging output for the child process resulting from a fork call. This can make the output less confusing (although more misleading) when dealing with processes that create children. It is particularly useful in conjunction with --trace-children=. Use of this option is also strongly recommended if you are requesting XML output (--xml=yes), since otherwise the XML from child and parent may become mixed up, which usually makes it useless. mixing XML is the villain origin story 😭
--vgdb=<no|yes|full> [default: yes] — Valgrind will provide "gdbserver" functionality when --vgdb=yes or --vgdb=full is specified. This allows an external GNU GDB debugger to control and debug your program when it runs on Valgrind. --vgdb=full incurs significant performance overheads, but provides more precise breakpoints and watchpoints. See Debugging your program using Valgrind's gdbserver and GDB for a detailed description.

If the embedded gdbserver is enabled but no gdb is currently being used, the vgdb command line utility can send "monitor commands" to Valgrind from a shell. The Valgrind core provides a set of Valgrind monitor commands. A tool can optionally provide tool specific monitor commands, which are documented in the tool specific chapter. debug bestie activated 💜

--vgdb-error=<number> [default: 999999999] — Use this option when the Valgrind gdbserver is enabled with --vgdb=yes or --vgdb=full. Tools that report errors will wait for number errors to be reported before freezing the program and waiting for you to connect with GDB. It follows that a value of zero will cause the gdbserver to be started before your program is executed. This is typically used to insert GDB breakpoints before execution, and also works with tools that do not report errors, such as Massif. zero means jump straight in, no waiting 💅
--vgdb-stop-at=<set> [default: none] — Use this option when the Valgrind gdbserver is enabled with --vgdb=yes or --vgdb=full. The Valgrind gdbserver will be invoked for each error after --vgdb-error have been reported. You can additionally ask the Valgrind gdbserver to be invoked for other events, specified in one of the following ways:
- a comma separated list of one or more of startup exit abexit valgrindabexit.

The values startup exit valgrindabexit respectively indicate to invoke gdbserver before your program is executed, after the last instruction of your program, on Valgrind abnormal exit (e.g. internal error, out of memory, ...).

The option abexit is similar to exit but tells to invoke gdbserver only when your application exits abnormally (i.e. with an exit code different of 0).

Note: startup and --vgdb-error=0 will both cause Valgrind gdbserver to be invoked before your program is executed. The --vgdb-error=0 will in addition cause your program to stop on all subsequent errors.

all to specify the complete set. It is equivalent to --vgdb-stop-at=startup,exit,abexit,valgrindabexit.
none for the empty set.

--track-fds=<yes|no|all|bad> [default: no] — When enabled, Valgrind will track all file descriptor usage. It will produce errors for bad file descriptor usage like closing a file descriptor twice, using a file descriptor (number) that was never created, or passing an already closed file descriptor to a system call. It will also print out a list of open file descriptors on exit. Or on request, via the gdbserver monitor command v.info open_fds.

When an error is generated, or when listing the still open file descriptors at exit, a stack backtrace of where the file was opened is printed. If the file descriptor has already been closed, it will also include a backtrace of where it was previously closed. Any error will include details relating to the file descriptor such as the file name or socket details.

Use all to also include reporting on stdin, stdout and stderr (or other inherited file descriptors) at exit. If bad option is used, then exclude reporting on leaked file descriptors at exit and only produce errors about bad file decriptors usage. keep an eye on your fds bestie 👀

--modify-fds=<no|yes|high> [default: no] — When enabled, when the program opens a new file descriptor, the highest available file descriptor is returned instead of the lowest one. Use yes to restrict the feature from the 0/1/2 file descriptors as they're often used for stdout/stderr redirection. reverse uno card energy 🎀
--time-stamp=<yes|no> [default: no] — When enabled, each message is preceded with an indication of the elapsed wallclock time since startup, expressed as days, hours, minutes, seconds and milliseconds. timestamps are the receipts ⏰
--log-fd=<number> [default: 2, stderr] — Specifies that Valgrind should send all of its messages to the specified file descriptor. The default, 2, is the standard error channel (stderr). Note that this may interfere with the client's own use of stderr, as Valgrind's output will be interleaved with any output that the client sends to stderr. sharing stderr is giving chaotic roommate 🫠
--log-file=<filename> — Specifies that Valgrind should send all of its messages to the specified file. If the file name is empty, it causes an abort. There are three special format specifiers that can be used in the file name.

%p is replaced with the current process ID. This is very useful for program that invoke multiple processes. WARNING: If you use --trace-children=yes and your program invokes multiple processes OR your program forks without calling exec afterwards, and you don't use this specifier (or the %q specifier below), the Valgrind output from all those processes will go into one file, possibly jumbled up, and possibly incomplete. Note: If the program forks and calls exec afterwards, Valgrind output of the child from the period between fork and exec will be lost. Fortunately this gap is really tiny for most programs; and modern programs use posix_spawn anyway. 😭

%n is replaced with a file sequence number unique for this process. This is useful for processes that produces several files from the same filename template. cute little counter fr fr 🍓

bestie we're only at part 1 of 14 and i have so much more to tell you. stay tuned, the lore continues 💖 don't go anywhere.

%q{FOO} gets swapped out for the actual contents of the environment variable FOO. If the {FOO} part is malformed, it causes an abort. 💀 This specifier is rarely needed, but very useful in certain circumstances (eg. when running MPI programs). The idea is that you specify a variable which will be set differently for each process in the job — for example BPROC_RANK or whatever is applicable in your MPI setup. And if the named environment variable isn't set, it causes an abort. 🫠 Note that in some shells, the { and } characters may need to be escaped with a backslash.

%% gets replaced with %. That's it, that's the whole thing. 💅

If an % is followed by any other character, it causes an abort. Any other character. No exceptions.

If the file name specifies a relative file name, it's put in the program's initial working directory — meaning the current directory when the program started its execution after the fork or after the exec. If it specifies an absolute file name (ie. starts with /) then it's put there. ✨

--log-socket=<ip-address:port-number> — tells Valgrind to send all of its messages to the specified port at the specified IP address. The port may be omitted, in which case port 1500 is used. If a connection cannot be made to the specified socket, Valgrind falls back to writing output to the standard error (stderr). This option is intended to be used in conjunction with the valgrind-listener program. For further details, see the commentary in the manual. 🎧
--enable-debuginfod=<no|yes> [default: yes] — when enabled, Valgrind will attempt to download missing debuginfo from debuginfod servers if space-separated server URLs are present in the $DEBUGINFOD_URLS environment variable. This option is supported on Linux only, bestie. 🐧

These options are used by all tools that can report errors, e.g. Memcheck, but not Cachegrind. K.

--xml=<yes|no> [default: no] — when enabled, the important parts of the output (e.g. tool error messages) will be in XML format rather than plain text. Furthermore, the XML output will be sent to a different output channel than the plain text output. Therefore, you also must use one of --xml-fd, --xml-file or --xml-socket to specify where the XML is to be sent.

Less important messages will still be printed in plain text, but because the XML output and plain text output are sent to different output channels (the destination of the plain text output is still controlled by --log-fd, --log-file and --log-socket) this should not cause problems.

This option is aimed at making life easier for tools that consume Valgrind's output as input, such as GUI front ends. Currently this option works with Memcheck, Helgrind and DRD. The output format is specified in the file docs/internals/xml-output-protocol4.txt in the source tree for Valgrind 3.5.0 or later.

The recommended options for a GUI to pass, when requesting XML output, are: --xml=yes to enable XML output, --xml-file to send the XML output to a (presumably GUI-selected) file, --log-file to send the plain text output to a second GUI-selected file, --child-silent-after-fork=yes, and -q to restrict the plain text output to critical error messages created by Valgrind itself. For example, failure to read a specified suppressions file counts as a critical error message. In this way, for a successful run the text output file will be empty. But if it isn't empty, then it will contain important information which the GUI user should be made aware of. 👑

--xml-fd=<number> [default: -1, disabled] — tells Valgrind to send its XML output to the specified file descriptor. It must be used in conjunction with --xml=yes.
--xml-file=<filename> — tells Valgrind to send its XML output to the specified file. It must be used in conjunction with --xml=yes. Any %p or %q sequences appearing in the filename are expanded in exactly the same way as they are for --log-file. See the description of --log-file for details. 📄
--xml-socket=<ip-address:port-number> — tells Valgrind to send its XML output to the specified port at the specified IP address. It must be used in conjunction with --xml=yes. The form of the argument is the same as that used by --log-socket. See the description of --log-socket for further details.
--xml-user-comment=<string> — embeds an extra user comment string at the start of the XML output. Only works when --xml=yes is specified; ignored otherwise.
--demangle=<yes|no> [default: yes] — enable/disable automatic demangling (decoding) of C++, D, Rust, Java, Ada names. Enabled by default. When enabled, Valgrind will attempt to translate encoded names in the listed languages back to something approaching the original. Note that the callgrind tool always disables Ada demangling in order to differentiate overloaded functions and procedures in the callgraph. The demangler handles symbols mangled by g++ versions 2.X, 3.X and 4.X.

An important fact about demangling is that function names mentioned in suppressions files should be in their mangled form. Valgrind does not demangle function names when searching for applicable suppressions, because to do otherwise would make suppression file contents dependent on the state of Valgrind's demangling machinery, and also slow down suppression matching. 🧠

--num-callers=<number> [default: 12] — specifies the maximum number of entries shown in stack traces that identify program locations. Note that errors are commoned up using only the top four function locations (the place in the current function, and that of its three immediate callers). So this doesn't affect the total number of errors reported.

The maximum value for this is 500. Note that higher settings will make Valgrind run a bit more slowly and take a bit more memory, but can be useful when working with programs with deeply-nested call chains.

The minimum value for this is 2. A value of 1 is not allowed for two reasons. Firstly, some of the default suppressions use "..." which is forbidden with --num-callers=1. Secondly, it would make leak suppressions match all allocations using the allocation function (e.g., malloc).

--unw-stack-scan-thresh=<number> [default: 0], --unw-stack-scan-frames=<number> [default: 5] — stack-scanning support is available only on ARM targets. 🦾

These flags enable and control stack unwinding by stack scanning. When the normal stack unwinding mechanisms — usage of Dwarf CFI records, and frame-pointer following — fail, stack scanning may be able to recover a stack trace.

Note that stack scanning is an imprecise, heuristic mechanism that may give very misleading results, or none at all. It should be used only in emergencies, when normal unwinding fails, and it is important to nevertheless have stack traces.

Stack scanning is a simple technique: the unwinder reads words from the stack, and tries to guess which of them might be return addresses, by checking to see if they point just after ARM or Thumb call instructions. If so, the word is added to the backtrace.

The main danger occurs when a function call returns, leaving its return address exposed, and a new function is called, but the new function does not overwrite the old address. The result of this is that the backtrace may contain entries for functions which have already returned, and so be very confusing. 😭

A second limitation of this implementation is that it will scan only the page (4KB, normally) containing the starting stack pointer. If the stack frames are large, this may result in only a few (or not even any) being present in the trace. Also, if you are unlucky and have an initial stack pointer near the end of its containing page, the scan may miss all interesting frames.

By default stack scanning is disabled. The normal use case is to ask for it when a stack trace would otherwise be very short. So, to enable it, use --unw-stack-scan-thresh=number. This requests Valgrind to try using stack scanning to "extend" stack traces which contain fewer than number frames.

If stack scanning does take place, it will only generate at most the number of frames specified by --unw-stack-scan-frames. Typically, stack scanning generates so many garbage entries that this value is set to a low value (5) by default. In no case will a stack trace larger than the value specified by --num-callers be created.

--error-limit=<yes|no> [default: yes] — when enabled, Valgrind stops reporting errors after 10,000,000 in total, or 1,000 different ones, have been seen. This is to stop the error tracking machinery from becoming a huge performance overhead in programs with many errors. 🛑
--error-exitcode=<number> [default: 0] — specifies an alternative exit code to return if Valgrind reported any errors in the run. When set to the default value (zero), the return value from Valgrind will always be the return value of the process being simulated. When set to a nonzero value, that value is returned instead, if Valgrind detects any errors. This is useful for using Valgrind as part of an automated test suite, since it makes it easy to detect test cases for which Valgrind has reported errors, just by inspecting return codes. When set to a nonzero value and Valgrind detects no error, the return value of Valgrind will be the return value of the program being simulated.
--exit-on-first-error=<yes|no> [default: no] — if this option is enabled, Valgrind exits on the first error. A nonzero exit value must be defined using the --error-exitcode option. Useful if you are running regression tests or have some other automated test machinery. 🏃‍♀️
--error-markers=<begin>,<end> [default: none] — when errors are output as plain text (i.e. XML not used), --error-markers instructs Valgrind to output a line containing the begin (end) string before (after) each error.

Such marker lines facilitate searching for errors and/or extracting errors in an output file that contain valgrind errors mixed with the program output.

Note that empty markers are accepted. So, only using a begin (or an end) marker is possible. ✂️

--show-error-list=no|yes|all [default: no] — okay so bestie, if you set this to yes, then for all the tools that actually report errors, Valgrind will drop the list of detected errors and the list of used suppressions on you at exit. 💅 And if you set it to all? It also shows you the list of suppressed errors. Iconic.

heads up: at verbosity 2 and above, Valgrind automatically shows you the detected-errors list and the used-suppressions list at exit anyway — unless you explicitly picked --show-error-list=no. So it's giving "opt out", not "opt in".

-s — shorthand, bestie. Typing -s is literally the same thing as --show-error-list=yes. ✨
--sigill-diagnostics=<yes|no> [default: yes] — turn the illegal-instruction diagnostics on or off. On by default, BUT it flips to disabled when you pass --quiet. And the default can always be overridden explicitly by just handing it this option, no cap.

When it's enabled, you get a warning message plus some diagnostics whenever Valgrind hits an instruction it can't decode or translate — and this happens before the program gets a SIGILL signal. Usually an illegal instruction means either there's a bug in the program or Valgrind just doesn't support that particular instruction yet. 🌸 But some programs deliberately try to execute an instruction that might be missing, and then trap the SIGILL to sniff out processor features. Using this flag lets you dodge all that diagnostic output you'd otherwise be drowning in for those cases. 🫶

--keep-debuginfo=<yes|no> [default: no] — when you turn this on, Valgrind keeps ("archives") symbols and all other debuginfo for code that's been unloaded. Which means saved stack traces can still include file/line info for code that got dlclose'd (or similar). 🎀

⚠️ be careful with this one, fr fr — it can lead to unbounded memory use for programs that repeatedly load and unload shared objects.

Some tools and some functionalities only have limited support for archived debug info. Memcheck fully supports it. 👑 Generally, tools that report errors can use archived debug info to show error stack traces. The known limitations are: Helgrind's past access stack trace of a race condition does not use archived debug info. Massif (and more generally the xtree Massif output format) does not make use of archived debug info. Only Memcheck has been (somewhat) tested with --keep-debuginfo=yes, so other tools may have unknown limitations. 💀

--show-below-main=<yes|no> [default: no] — by default, stack traces for errors do NOT show any functions that appear beneath main, because most of the time it's uninteresting C library stuff and/or gobbledygook. 🙈 Alternatively, if main isn't present in the stack trace, stack traces won't show any functions below main-like functions such as glibc's __libc_start_main. And furthermore, if main-like functions are present in the trace, they get normalised as (below main), just to make the output more deterministic.

If you enable this option, all stack trace entries get shown and main-like functions are not normalised. slay.

--fullpath-after=<string> [default: don't show source paths] — by default Valgrind only shows the filenames in stack traces, not the full paths to source files. When you're using Valgrind in a big project where the sources live in a bunch of different directories, that's lowkey inconvenient. --fullpath-after is the flexible fix. 💖

When this option is present, the path to each source file is shown — with this all-important caveat: if string is found in the path, then the path up to and including string is omitted; otherwise the path is shown unmodified. Note that string is not required to be a prefix of the path.

For example, consider a file named /home/janedoe/blah/src/foo/bar/xyzzy.c. Specifying --fullpath-after=/home/janedoe/blah/src/ will cause Valgrind to show the name as foo/bar/xyzzy.c.

Because the string doesn't have to be a prefix, --fullpath-after=src/ produces the exact same output. This is useful when the path contains arbitrary machine-generated characters. For example, the path /my/build/dir/C32A1B47/blah/src/foo/xyzzy can be pruned to foo/xyzzy using --fullpath-after=/blah/src/. 🔥

If you simply want to see the full path, just specify an empty string: --fullpath-after=. This isn't a special case, merely a logical consequence of the above rules.

Finally, you can use --fullpath-after multiple times. Any appearance of it causes Valgrind to switch to producing full paths and applying the above filtering rule. Each produced path is compared against all the --fullpath-after-specified strings, in the order specified. The first string to match causes the path to be truncated as described above. If none match, the full path is shown. This facilitates chopping off prefixes when the sources are drawn from a number of unrelated directories. ✨

--extra-debuginfo-path=<path> [default: undefined and unused] — by default Valgrind searches in several well-known paths for debug objects, such as /usr/lib/debug/.

However, there may be scenarios where you'd wanna put debug objects at an arbitrary location. Like external storage, when you're running Valgrind on a mobile device with limited local storage. 📱 Another example: a situation where you don't have permission to install debug object packages on the system where you're running Valgrind.

In those scenarios you can provide an absolute path as an extra, final place for Valgrind to search for debug objects by specifying --extra-debuginfo-path=/path/to/debug/objects. The given path will be prepended to the absolute path name of the searched-for object. For example, if Valgrind is looking for the debuginfo for /w/x/y/zz.so and --extra-debuginfo-path=/a/b/c is specified, it will look for a debug object at /a/b/c/w/x/y/zz.so. 🦋

this flag should only be specified once. If you specify it multiple times, only the last instance is honoured. periodt.

--debuginfo-server=ipaddr:port [default: undefined and unused] — okay so this is a new, experimental feature introduced in version 3.9.0. 🧪

In some scenarios it may be convenient to read debuginfo from objects stored on a different machine. With this flag, Valgrind will query a debuginfo server running on ipaddr and listening on port port, if it can't find the debuginfo object in the local filesystem.

The debuginfo server must accept TCP connections on port port. The debuginfo server is contained in the source file auxprogs/valgrind-di-server.c. It will only serve from the directory it is started in. port defaults to 1500 in both client and server if not specified.

If Valgrind looks for the debuginfo for /w/x/y/zz.so by using the debuginfo server, it will strip the pathname components and merely request zz.so on the server. That in turn will look only in its current working directory for a matching debuginfo object.

The debuginfo data is transmitted in small fragments (8 KB) as requested by Valgrind. Each block is compressed using LZO to reduce transmission time. The implementation has been tuned for best performance over a single-stage 802.11g (WiFi) network link. 🌈

Note that checks for matching primary vs debug objects, using GNU debuglink CRC scheme, are performed even when using the debuginfo server. To disable such checking, you need to also specify --allow-mismatched-debuginfo=yes.

By default the Valgrind build system will build valgrind-di-server for the target platform, which is almost certainly not what you want. So far we have been unable to find out how to get automake/autoconf to build it for the build platform. If you want to use it, you will have to recompile it by hand using the command shown at the top of auxprogs/valgrind-di-server.c. 😭

Valgrind can also download debuginfo via debuginfod. See the DEBUGINFOD section for more information. 👑

--allow-mismatched-debuginfo=no|yes [no] — when reading debuginfo from separate debuginfo objects, Valgrind will by default check that the main and debuginfo objects match, using the GNU debuglink mechanism. This guarantees it doesn't read debuginfo from out-of-date debuginfo objects, and also ensures Valgrind can't crash as a result of mismatches. 💅

This check can be overridden using --allow-mismatched-debuginfo=yes. This may be useful when the debuginfo and main objects have not been split in the proper way.

⚠️ be careful though, bestie: this disables all consistency checking, and Valgrind has been observed to crash when the main and debuginfo objects don't match. 💀

--suppressions=<filename> [default: $PREFIX/lib/valgrind/default.supp] — specifies an extra file from which to read descriptions of errors to suppress. You may use up to 100 extra suppression files. 🌸
--gen-suppressions=<yes|no|all> [default: no] — when set to yes, Valgrind will pause after every error shown and print the line:

---- Print suppression ? --- [Return/N/n/Y/y/C/c] ----

Pressing Ret, or N Ret, or n Ret, causes Valgrind to continue execution without printing a suppression for that error. 💖

Pressing Y Ret or y Ret causes Valgrind to write a suppression for that error. You can then cut and paste it into a suppression file if you don't wanna hear about that error ever again. 🙈

When set to all, Valgrind will print a suppression for every reported error, without querying the user. No interruptions, just output. ✨

This option is particularly useful with C++ programs, since it prints out the suppressions with mangled names, as required. 🎀

Note that the suppressions printed are as specific as possible. You may want to common up similar ones by adding wildcards to function names, and by using frame-level wildcards. The wildcarding facilities are powerful yet flexible, and with a bit of careful editing you may be able to suppress a whole family of related errors with only a few suppressions. 🔥

Sometimes two different errors are suppressed by the same suppression, in which case Valgrind will output the suppression more than once — but you only need to have one copy in your suppression file (having more than one won't cause problems though, so no stress). Also, the suppression name is given as <insert a suppression name here>; the name doesn't really matter, it's only used with the -v option, which prints out all used suppression records. 👑

--input-fd=<number> — [default: 0, stdin] 💅 okay so when you're rolling with --gen-suppressions=yes, Valgrind literally stops mid-error and waits for you to type stuff on your keyboard. By default it's reading from standard input (stdin), which is a whole mess for programs that close stdin — like, rude much? This option lets you point it at a different file descriptor to read your input from instead. 🫶
--dsymutil=no|yes — [yes] 🍓 this one only matters if you're running Valgrind on macOS, bestie.

So, macOS has this deferred debug information (debuginfo) linking scheme — very ✨fancy✨, very ✨chaotic✨. When object files that contain debuginfo get linked into a .dylib or an executable, the debuginfo does not get copied into the final file. Nope. Instead you have to link the debuginfo manually by running dsymutil, which is a system-provided utility, on the executable or the .dylib. The combined debuginfo that comes out of that lands in a directory right next to the executable or .dylib, except with the extension .dSYM.

With --dsymutil=no, Valgrind will spot the cases where the .dSYM directory is either missing entirely, or is there but doesn't look like it matches the associated executable or .dylib — most likely because it's out of date, embarrassing. In those situations Valgrind prints a warning message and does literally nothing else. 💀

With --dsymutil=yes, Valgrind will, in those same cases, automatically run dsymutil as necessary to bring the debuginfo up to date. And like, for all practical purposes? If you always use --dsymutil=yes, then you never ever need to run dsymutil manually or as part of your application's build system, because Valgrind will just run it when it needs to. Main character energy from Valgrind honestly. 👑

Valgrind will not attempt to run dsymutil on any executable or library in /usr/, /bin/, /sbin/, /opt/, /sw/, /System/, /Library/ or /Applications/, because dsymutil will always fail in those situations. It fails for two reasons: the debuginfo for those pre-installed system components isn't available anywhere, and also it would need write privileges in those directories. No can do. 🙈

⚠️ Be careful with --dsymutil=yes, bestie, because it will cause pre-existing .dSYM directories to be silently deleted and re-created. Also, dsymutil is quite slow — sometimes, like, excessively so. 😭

--max-stackframe=<number> — [default: 2000000] 🌸 this is the maximum size of a stack frame. If the stack pointer moves by more than this amount, Valgrind assumes your program is switching to a different stack. simple as that.

You might need this option if your program has large stack-allocated arrays. Here's the tea: Valgrind keeps track of your program's stack pointer. If it changes by more than the threshold amount, Valgrind assumes your program is switching to a different stack, and Memcheck behaves differently than it would for a stack pointer change smaller than the threshold. Usually this heuristic works great, ngl. But — if your program allocates large structures on the stack, the heuristic gets fooled, and Memcheck will subsequently report large numbers of invalid stack accesses. This option lets you change the threshold to a different value. 💖

You should only even consider using this option if Valgrind's debug output directs you to do so. And in that case it will literally tell you the new threshold you should specify. It's got you. 🫶

Also, generally speaking, allocating large structures on the stack is a bad idea — because you can easily run out of stack space, especially on systems with limited memory or ones that expect to support large numbers of threads each with a small stack. And also because the error checking Memcheck does is way more effective for heap-allocated data than for stack-allocated data. If you have to use this option, you might wanna consider rewriting your code to allocate on the heap instead of the stack. glow up your code bestie ✨

--main-stacksize=<number> — [default: use current ulimit value] 🌈 specifies the size of the main thread's stack.

To simplify its memory management, Valgrind reserves all the required space for the main thread's stack at startup. Which means it needs to know the required stack size at startup. No guessing games. 💅

By default, Valgrind uses the current ulimit value for the stack size, or 16 MB, whichever is lower. In many cases that gives you a stack size in the range 8 to 16 MB, which almost never overflows for most applications. iconic, honestly.

If you need a larger total stack size, use --main-stacksize to specify it. Only set it as high as you actually need, though, since reserving far more space than you need (like, hundreds of megabytes more than you need) constrains Valgrind's memory allocators and may reduce the total amount of memory Valgrind can use. This is only really of significance on 32-bit machines, fyi.

On Linux, you may request a stack of size up to 2GB. Valgrind will stop with a diagnostic message if the stack cannot be allocated. 🛑

--main-stacksize only affects the stack size for the program's initial thread. It has no bearing on the size of thread stacks, as Valgrind does not allocate those. not it, not its job 💀

You may need to use both --main-stacksize and --max-stackframe together. And it is important to understand that --main-stacksize sets the maximum total stack size, whilst --max-stackframe specifies the largest size of any one stack frame. You will have to work out the --main-stacksize value for yourself (usually, if your application segfaults). But Valgrind will tell you the needed --max-stackframe size, if necessary. Teamwork. 🤝

As discussed further in the description of --max-stackframe, a requirement for a large stack is a sign of potential portability problems. You are best advised to place all large data in heap-allocated memory. periodt. 🎀

--max-threads=<number> — [default: 500] ⭐ by default, Valgrind can handle up to 500 threads. Occasionally that number is too small. Use this option to provide a different limit. E.g. --max-threads=3000.
--max-guard-pages=<number> — [default: 500] 🦋 by default, Valgrind can handle up to 500 madvise guard pages. With thread heavy workloads the default value might not be sufficient. Use this option to provide a different limit. E.g. --max-guard-pages=3000. If --max-guard-pages is not set explicitly, then it will default to the --max-threads setting. cute how they're linked like that 💜
--realloc-zero-bytes-frees=yes|no — [default: yes for glibc, no otherwise] 🧚 okay so the behaviour of realloc() with a size of zero is implementation defined in C17 and undefined in C23. Valgrind tries to work in the same way as the underlying system and C runtime library that it was configured and built on. However, if you use a different C runtime library then this default may be wrong. 😭
- If the value is yes then realloc will deallocate the memory and return NULL.
- If the value is no then realloc will not deallocate the memory and the size will be handled as though it were one byte.

As an example, if you use Valgrind installed via a package on a Linux distro using GNU libc but link your test executable with musl libc or the JEMalloc library then consider using --realloc-zero-bytes-frees=no. iykyk 🔥

Address Sanitizer has a similar and even wordier option: allocator_frees_and_returns_null_on_realloc_zero. not the wordiest competition I wanted to win but here we are 💀

okay so if you're running a tool that brought its own malloc — think Memcheck, Massif, Helgrind, DRD, the whole girlboss crew — these options are the ones that apply. periodt. 💅

--alignment=<number> [default: 8 or 16, depending on the platform] — bestie, by default Valgrind's malloc, realloc, etc, hand back a block whose starting address is 8-byte aligned or 16-byte aligned (which one depends on your platform and matches the platform default, no cap). This option lets you ask for a different alignment instead. but listen — the value you supply has to be greater than or equal to the default, less than or equal to 4096, and it must be a power of two. those are the rules, we don't make them 🔥
--redzone-size=<number> [default: depends on the tool] — so Valgrind's malloc, realloc, etc, add padding blocks before and after every heap block that your program allocates. those little padding blocks are literally called redzones 🎀 and the default redzone size depends on the tool. for example, Memcheck adds and protects a minimum of 16 bytes before and after each block the client allocates — which is how it catches block underruns or overruns of up to 16 bytes.

bumping the redzone size up means you can detect overruns at larger distances, but it also increases the amount of memory Valgrind uses. shrinking the redzone size cuts down Valgrind's memory needs but also reduces your chances of detecting over/underruns — so, ngl, it's not recommended. 🙈

--xtree-memory=none|allocs|full [none] — tools that replace Valgrind's malloc, realloc, etc, can optionally produce an execution tree showing which piece of code is responsible for heap memory usage. want the full lore? see Execution Trees for a detailed explanation about execution trees.
- set it to none and no memory execution tree is produced. simple as that.
- set it to allocs and the memory execution tree gives you the current number of allocated bytes and the current number of allocated blocks.
- set it to full and the memory execution tree gives you 6 different measurements: the current number of allocated bytes and blocks (same values as for allocs), the total number of allocated bytes and blocks, and the total number of freed bytes and blocks. six whole numbers, she's thorough 💜

quick note though — the overhead in cpu and memory to produce an xtree depends on the tool. the cpu overhead is small for the value allocs, since the info needed to produce this report is maintained by the tool in any case. for massif and helgrind, specifying full implies capturing a stack trace for each free operation, while normally these tools only capture an allocation stack trace. for Memcheck, the cpu overhead for the value full is small, because this can only be used in combination with --keep-stacktraces=alloc-and-free or --keep-stacktraces=alloc-then-free, which already record a stack trace for each free operation anyway. and the memory overhead? varies between 5 and 10 words per unique stacktrace in the xtree, plus the memory needed to record the stack trace for the free operations, if that's needed specifically for the xtree. ikyk ✨

--xtree-memory-file=<filename> [default: xtmemory.kcg.%p] — tells Valgrind to produce the xtree memory report in the file you name. any %p or %q sequences in the filename get expanded in exactly the same way as they are for --log-file — go read the description of --log-file for the details, bestie.

oh and also: if your filename contains the extension .ms, the produced file format will be a massif output file format. if it contains the extension .kcg, or no extension is provided or recognised, then the produced file format will be a callgrind output format. 💖

See Execution Trees for a detailed explanation about execution trees formats.

🌀 UNCOMMON OPTIONS 🌀

these ones apply to all tools, since they affect certain obscure workings of the Valgrind core. most people won't need them — it's giving niche, it's giving specialist, and honestly that's iconic of them.

--smc-check=<none|stack|all|all-non-file> [default: all-non-file for x86/amd64/s390x, stack for other archs] — this option controls Valgrind's detection of self-modifying code. and listen, if no checking is done and a program executes some code, then overwrites it with new code, then executes that new code, Valgrind will just keep on executing the translations it made for the old code. that will likely lead to incorrect behaviour and/or crashes. 😭 so, you know, plot twist of the bad kind.

for "modern" architectures — literally anything that's not x86, amd64 or s390x — the default is stack. why? because a correct program must take explicit action to reestablish D-I cache coherence after modifying code. Valgrind observes and honours those actions, so self-modifying code is transparently handled with zero extra cost. slay 💅

for x86, amd64 and s390x though, the program is not required to notify the hardware of required D-I coherence syncing. hence the default is all-non-file, which covers the normal case of generating code into an anonymous (non-file-backed) mmap'd area.

the meanings of the four available settings, bestie, one by one:

no detection — none
detect self-modifying code on the stack (which is used by GCC to implement nested functions) — stack
detect self-modifying code everywhere — all
detect self-modifying code everywhere except in file-backed mappings — all-non-file

running with all will slow Valgrind down noticeably. running with none will rarely speed things up, since very little code gets dynamically generated in most programs. the VALGRIND_DISCARD_TRANSLATIONS client request is an alternative to --smc-check=all and --smc-check=all-non-file that requires more programmer effort but lets Valgrind run your program faster, by telling it precisely when translations need to be re-made. teamwork makes the dream work 🫶

and --smc-check=all-non-file gives you a cheaper but more limited version of --smc-check=all. it adds checks to any translations that do not originate from file-backed memory mappings. typical applications that generate code — say, JITs in web browsers — generate code into anonymous mmaped areas, whereas the "fixed" code of the browser always lives in file-backed mappings. --smc-check=all-non-file takes advantage of this observation, limiting the overhead of checking to code which is likely to be JIT generated. she's smart, she's efficient, she's that girl. ✨

--read-inline-info=<yes|no> [default: see below] — when enabled, Valgrind will read information about inlined function calls from DWARF3 debug info. this slows Valgrind startup and makes it use more memory (typically for each inlined piece of code, 6 words and space for the function name), but it results in more descriptive stacktraces. currently this functionality is enabled by default only for Linux, FreeBSD, Android and Solaris targets, and only for the tools Memcheck, Massif, Helgrind and DRD.

here's an example of some stacktraces with --read-inline-info=no:

==15380== Conditional jump or move depends on uninitialised value(s)
==15380==    at 0x80484EA: main (inlinfo.c:6)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380==    at 0x8048550: fun_noninline (inlinfo.c:6)
==15380==    by 0x804850E: main (inlinfo.c:34)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380==    at 0x8048520: main (inlinfo.c:6)

and here are the same errors with --read-inline-info=yes — look how much more it tells you, obsessed 😍:

==15377== Conditional jump or move depends on uninitialised value(s)
==15377==    at 0x80484EA: fun_d (inlinfo.c:6)
==15377==    by 0x80484EA: fun_c (inlinfo.c:14)
==15377==    by 0x80484EA: fun_b (inlinfo.c:20)
==15377==    by 0x80484EA: fun_a (inlinfo.c:26)
==15377==    by 0x80484EA: main (inlinfo.c:33)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377==    at 0x8048550: fun_d (inlinfo.c:6)
==15377==    by 0x8048550: fun_noninline (inlinfo.c:41)
==15377==    by 0x804850E: main (inlinfo.c:34)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377==    at 0x8048520: fun_d (inlinfo.c:6)
==15377==    by 0x8048520: main (inlinfo.c:35)

--read-var-info=<yes|no> [default: no] — when enabled, Valgrind will read information about variable types and locations from DWARF3 debug info. this slows Valgrind startup significantly and makes it use significantly more memory, but for the tools that can take advantage of it (Memcheck, Helgrind, DRD) it can result in more precise error messages. 💅

for example, here are some standard errors issued by Memcheck:

==15363== Uninitialised byte(s) found during client check request
==15363==    at 0x80484A9: croak (varinfo1.c:28)
==15363==    by 0x8048544: main (varinfo1.c:55)
==15363==  Address 0x80497f7 is 7 bytes inside data symbol "global_i2"
==15363==
==15363== Uninitialised byte(s) found during client check request
==15363==    at 0x80484A9: croak (varinfo1.c:28)
==15363==    by 0x8048550: main (varinfo1.c:56)
==15363==  Address 0xbea0d0cc is on thread 1's stack
==15363==  in frame #1, created by main (varinfo1.c:45)

and here are the same errors with --read-var-info=yes:

==15370== Uninitialised byte(s) found during client check request
==15370==    at 0x80484A9: croak (varinfo1.c:28)
==15370==    by 0x8048544: main (varinfo1.c:55)
==15370==  Location 0x80497f7 is 0 bytes inside global_i2[7],
==15370==  a global variable declared at varinfo1.c:41
==15370==
==15370== Uninitialised byte(s) found during client check request
==15370==    at 0x80484A9: croak (varinfo1.c:28)
==15370==    by 0x8048550: main (varinfo1.c:56)
==15370==  Location 0xbeb4a0cc is 0 bytes inside local var "local"
==15370==  declared at varinfo1.c:46, in frame #1 of thread 1

--vgdb-poll=<number> [default: 5000] — so as part of its main loop, the Valgrind scheduler will poll to check if some activity (like an external command, or some input from a gdb) has to be handled by gdbserver. this activity poll gets done after having run the given number of basic blocks (or slightly more than the given number of basic blocks, close enough 🎀). this poll is pretty cheap, which is why the default value is set relatively low. you might want to decrease this value even further if vgdb can't use the ptrace system call to interrupt Valgrind when all threads are (most of the time) blocked in a system call. 💜
--vgdb-shadow-registers=no|yes [default: no] — turn this on and gdbserver will ✨expose the Valgrind shadow registers to GDB✨. Which means yes, bestie, you can actually look at their values and change them from inside GDB. Heads up though: exposing shadow registers only works with GDB version 7.1 or later. no ancient GDB energy 💅
--vgdb-prefix=<prefix> [default: /tmp/vgdb-pipe] — so to talk to gdb/vgdb, the Valgrind gdbserver creates 3 files: two named FIFOs and a mmap shared memory file. This option is the one that decides the directory and the prefix used when those files get created. the naming rights, basically 🎀
--run-libc-freeres=<yes|no> [default: yes] — okay so this one only matters when you're running Valgrind on Linux with GNU libc. fr fr.

The GNU C library (libc.so), which literally every program uses, may allocate memory for its own little purposes. And usually it does not bother freeing that memory when the program ends — because why would it, the Linux kernel reclaims all process resources when a process exits anyway, so freeing would just slow things down. lazy but valid

The glibc authors clocked that this behaviour makes leak checkers (hi, Valgrind 💖) falsely report leaks in glibc when a leak check happens at exit. So to dodge that, they provided a routine called __libc_freeres specifically to make glibc release all the memory it has allocated. Memcheck therefore tries to run __libc_freeres at exit. slay.

Unfortunately 😭, in some very old versions of glibc, __libc_freeres is buggy enough to cause segmentation faults. This was particularly noticeable on Red Hat 7.1. So this option exists to inhibit the run of __libc_freeres. If your program seems to run fine on Valgrind but segfaults at exit, --run-libc-freeres=no may fix that — although at the cost of possibly falsely reporting space leaks in libc.so.

trade-off alert: fixing the exit segfault means you might get fake leak reports from libc.so. pick your poison bestie 💀

--run-cxx-freeres=<yes|no> [default: yes] — this one is only relevant when running Valgrind on Linux, FreeBSD or Solaris C++ programs using libstdc++.

The GNU Standard C++ library (libstdc++.so), which is used by all C++ programs compiled with g++, may allocate memory for its own uses. And usually it doesn't bother to free that memory when the program ends — no point, since the kernel reclaims all process resources when a process exits anyway, so it would just slow things down.

The gcc authors realised this behaviour causes leak checkers like Valgrind to falsely report leaks in libstdc++ when a leak check is done at exit. To avoid that, they provided a routine called __gnu_cxx::__freeres specifically to make libstdc++ release all memory it has allocated. Memcheck therefore tries to run __gnu_cxx::__freeres at exit.

And for the sake of flexibility and unforeseen problems with __gnu_cxx::__freeres, the option --run-cxx-freeres=no exists — although, again, at the cost of possibly falsely reporting space leaks in libstdc++.so.

--sim-hints=hint1,hint2,... — passes miscellaneous hints to Valgrind that slightly modify the simulated behaviour in nonstandard or dangerous ways, possibly to help simulate strange features. By default no hints are enabled.

Use with caution! ⚠️ these are literally described as nonstandard and dangerous.

Currently known hints are:

lax-ioctls: be very lax about ioctl handling — the only assumption is that the size is correct. Doesn't require the full buffer to be initialised when writing. Without this, using some device drivers with a large number of strange ioctl commands becomes very tiresome. (we love a low-effort mode)
fuse-compatible: enables special handling for certain system calls that may block in a FUSE file-system. This may be necessary when running Valgrind on a multi-threaded program that uses one thread to manage a FUSE file-system and another thread to access that file-system.
enable-outer: enables some special magic needed when the program being run is itself Valgrind. 🪆 valgrind-ception
no-inner-prefix: disables printing the prefix > in front of each stdout or stderr output line in an inner Valgrind being run by an outer Valgrind. This is useful when running Valgrind regression tests in an outer/inner setup. Note that the prefix > will always be printed in front of the inner debug logging lines.
no-nptl-pthread-stackcache: this hint is only relevant when running Valgrind on Linux — it is ignored on FreeBSD, Solaris and macOS.

The GNU glibc pthread library (libpthread.so), which is used by pthread programs, maintains a cache of pthread stacks. When a pthread terminates, the memory used for the pthread stack and some thread local storage related data structure are not always directly released. This memory is kept in a cache (up to a certain size), and is re-used if a new thread is started.

This cache causes the helgrind tool to report some false positive race condition errors on this cached memory, because helgrind does not understand the internal glibc cache synchronisation primitives. So when using helgrind, disabling the cache helps avoid false positive race conditions — in particular when using thread local storage variables (e.g. variables using the __thread qualifier).

When using the memcheck tool, disabling the cache ensures the memory used by glibc to handle __thread variables is directly released when a thread terminates.

Note: Valgrind disables the cache using some internal knowledge of the glibc stack cache implementation and by examining the debug information of the pthread library. This technique is thus somewhat fragile and might not work for all glibc versions. This has been successfully tested with various glibc versions (e.g. 2.11, 2.16, 2.18) on various platforms. fragile but tested, iykyk

lax-doors: (Solaris only) be very lax about door syscall handling over unrecognised door file descriptors. Does not require that the full buffer is initialised when writing. Without this, programs using libdoor(3LIB) functionality with completely proprietary semantics may report a large number of false positives.
fallback-llsc: (MIPS and ARM64 only) enables an alternative implementation of Load-Linked (LL) and Store-Conditional (SC) instructions. The standard implementation gives more correct behaviour, but can cause indefinite looping on certain processor implementations that are intolerant of extra memory references between LL and SC. So far this is known only to happen on Cavium 3 cores. You should not need to use this flag, since the relevant cores are detected at startup and the alternative implementation is automatically enabled if necessary. There is no equivalent anti-flag: you cannot force-disable the alternative implementation if it is automatically enabled. The underlying problem exists because the "standard" implementation of LL and SC is done by copying through LL and SC instructions into the instrumented code. However, tools may insert extra instrumentation memory references in between the LL and SC instructions. These memory references are not present in the original uninstrumented code, and their presence in the instrumented code can cause the SC instructions to persistently fail, leading to indefinite looping in LL-SC blocks. The alternative implementation gives correct behaviour of LL and SC instructions between threads in a process, up to and including the ABA scenario. It also gives correct behaviour between a Valgrinded thread and a non-Valgrinded thread running in a different process, that communicate via shared memory, but only up to and including correct CAS behaviour — in this case the ABA scenario may not be correctly handled. so much lore for one flag bestie 😭

--scheduling-quantum=<number> [default: 100000] — this option controls the maximum number of basic blocks executed by a thread before releasing the lock that Valgrind uses to serialise thread execution. Smaller values give finer interleaving but increase the scheduling overhead. Finer interleaving can be useful to reproduce race conditions with helgrind or DRD. For more details about the Valgrind thread serialisation scheme and its impact on performance and thread scheduling, see Scheduling and Multi-Thread Performance.
--fair-sched=<no|yes|try> [default: no] — controls the locking mechanism Valgrind uses to serialise thread execution. That locking mechanism controls how threads get scheduled, and different settings give different trade-offs between fairness and performance. For more details about the Valgrind thread serialisation scheme and its impact on performance and thread scheduling, see Scheduling and Multi-Thread Performance.
- The value --fair-sched=yes activates a fair scheduler. In short: if multiple threads are ready to run, the threads will be scheduled in a round robin fashion. This mechanism is not available on all platforms or Linux versions. If it's not available, using --fair-sched=yes will cause Valgrind to terminate with an error. so dramatic 💀 You may find this setting improves overall responsiveness if you're running an interactive multithreaded program on Valgrind — for example, a web browser. 🌈
- The value --fair-sched=try activates fair scheduling if it's available on the platform. Otherwise, it will automatically fall back to --fair-sched=no.
- The value --fair-sched=no activates a scheduler which does not guarantee fairness between threads ready to run, but which in general gives the highest performance. speed over justice, honestly valid
--kernel-variant=variant1,variant2,... — handles system calls and ioctls arising from minor variants of the default kernel for this platform. Useful for running on hacked kernels, or with kernel modules which support nonstandard ioctls, for example.

Use with caution. If you don't understand what this option does then you almost certainly don't need it. 🙈

Currently known variants are:

bproc: support the sys_broc system call on x86. This is for running on BProc, which is a minor variant of standard Linux which is sometimes used for building clusters.

android-no-hw-tls — okay so some versions of the Android emulator for ARM just… don't give you a hardware TLS (thread-local state) register?</p> And then Valgrind crashes at startup. Rude. Use this variant to select software support for TLS instead 💅
- android-gpu-sgx5xx — use this to support handling of proprietary ioctls for the PowerVR SGX 5XX series of GPUs on Android devices. Ngl, failing to select this doesn't cause any stability problems, but it may cause Memcheck to report false errors after your program performs GPU-specific ioctls, and false errors are not the vibe 🫠
- android-gpu-adreno3xx — similarly (same energy, different GPU), use this to support handling of proprietary ioctls for the Qualcomm Adreno 3XX series of GPUs on Android devices.

`--merge-recursive-frames=<number>` [default: `0`]

Bestie, some recursive algorithms are out here farming stack traces. Like, balanced binary tree implementations? They create so many different stack traces, each one containing cycles of calls. And a cycle is defined as two identical program counter values separated by zero or more other program counter values. So Valgrind may then use a lot of memory storing all these stack traces 😭 Which is honestly a poor use of memory, considering that such stack traces contain repeated uninteresting recursive calls instead of more interesting information, like the function that has initiated the recursive call. Not iconic. Not the moment.

So the option --merge-recursive-frames=<number> instructs Valgrind to detect and merge recursive call cycles having a size of up to <number> frames. When such a cycle is detected, Valgrind records the cycle in the stack trace as a unique program counter. Slay.

The value 0 (the default) causes no recursive call merging. A value of 1 will cause stack traces of simple recursive algorithms (for example, a factorial implementation) to be collapsed. A value of 2 will usually be needed to collapse stack traces produced by recursive algorithms such as binary trees, quick sort, etc. Higher values might be needed for more complex recursive algorithms.

⚠️ Note: recursive calls are detected by analysis of program counter values. They are not detected by looking at function names. Keep that in mind, iykyk 💖

`--num-transtab-sectors=<number>` [default: `6` for Android platforms, `16` for all others]

Okay so Valgrind translates and instruments your program's machine code in small fragments (basic blocks). Those translations live in a translation cache that's divided into a number of sections (sectors). If the cache is full, the sector containing the oldest translations gets emptied and reused. And if those old translations are needed again?? Valgrind has to re-translate and re-instrument the corresponding machine code, which is expensive 💀

If the "executed instructions" working set of a program is big, increasing the number of sectors may improve performance by reducing the number of re-translations needed. Sectors are allocated on demand. Once allocated, a sector can never be freed, and it occupies considerable space, depending on the tool and the value of --avg-transtab-entry-size (about 40 MB per sector for Memcheck — she's thicc). Use the option --stats=yes to obtain precise information about the memory used by a sector and the allocation and recycling of sectors ✨

`--avg-transtab-entry-size=<number>` [default: `0`, meaning use tool provided default]

Average size of translated basic block 🎀 This average size is used to dimension the size of a sector. Each tool provides a default value to be used. If this default value is too small, the translation sectors will become full too quickly. If this default value is too big, a significant part of the translation sector memory will just be… sitting there unused 🙈

Note that the average size of a basic block translation depends on the tool, and might depend on tool options. For example, the memcheck option --track-origins=yes increases the size of the basic block translations. Use --avg-transtab-entry-size to tune the size of the sectors, either to gain memory or to avoid too many retranslations.

`--aspace-minaddr=<address>` [default: depends on the platform]

To avoid potential conflicts with some system libraries, Valgrind does not use the address space below the --aspace-minaddr value, keeping it reserved in case a library specifically requests memory in this region 🫶 So, some "pessimistic" value is guessed by Valgrind depending on the platform. On linux, by default, Valgrind avoids using the first 64MB even if typically there is no conflict in this complete zone.

You can use the option --aspace-minaddr to have your memory hungry application benefitting from more of this lower memory 👑 On the other hand, if you encounter a conflict, increasing the aspace-minaddr value might solve it. Conflicts will typically manifest themselves with mmap failures in the low range of the address space. The provided address must be page aligned and must be equal or bigger to 0x1000 (4KB). To find the default value on your platform, do something such as:

valgrind -d -d date 2>&1 | grep -i minaddr

🚨 Values lower than 0x10000 (64KB) are known to create problems on some distributions. So like… don't.

`--valgrind-stacksize=<number>` [default: `1MB`]

For each thread, Valgrind needs its own 'private' stack. The default size for these stacks is largely dimensioned, and so should be sufficient in most cases. In case the size is too small, Valgrind will segfault 😭 Before segfaulting, a warning might be produced by Valgrind when approaching the limit.

Use the option --valgrind-stacksize if such an (unlikely) warning is produced, or if Valgrind dies due to a segmentation violation. Such segmentation violations have been seen when demangling huge C++ symbols, fr fr.

If your application uses many threads and needs a lot of memory, you can gain some memory by reducing the size of these Valgrind stacks using the option --valgrind-stacksize 💖

`--show-emwarns=<yes|no>` [default: `no`]

When enabled, Valgrind will emit warnings about its CPU emulation in certain cases. These are usually not interesting 🙈 so like, no pressure bestie.

`--require-text-symbol=:sonamepatt:fnnamepatt`

Okay this one is a vibe check with actual teeth 💅 When a shared object whose soname matches sonamepatt is loaded into the process, Valgrind examines all the text symbols it exports. If none of those match fnnamepatt, it prints an error message and abandons the run. This makes it possible to ensure that the run does not continue unless a given shared object contains a particular function name ⭐

Both sonamepatt and fnnamepatt can be written using the usual ? and * wildcards. For example: ":*libc.so*:foo?bar". You may use characters other than a colon to separate the two patterns. It is only important that the first character and the separator character are the same. For example, the above example could also be written "Q*libc.so*Qfoo?bar". Multiple --require-text-symbol flags are allowed, in which case shared objects that are loaded into the process will be checked against all of them.

The purpose of this is to support reliable usage of marked-up libraries 🧚 For example, suppose we have a version of GCC's libgomp.so which has been marked up with annotations to support Helgrind. It is only too easy and confusing to load the wrong, un-annotated libgomp.so into the application. So the idea is: add a text symbol in the marked-up library, for example annotated_for_helgrind_3_6, and then give the flag

--require-text-symbol=:*libgomp*so*:annotated_for_helgrind_3_6

so that when libgomp.so is loaded, Valgrind scans its symbol table, and if the symbol isn't present the run is aborted, rather than continuing silently with the un-marked-up library. Periodt.

💡 Note that you should put the entire flag in quotes to stop shells expanding up the * and ? wildcards!

`--soname-synonyms=syn1=pattern1,syn2=pattern2,...`

When a shared library is loaded, Valgrind checks for functions in the library that must be replaced or wrapped ✨ For example, Memcheck replaces some string and memory functions (strchr, strlen, strcpy, memchr, memcpy, memmove, etc.) with its own versions. Such replacements are normally done only in shared libraries whose soname matches a predefined soname pattern (e.g. libc.so* on linux). By default, no replacement is done for a statically linked binary or for alternative libraries, except for the allocation functions (malloc, free, calloc, memalign, realloc, operator new, operator delete, etc.).

Such allocation functions are intercepted by default in any shared library or in the executable if they are exported as global symbols. This means that if a replacement allocation library such as tcmalloc is found, its functions are also intercepted by default 👀 In some cases, the replacements allow --soname-synonyms to specify one additional synonym pattern, giving flexibility in the replacement. Or to prevent interception of all public allocation symbols.

Currently, this flexibility is only allowed for the malloc related functions, using the synonym somalloc. This synonym is usable for all tools doing standard replacement of malloc related functions (e.g. memcheck, helgrind, drd, massif, dhat).

Alternate malloc library — to replace the malloc related functions in a specific alternate library with soname mymalloclib.so (and not in any others), give the option --soname-synonyms=somalloc=mymalloclib.so. A pattern can be used to match multiple libraries sonames. For example, --soname-synonyms=somalloc=*tcmalloc* will match the soname of all variants of the tcmalloc library (native, debug, profiled, ... tcmalloc variants) 🍓

📖 Note: the soname of a elf shared library can be retrieved using the readelf utility.

Replacements in a statically linked library are done by using the NONE pattern. For example, if you link with libtcmalloc.a, and only want to intercept the malloc related functions in the executable (and standard libraries) themselves, but not any other shared libraries, you can give the option --soname-synonyms=somalloc=NONE. Note that a NONE pattern will match the main executable and any shared library having no soname 🌈
To only intercept allocation symbols in the default system libraries, but not in any other shared library or the executable that defines public malloc or operator new related functions — use a non-existing library name, like this: --soname-synonyms=somalloc=nouserintercepts (where nouserintercepts can be literally any non-existing library name, it's just a placeholder vibe 💅).
- The shared library of the dynamic (runtime) linker is excluded from the search for global public symbols, like the ones for the malloc related functions (identified by the somalloc synonym). ok so it's just not invited to that party 🚫

`--progress-interval=<number>` [default: `0`, meaning 'disabled']

So this one is an enhancement to Valgrind's own debugging output. Ngl, it's unlikely to be of interest to end users — it's giving internal-tea-only ☕ but here's the whole thing anyway bestie.

When number is set to a non-zero value, Valgrind will print a one-line progress summary every number seconds. Valid settings for number are between 0 and 3600 inclusive. Here's some example output with number set to 10:

PROGRESS: U 110s, W 113s, 97.3% CPU, EvC 414.79M, TIn 616.7k, TOut 0.5k, #thr 67
PROGRESS: U 120s, W 124s, 96.8% CPU, EvC 505.27M, TIn 636.6k, TOut 3.0k, #thr 64
PROGRESS: U 130s, W 134s, 97.0% CPU, EvC 574.90M, TIn 657.5k, TOut 3.0k, #thr 63

Each line shows:

U: total user time
W: total wallclock time
CPU: overall average cpu use
EvC: number of event checks. An event check is a backwards branch in the simulated program, so this is a measure of forward progress of the program
TIn: number of code blocks instrumented by the JIT
TOut: number of instrumented code blocks that have been thrown away
#thr: number of threads in the program

From the progress of these, it is possible to observe:

when the program is compute bound (TIn rises slowly, EvC rises rapidly)
when the program is in a spinloop (TIn/TOut fixed, EvC rises rapidly)
when the program is JIT-bound (TIn rises rapidly)
when the program is rapidly discarding code (TOut rises rapidly)
when the program is about to achieve some expected state (EvC arrives at some value you expect)
when the program is idling (U rises more slowly than W)

🐛 DEBUGGING VALGRIND OPTIONS 🐛

There are also some options for debugging Valgrind itself. You shouldn't need to use them in the normal run of things, fr fr. If you wish to see the list, use the --help-debug option. iykyk 🔍

👑 MEMCHECK OPTIONS 👑

`--leak-check=<no|summary|yes|full>` [default: `summary`]

When enabled, search for memory leaks when the client program finishes. If set to summary, it says how many leaks occurred. If set to full or yes, each individual leak will be shown in detail and/or counted as an error, as specified by the options --show-leak-kinds and --errors-for-leak-kinds. The way that this one single option changes your entire debugging session… iconic 💅

If --xml=yes is given, memcheck will automatically use the value --leak-check=full. You can use --show-leak-kinds=none to reduce the size of the xml output if you are not interested in the leak results. no pressure, just saying 💖

`--leak-resolution=<low|med|high>` [default: `high`]

When doing leak checking, this determines how willing Memcheck is to consider different backtraces to be the same for the purposes of merging multiple leaks into a single leak report. So:

low — only the first two entries need to match.
med — four entries have to match.
high — all entries need to match.

For hardcore leak debugging, you probably want to use --leak-resolution=high together with --num-callers=40 or some such large number. bestie going feral mode 🔥

Note that the --leak-resolution setting does not affect Memcheck's ability to find leaks. It only changes how the results are presented. so like, it's a glow-up for the report, not new info ✨

`--show-leak-kinds=<set>` [default: `definite,possible`]

Specifies the leak kinds to show in a full leak search, in one of the following ways:

a comma separated list of one or more of definite indirect possible reachable.
all to specify the complete set (all leak kinds). It is equivalent to --show-leak-kinds=definite,indirect,possible,reachable.
none for the empty set.

`--errors-for-leak-kinds=<set>` [default: `definite,possible`]

Specifies the leak kinds to count as errors in a full leak search. The <set> is specified similarly to --show-leak-kinds. yeah it's the same menu, just deciding which ones get marked as a crime 🙈

`--leak-check-heuristics=<set>` [default: `all`]

Specifies the set of leak check heuristics to be used during leak searches. The heuristics control which interior pointers to a block cause it to be considered as reachable. The heuristic set is specified in one of the following ways:

a comma separated list of one or more of stdstring length64 newarray multipleinheritance.
all to activate the complete set of heuristics. It is equivalent to --leak-check-heuristics=stdstring,length64,newarray,multipleinheritance.
none for the empty set.

Note that these heuristics are dependent on the layout of the objects produced by the C++ compiler. They have been tested with some gcc versions (e.g. 4.4 and 4.7). They might not work properly with other C++ compilers. so like… your mileage may vary depending on which compiler is your main character 😭

`--show-reachable=<yes|no>` , `--show-possibly-lost=<yes|no>`

These options provide an alternative way to specify the leak kinds to show:

--show-reachable=no --show-possibly-lost=yes is equivalent to --show-leak-kinds=definite,possible.
--show-reachable=no --show-possibly-lost=no is equivalent to --show-leak-kinds=definite.
--show-reachable=yes is equivalent to --show-leak-kinds=all.

Note that --show-possibly-lost=no has no effect if --show-reachable=yes is specified. it literally gets overruled, periodt 👑

`--xtree-leak=<no|yes>` [`no`]

If set to yes, the results for the leak search done at exit will be output in a 'Callgrind Format' execution tree file. Note that this automatically sets the options --leak-check=full and --show-leak-kinds=all, to allow xtree visualisation tools such as kcachegrind to select what kind to leak to visualize. The produced file will contain the following events:

RB : Reachable Bytes
PB : Possibly lost Bytes
IB : Indirectly lost Bytes
DB : Definitely lost Bytes (direct plus indirect)
DIB : Definitely Indirectly lost Bytes (subset of DB)
RBk : reachable Blocks
PBk : Possibly lost Blocks
IBk : Indirectly lost Blocks
DBk : Definitely lost Blocks

The increase or decrease for all events above will also be output in the file to provide the delta (increase or decrease) between 2 successive leak searches. For example, iRB is the increase of the RB event, dPBk is the decrease of PBk event. The values for the increase and decrease events will be zero for the first leak search done. 🦋

See Execution Trees for a detailed explanation about execution trees.

`--xtree-leak-file=<filename>` [default: `xtleak.kcg.%p`]

Specifies that Valgrind should produce the xtree leak report in the specified file. Any %p, %q or %n sequences appearing in the filename are expanded in exactly the same way as they are for --log-file. See the description of --log-file for details. 💅

See Execution Trees for a detailed explanation about execution trees formats.

`--undef-value-errors=<yes|no>` [default: `yes`]

Controls whether Memcheck reports uses of undefined value errors. Set this to no if you don't want to see undefined value errors. It also has the side effect of speeding up Memcheck somewhat. AddrCheck (removed in Valgrind 3.1.0) functioned like Memcheck with --undef-value-errors=no. so yeah, this is the "ignore the problem and things go faster" setting, it's giving denial-as-a-performance-strategy 😭✨

`--track-origins=<yes|no>` [default: `no`]

Controls whether Memcheck tracks the origin of uninitialised values. By default, it does not, which means that although it can tell you that an uninitialised value is being used in a dangerous way, it cannot tell you where the uninitialised value came from. This often makes it difficult to track down the root problem. literally the "somebody is yelling but nobody knows who" situation 💀

When set to yes, Memcheck keeps track of the origins of all uninitialised values. Then, when an uninitialised value error is reported, Memcheck will try to show the origin of the value. An origin can be one of the following four places: a heap block, a stack allocation, a client request, or miscellaneous other sources (eg, a call to brk).

For uninitialised values originating from a heap block, Memcheck shows where the block was allocated. For uninitialised values originating from a stack allocation, Memcheck can tell you which function allocated the value, but no more than that — typically it shows you the source location of the opening brace of the function. So you should carefully check that all of the function's local variables are initialised properly. 👀 check your locals bestie, all of them.

Performance overhead: origin tracking is expensive. It halves Memcheck's speed and increases memory use by a minimum of 100MB, and possibly more. Nevertheless it can drastically reduce the effort required to identify the root cause of uninitialised value errors, and so is often a programmer productivity win, despite running more slowly. so like — slower, hungrier, but so much smarter 🧠💖

Accuracy: Memcheck tracks origins quite accurately. To avoid very large space and time overheads, some approximations are made. It is possible, although unlikely, that Memcheck will report an incorrect origin, or not be able to identify any origin. 🎀

Note that the combination --track-origins=yes and --undef-value-errors=no is nonsensical. Memcheck checks for and rejects this combination at startup. it literally refuses, no cap 🚫

`--partial-loads-ok=<yes|no>` [default: `yes`]

Controls how Memcheck handles 32-, 64-, 128- and 256-bit naturally aligned loads from addresses for which some bytes are addressable and others are not. When yes, such loads do not produce an address error. Instead, loaded bytes originating from illegal addresses are marked as uninitialised, and those corresponding to legal addresses are handled in the normal way.

When no, loads from partially invalid addresses are treated the same as loads from completely invalid addresses: an illegal-address error is issued, and the resulting bytes are marked as initialised. so it's the strict mode vs the chill mode 🌸

Note that code that behaves in this way is in violation of the ISO C/C++ standards, and should be considered broken. If at all possible, such code should be fixed. for real for real, this is not the vibe you want in your codebase ✋💀

--expensive-definedness-checks=<no|auto|yes> — [default: auto]

okay so this one is about how much ✨effort✨ Memcheck puts into checking whether certain values are defined or not. It controls whether Memcheck should employ more precise but also more expensive (time consuming) instrumentation when checking the definedness of certain values. In particular — and this is the tea — it affects the instrumentation of integer adds, subtracts and equality comparisons. 🧮

Pick --expensive-definedness-checks=yes and Memcheck uses the most accurate analysis possible. This minimises false error rates but can cause up to 30% performance degradation. So like, accurate but she's slow. 😭

Pick --expensive-definedness-checks=no and Memcheck uses the cheapest instrumentation possible. This maximises performance but will normally give you an unusably high false error rate. Bestie, do not.

The default, --expensive-definedness-checks=auto, is strongly recommended — like, please just leave it alone, she knows what she's doing 💅. This causes Memcheck to use the minimum of expensive instrumentation needed to achieve the same false error rate as --expensive-definedness-checks=yes. It also enables an instrumentation-time analysis pass which aims to further reduce the costs of accurate instrumentation. Overall, the performance loss is generally around 5% relative to --expensive-definedness-checks=no, although this is strongly workload dependent. Note that the exact instrumentation settings in this mode are architecture dependent.

--keep-stacktraces=alloc|free|alloc-and-free|alloc-then-free|none — [default: alloc-and-free]

This controls which stack trace(s) to keep for malloc'd and/or free'd blocks. 🧵

With alloc-then-free, a stack trace is recorded at allocation time, and is associated with the block. When the block is freed, a second stack trace is recorded, and this replaces the allocation stack trace. As a result, any "use after free" errors relating to this block can only show a stack trace for where the block was freed.

With alloc-and-free, both allocation and the deallocation stack traces for the block are stored. Hence a "use after free" error will show both, which may make the error easier to diagnose. Compared to alloc-then-free, this setting slightly increases Valgrind's memory use as the block contains two references instead of one. Double the receipts, double the memory 📝📝.

With alloc, only the allocation stack trace is recorded (and reported). With free, only the deallocation stack trace is recorded (and reported). These values somewhat decrease Valgrind's memory and cpu usage. They can be useful depending on the error types you are searching for and the level of detail you need to analyse them. For example, if you are only interested in memory leak errors, it is sufficient to record the allocation stack traces. 🫶

With none, no stack traces are recorded for malloc and free operations. If your program allocates a lot of blocks and/or allocates/frees from many different stack traces, this can significantly decrease cpu and/or memory required. Of course, few details will be reported for errors related to heap blocks. It's giving minimalism but at a cost bestie.

Note that once a stack trace is recorded, Valgrind keeps the stack trace in memory even if it is not referenced by any block. Some programs (for example, recursive algorithms) can generate a huge number of stack traces. If Valgrind uses too much memory in such circumstances, you can reduce the memory required with the options --keep-stacktraces and/or by using a smaller value for the option --num-callers. 🚨

Also! If you want to use --xtree-memory=full memory profiling (see Execution Trees), then you cannot specify --keep-stacktraces=free or --keep-stacktraces=none. No mixing, sorry, them's the rules 🙈.

--freelist-vol=<number> — [default: 20000000]

So when the client program releases memory using free (in C) or delete (C++), that memory is not immediately made available for re-allocation. Instead, it is marked inaccessible and placed in a queue of freed blocks. The purpose is to defer as long as possible the point at which freed-up memory comes back into circulation. This increases the chance that Memcheck will be able to detect invalid accesses to blocks for some significant period of time after they have been freed. Basically she's keeping the evidence around a lil longer 🔍.

This option specifies the maximum total size, in bytes, of the blocks in the queue. The default value is twenty million bytes. Increasing this increases the total amount of memory used by Memcheck but may detect invalid uses of freed blocks which would otherwise go undetected.

--freelist-big-blocks=<number> — [default: 1000000]

When making blocks from the queue of freed blocks available for re-allocation, Memcheck will in priority re-circulate the blocks with a size greater or equal to --freelist-big-blocks. This ensures that freeing big blocks (in particular freeing blocks bigger than --freelist-vol) does not immediately lead to a re-circulation of all (or a lot of) the small blocks in the free list. In other words, this option increases the likelihood to discover dangling pointers for the "small" blocks, even when big blocks are freed. Big blocks go first, small blocks stay put 🐘➡️🐜.

Setting a value of 0 means that all the blocks are re-circulated in a FIFO order.

--workaround-gcc296-bugs=<yes|no> — [default: no]

When enabled, assume that reads and writes some small distance below the stack pointer are due to bugs in GCC 2.96, and does not report them. The "small distance" is 256 bytes by default. Note that GCC 2.96 is the default compiler on some ancient Linux distributions (RedHat 7.X) and so you may need to use this option. Do not use it if you do not have to, as it can cause real errors to be overlooked. A better alternative is to use a more recent GCC in which this bug is fixed. ✨🦋

You may also need to use this option when working with GCC 3.X or 4.X on 32-bit PowerPC Linux. This is because GCC generates code which occasionally accesses below the stack pointer, particularly for floating-point to/from integer conversions. This is in violation of the 32-bit PowerPC ELF specification, which makes no provision for locations below the stack pointer to be accessible.

This option is deprecated as of version 3.12 and may be removed from future versions. You should instead use --ignore-range-below-sp to specify the exact range of offsets below the stack pointer that should be ignored. A suitable equivalent is --ignore-range-below-sp=1024-1. 👑

--ignore-range-below-sp=<number>-<number>

This is a more general replacement for the deprecated --workaround-gcc296-bugs option (glow up 💅). When specified, it causes Memcheck not to report errors for accesses at the specified offsets below the stack pointer. The two offsets must be positive decimal numbers and — somewhat counterintuitively — the first one must be larger, in order to imply a non-wraparound address range to ignore. So yeah, the order is upside down, that's just how she is 🙃. For example, to ignore 4 byte accesses at 8192 bytes below the stack pointer, use --ignore-range-below-sp=8192-8189. Only one range may be specified.

--show-mismatched-frees=<yes|no> — [default: yes]

When enabled, Memcheck checks that heap blocks are deallocated using a function that matches the allocating function. That is, it expects free to be used to deallocate blocks allocated by malloc, delete for blocks allocated by new, and delete[] for blocks allocated by new[]. If a mismatch is detected, an error is reported. This is in general important because in some environments, freeing with a non-matching function can cause crashes. 💀

There is however a scenario where such mismatches cannot be avoided. That is when the user provides implementations of new/new[] that call malloc and of delete/delete[] that call free, and these functions are asymmetrically inlined. For example, imagine that delete[] is inlined but new[] is not. The result is that Memcheck "sees" all delete[] calls as direct calls to free, even when the program source contains no mismatched calls.

This causes a lot of confusing and irrelevant error reports. --show-mismatched-frees=no disables these checks. It is not generally advisable to disable them, though, because you may miss real errors as a result. 😭

--show-realloc-size-zero=<yes|no> — [default: yes]

When enabled, Memcheck checks for uses of realloc with a size of zero. This usage of realloc is unsafe since it is not portable. On some systems it will behave like free. On other systems it will either do nothing or else behave like a call to free followed by a call to malloc with a size of zero. It's giving "everybody does it differently" energy and honestly bestie, that's a red flag 🚩.

--ignore-ranges=0xPP-0xQQ[,0xRR-0xSS]

Any ranges listed in this option (and multiple ranges can be specified, separated by commas) will be ignored by Memcheck's addressability checking. Just vibes only in those ranges ✨🌈. Make sure you use the correct hex format, bestie.

--malloc-fill=<hexnumber>

Fills blocks allocated by malloc, new, etc, but not by calloc, with the specified byte. This can be useful when trying to shake out obscure memory corruption problems. The allocated area is still regarded by Memcheck as undefined — this option only affects its contents. Note that --malloc-fill does not affect a block of memory when it is used as argument to client requests VALGRIND_MEMPOOL_ALLOC or VALGRIND_MALLOCLIKE_BLOCK. 🎀

--free-fill=<hexnumber>

Fills blocks freed by free, delete, etc, with the specified byte value. This can be useful when trying to shake out obscure memory corruption problems. The freed area is still regarded by Memcheck as not valid for access — this option only affects its contents. Note that --free-fill does not affect a block of memory when it is used as argument to client requests VALGRIND_MEMPOOL_FREE or VALGRIND_FREELIKE_BLOCK. 🦋

🎀 CACHEGRIND OPTIONS 🎀

--cachegrind-out-file=<file> — bestie, instead of dumping your Cachegrind output into the default file (cachegrind.out.<pid>), send it wherever you want with this. And yes, the %p and %q format specifiers work here too, so you can shove the process ID and/or the contents of an environment variable right into the name — literally the same deal as the core option --log-file. 💅
--cache-sim=no|yes [no] — turns the collection of cache access counts and cache miss counts on or off.
--branch-sim=no|yes [no] — turns collecting branch instruction counts and misprediction counts on or off.
--instr-at-start=no|yes [yes] — switches instrumentation at the very start of execution on or off. Team it up with CACHEGRIND_START_INSTRUMENTATION and CACHEGRIND_STOP_INSTRUMENTATION if you only wanna measure part of a client program's execution — like, a vibe-checked little slice of the run. ✨
--I1=<size>,<associativity>,<line size> — you're setting the size, associativity and line size of the level 1 instruction cache. Only useful with --cache-sim=yes tho.
--D1=<size>,<associativity>,<line size> — same energy but for the level 1 data cache: size, associativity, line size. Only useful with --cache-sim=yes.
--LL=<size>,<associativity>,<line size> — and this one? The last-level cache. You give it size, associativity and line size. Only useful with --cache-sim=yes. 🧚

💫 CALLGRIND OPTIONS 💫

--callgrind-out-file=<file> — write the profile data to file instead of the default output file, which is callgrind.out.<pid>. The %p and %q format specifiers can embed the process ID and/or the contents of an environment variable in the name, exactly like the core option --log-file does. And heads up: when multiple dumps get made, the file name gets modified even further — more on that below. 🙈
--dump-line=<no|yes> [default: yes] — this says event counting should happen at source line granularity, which means you get source annotation for sources compiled with debug info (-g). 👑
--dump-instr=<no|yes> [default: no] — this says event counting should happen at per-instruction granularity, which unlocks assembly code annotation. Ngl, currently the results can only be displayed by KCachegrind.
--compress-strings=<no|yes> [default: yes] — this one messes with the output format of the profile data. It decides whether strings (that's file and function names) get identified by numbers instead of spelled out. Shrinks the file, but makes it harder for humans to read — which, fr fr, is not recommended in any case. 😭
--compress-pos=<no|yes> [default: yes] — also an output-format influencer. It says whether numerical positions are always given as absolute values, or are allowed to be relative to previous numbers. Either way, the file gets smaller. 💖
--combine-dumps=<no|yes> [default: no] — when you enable this, and multiple profile data parts are gonna be generated, those parts get appended to the same output file. Not recommended. Periodt.
--dump-every-bb=<count> [default: 0, never] — dump profile data every count basic blocks. Okay so, whether a dump is even needed only gets checked when Valgrind's internal scheduler runs, so the minimum setting that's actually useful is around 100000. The count is a 64-bit value, which is what makes long dump periods possible. ⭐
--dump-before=<function> — dump when entering function.
--zero-before=<function> — zero all costs when entering function.
--dump-after=<function> — dump when leaving function.
--instr-atstart=<yes|no> [default: yes] — specify if you want Callgrind to start simulation and profiling from the beginning of the program. If you set it to no, Callgrind won't be able to collect any information — including calls — but it'll have at most a slowdown of around 4, which is the minimum Valgrind overhead. You can interactively enable instrumentation with callgrind_control -i on.

Just know that the resulting call graph will most probably not contain main, but will contain all the functions executed after instrumentation was enabled. Instrumentation can also be enabled/disabled programmatically — peep the Callgrind include file callgrind.h for the macro you have to use in your source code.

And for cache simulation? Results will be less accurate when you switch on instrumentation later in the program run, because the simulator starts with an empty cache at that exact moment. Switch on event collection later to cope with this error. 🦋

--collect-atstart=<yes|no> [default: yes] — specify whether event collection is enabled at the beginning of the profile run.

To only look at parts of your program, you've got two possibilities:

Zero event counters before entering the program part you want to profile, and dump the event counters to a file after leaving that program part.
Switch on/off collection state as needed, so you only see event counters happening while inside the program part you want to profile.

The second option is the move if the program part you wanna profile gets called many times — option 1, i.e. creating a lot of dumps, is just not practical here. 💀

Collection state can be toggled at entry and exit of a given function with the option --toggle-collect. If you use that option, collection state should be disabled at the beginning. Note that specifying --toggle-collect implicitly sets --collect-state=no.

Collection state can also be toggled by inserting the client request CALLGRIND_TOGGLE_COLLECT ; at the needed code positions.

--toggle-collect=<function> — toggle collection on entry/exit of function.
--collect-jumps=<no|yes> [default: no] — specifies whether information for (conditional) jumps should be collected. As above, callgrind_annotate currently is not able to show you the data. You have to use KCachegrind to get jump arrows in the annotated code. 🌈
--collect-systime=<no|yes|msec|usec|nsec> [default: no] — specifies whether information for system call times should be collected.

The value no means record no system call information at all, bestie.

The other values mean record the number of system calls done (the sysCount event) and the elapsed time (the sysTime event) spent in system calls. The --collect-systime value gives the unit used for sysTime: milli seconds, micro seconds or nano seconds. With the value nsec, callgrind also records the cpu time spent during system calls (sysCpuTime).

The value yes is a synonym of msec. And the value nsec is not supported on Darwin. 😤

--collect-bus=<no|yes> [default: no] — specifies whether the number of global bus events executed should be collected. The event type "Ge" is used for these events. 🔥
--cache-sim=<yes|no> [default: no] — specify if you want to do full cache simulation. By default, only instruction read accesses get counted ("Ir"). With cache simulation, further event counters are enabled: cache misses on instruction reads ("I1mr"/"ILmr"), data read accesses ("Dr") and related cache misses ("D1mr"/"DLmr"), data write accesses ("Dw") and related cache misses ("D1mw"/"DLmw"). For more info, see Cachegrind: a cache and branch-prediction profiler. ✨
--branch-sim=<yes|no> [default: no] — specify if you want to do branch prediction simulation. Further event counters get enabled: the number of executed conditional branches and related predictor misses ("Bc"/"Bcm"), plus executed indirect jumps and related misses of the jump address predictor ("Bi"/"Bim"). Slay. 💅

💅 HELGRIND OPTIONS 💅

okay bestie, this is the Helgrind section and it's long but we're gonna get through it together, i promise 🫶

--free-is-write=no|yes [default: no] — when you turn this ON (it's off by default, jsyk), Helgrind treats freeing heap memory as if the memory got written right before the free. why do we care? because it exposes races where one thread is out here referencing some memory while another thread is freeing it, and there's literally no observable synchronisation event guaranteeing the reference happens before the free. messy. 💀

this is new in Valgrind 3.7.0 and it's considered experimental — they're being so real about it. it's not on by default because how it interacts with custom memory allocators is "not well understood at present." user feedback is welcomed, so if you've got thoughts, speak up bestie ✨

--track-lockorders=no|yes [default: yes] — when enabled (which it is by default), Helgrind does lock order consistency checking. now, for some buggy programs the sheer number of lock order errors reported can get so annoying, especially if you only care about race errors. so yeah, you might find it helpful to just turn lock order checking off. no judgement 🎀
--history-level=none|approx|full [default: full]

okay so --history-level=full (the default) makes Helgrind collect enough info about "old" accesses that it can produce two stack traces in a race report — both the stack trace for the current access AND the trace for the older, conflicting access. to limit memory usage, "old" access stack traces are limited to a maximum of --history-backtrace-size entries (default 8) or to the --num-callers value if that value is smaller.

collecting all that info is expensive in both speed and memory, especially for programs that do a lot of inter-thread synchronisation events (locks, unlocks, etc). and without it, tracking down the root causes of races is way harder. but like — you may not need it when you just wanna check for the presence or absence of races, for example when doing regression testing on a previously race-free program.

--history-level=none is the opposite extreme. it makes Helgrind collect zero info about previous accesses. it can be dramatically faster than --history-level=full. slay for speed 💅

--history-level=approx is the compromise between those two extremes. it makes Helgrind show a full trace for the later access, plus approximate info about the earlier access. that approximate info is two stacks, and the earlier access is guaranteed to have happened somewhere between the program points denoted by those two stacks. it's not as useful as showing the exact stack for the previous access (like --history-level=full does), but it's better than nothing and it's almost as fast as --history-level=none. the middle child that ate 🍓

--history-backtrace-size=<number> [default: 8] — when --history-level=full is selected, --history-backtrace-size=number says how many entries to record in "old" accesses stack traces. 🧚
--delta-stacktrace=no|yes [default: yes on linux amd64/x86] — this flag only has any effect at --history-level=full.

--delta-stacktrace configures the way Helgrind captures the stacktraces for the option --history-level=full. such a stacktrace is typically needed each time a new piece of memory is read or written in a basic block of instructions.

--delta-stacktrace=no makes Helgrind compute a full history stacktrace from the unwind info each time a stacktrace is needed.

--delta-stacktrace=yes tells Helgrind to derive a new stacktrace from the previous stacktrace, as long as there was no call instruction, no return instruction, or any other instruction changing the call stack since the previous stacktrace was captured. if no such instruction was executed, the new stacktrace can be derived from the previous one just by changing the top frame to the current program counter. this option can speed up Helgrind by 25% when using --history-level=full. 🔥

the following aspects have to be considered when using --delta-stacktrace=yes:

in some cases (for example in a function prologue), the valgrind unwinder might not properly unwind the stack, due to some limitations and/or due to wrong unwind info. when using --delta-stacktrace=yes, the wrong stack trace captured in the function prologue will be kept till the next call or return. 😭
on the other hand, --delta-stacktrace=yes sometimes helps to obtain a correct stacktrace, for example when the unwind info allows a correct stacktrace to be done in the beginning of the sequence, but not later on in the instruction sequence.
determining which instructions are changing the callstack is partially based on platform dependent heuristics, which have to be tuned/validated specifically for the platform. also, unwinding in a function prologue must be good enough to allow using --delta-stacktrace=yes. currently, the option --delta-stacktrace=yes has been reasonably validated only on linux x86 32 bits and linux amd64 64 bits. for more details about how to validate --delta-stacktrace=yes, see debug option --hg-sanity-flags and the function check_cached_rcec_ok in libhb_core.c. iykyk 👑

--conflict-cache-size=N [default: 1000000] — this flag only has any effect at --history-level=full.

info about "old" conflicting accesses is stored in a cache of limited size, with LRU-style management. this is necessary because it isn't practical to store a stack trace for every single memory access the program makes. historical info on not-recently-accessed locations is periodically discarded, to free up space in the cache. spring cleaning but for memory bestie 🧹

this option controls the size of the cache, in terms of the number of different memory addresses for which conflicting access information is stored. if you find Helgrind is showing race errors with only one stack instead of the expected two stacks, try increasing this value.

the minimum value is 10,000 and the maximum is 30,000,000 (thirty times the default value). increasing the value by 1 increases Helgrind's memory requirement by very roughly 100 bytes, so the maximum value will easily eat up three extra gigabytes or so of memory. 💀 three gigabytes. be so fr.

--check-stack-refs=no|yes [default: yes] — by default Helgrind checks all data memory accesses your program makes. this flag lets you skip checking for accesses to thread stacks (local variables). it can improve performance, but at the cost of missing races on stack-allocated data. tradeoffs, we hate to see it 🙈
--ignore-thread-creation=<yes|no> [default: no] — controls whether all activities during thread creation should be ignored. by default it's enabled only on Solaris. Solaris provides higher throughput, parallelism and scalability than other operating systems, at the cost of more fine-grained locking activity. this means for example that when a thread is created under glibc, just one big lock is used for all thread setup. Solaris libc uses several fine-grained locks and the creator thread resumes its activities as soon as possible, leaving for example stack and TLS setup sequence to the created thread. this situation confuses Helgrind because it assumes there's some false ordering in place between creator and created thread — and therefore many types of race conditions in the application would not be reported. to prevent such false ordering, this command line option is set to yes by default on Solaris. all activity (loads, stores, client requests) is therefore ignored during:
- pthread_create() call in the creator thread
- thread creation phase (stack and TLS setup) in the created thread

also, new memory allocated during thread creation is untracked — meaning race reporting is suppressed there. DRD does the same thing implicitly. this is necessary because Solaris libc caches many objects and reuses them for different threads, and that confuses Helgrind. 🌸

--show-events=0|1|2 [default: 0] — controls tracing of internal Helgrind synchronization, threading and memory events. at level 1, Helgrind prints a trace of its synchronization, threading and memory events. at level 2, additional memory events are also traced. the default value of 0 disables tracing. ⭐
--track-destroy=no|yes|all [default: no] — controls checking for missing pthread_mutex_destroy and pthread_rwlock_destroy calls. with yes, Helgrind warns that a destroy call is missing when pthread_mutex_init or pthread_rwlock_init is called on an address that already has a live lock record. with all, Helgrind reports at process exit all mutexes and rwlocks that were explicitly initialized but never destroyed. locks that were not explicitly initialized (such as those using static initializers like PTHREAD_MUTEX_INITIALIZER) are not reported. the default value of no disables tracking. clean up after yourself bestie, it's giving self-care 💅✨

💖 DRD OPTIONS 💖

okay bestie, DRD time!! this is the data race detector tool and it has so many knobs to turn, but don't stress, we're gonna go through every single one together 🫶✨

--check-stack-var=<yes|no> [default: no] — this one controls whether DRD catches data races on stack variables. it's off by default because like… most programs are NOT out here sharing stack variables between threads, so checking them is kinda extra. if you turn it on, DRD will look at them too 💅
--exclusive-threshold=<n> [default: off] — if any mutex or writer lock has been held for longer than n milliseconds, DRD prints an error message at you. it's giving lock contention detection ✨
--join-list-vol=<n> [default: 10] — okay so here's the tea: when one thread joins another, if DRD throws away the memory access info immediately, it might miss data races happening between a statement at the end of one thread and another thread. this option lets you say how many joined threads should keep their memory access info retained 📝
--first-race-only=<yes|no> [default: no] — do you wanna hear about just the first data race detected on a memory location, or ALL of them?? your call, bestie 🌈
--free-is-write=<yes|no> [default: no] — should DRD report races between accessing memory and freeing memory?? turning this on might make DRD run slightly slower, ngl. and here are the notes, listen up:
- 🚨 do NOT enable this when you're using custom memory allocators that use VG_USERREQ__MALLOCLIKE_BLOCK and VG_USERREQ__FREELIKE_BLOCK, because that would give you false positives.
- 🚨 do NOT enable this when you're using reference-counted objects either, because that'll ALSO give you false positives — even when that code has been properly annotated with ANNOTATE_HAPPENS_BEFORE and ANNOTATE_HAPPENS_AFTER. wanna see an example?? the output of this command shows one:

valgrind --tool=drd --free-is-write=yes drd/tests/annotate_smart_pointer

--report-signal-unlocked=<yes|no> [default: yes] — this decides whether DRD reports calls to pthread_cond_signal and pthread_cond_broadcast where the mutex associated with the signal (through pthread_cond_wait or pthread_cond_timed_wait) is not locked at the time the signal gets sent. sending a signal without holding a lock on the associated mutex is a common programming error that can cause subtle race conditions and unpredictable behavior 😭 BUT — there are some uncommon synchronization patterns where it's actually safe to send a signal without holding that lock, so like, it's complicated 🫠
--segment-merging=<yes|no> [default: yes] — controls segment merging, which is an algorithm to limit memory usage of the data race detection algorithm. disabling it may improve the accuracy of the so-called 'other segments' shown in race reports, but it can also trigger an out of memory error 💀 so like, pick your poison
--segment-merging-interval=<n> [default: 10] — only do segment merging after this many new segments have been created. this is an advanced config option fr fr — pick a low value to minimize DRD's memory usage, or a slightly higher value to let DRD run faster. the optimal value depends on the program you're analyzing, bestie. the default works well for most programs tho ✨
--shared-threshold=<n> [default: off] — prints an error message if a reader lock has been held longer than the specified time (in milliseconds). this option enables lock contention detection 🎀
--show-confl-seg=<yes|no> [default: yes] — show conflicting segments in race reports. since this info can help you find the cause of a data race, it's on by default. disabling it makes DRD's output more compact, if you're into that 💅
--show-stack-usage=<yes|no> [default: no] — print stack usage at thread exit time. when a program creates a huge number of threads, limiting the virtual memory allocated for thread stacks becomes important. this option lets you observe how much stack memory each thread of the client program has used 👀 Note: the DRD tool itself allocates some temporary data on the client thread stack. the space needed for this temporary data must be allocated by the client program when it allocates stack memory, but it is not included in the stack usage reported by DRD 📌
--ignore-thread-creation=<yes|no> [default: no] — controls whether all activities during thread creation get ignored. by default it's enabled only on Solaris. so here's why: Solaris provides higher throughput, parallelism and scalability than other operating systems, at the cost of more fine-grained locking activity 🌞 this means, for example, that when a thread is created under glibc, just one big lock is used for all thread setup. Solaris libc uses several fine-grained locks and the creator thread resumes its activities ASAP, leaving like stack and TLS setup sequence to the created thread. this situation confuses DRD because it assumes there's some false ordering in place between creator and created thread — and therefore many types of race conditions in the application would not be reported 😱 to prevent that false ordering, this command line option is set to yes by default on Solaris. all activity (loads, stores, client requests) is therefore ignored during:
- pthread_create() call in the creator thread
- thread creation phase (stack and TLS setup) in the created thread
--trace-addr=<address> [default: none] — trace all load and store activity for the specified address 🔍 this option may be specified more than once!!
--ptrace-addr=<address> [default: none] — trace all load and store activity for the specified address AND keep doing that even after the memory at that address has been freed and reallocated 🕵️ persistent tracing, we love to see it
--trace-alloc=<yes|no> [default: no] — trace all memory allocations and deallocations. warning: may produce a HUGE amount of output 💀
--trace-barrier=<yes|no> [default: no] — trace all barrier activity 🚧
--trace-cond=<yes|no> [default: no] — trace all condition variable activity 🎀
--trace-fork-join=<yes|no> [default: no] — trace all thread creation and all thread termination events 🌱
--trace-hb=<yes|no> [default: no] — trace execution of the ANNOTATE_HAPPENS_BEFORE(), ANNOTATE_HAPPENS_AFTER() and ANNOTATE_HAPPENS_DONE() client requests ✨
--trace-mutex=<yes|no> [default: no] — trace all mutex activity 🔒
--trace-rwlock=<yes|no> [default: no] — trace all reader-writer lock activity 📖
--trace-semaphore=<yes|no> [default: no] — trace all semaphore activity 🚦

and that's the DRD options section, bestie!! we are SO not done yet tho, keep reading 💖

🌸 MASSIF OPTIONS 🌸

okay bestie, this is where Massif (the heap profiler, she's that girl) gets all her knobs and dials. buckle up 🎀

--heap=<yes|no> [default: yes] — says whether we're doing heap profiling at all. yes means yes 💅
--heap-admin=<size> [default: 8] — if heap profiling is on, this is how many administrative bytes per block to use. it's an estimate of the average (it can vary!), so don't come for it. for example, the allocator glibc uses on Linux needs somewhere between 4 to 15 bytes per block, depending on various factors. also that same allocator needs admin space for freed blocks too, but Massif literally cannot account for that. sorry babe 😭
--stacks=<yes|no> [default: no] — should we profile the stack? this option slows Massif down greatly, so yeah, it's off by default. also heads up: Massif assumes the main stack has size zero at start-up. that is not true, but doing otherwise accurately is difficult. plus, starting at zero actually better indicates the size of the part of the main stack that a user program actually has control over ✨

if you give at least 4 -v verbosity arguments, then massif produces a trace for each stack increase and decrease. the stack increase trace contains the IP address that increased the stack. note that to get a fully precise IP address, you must specify the options -px-default=unwindregs-at-mem-access --px-file-backed=unwindregs-at-mem-access.

--pages-as-heap=<yes|no> [default: no] — tells Massif to profile memory at the page level rather than at the malloc'd block level. see above for details 👀
--depth=<number> [default: 30] — the maximum depth of the allocation trees recorded for detailed snapshots. bumping it up makes Massif run somewhat more slowly, use more memory, and produce bigger output files. it's giving "bigger tree, bigger problems" 🌳
--alloc-fn=<name> — functions you name here get treated as though they were a heap allocation function, like malloc. this is useful for functions that are wrappers to malloc or new, which can fill up the allocation trees with uninteresting info. you can pass this option multiple times on the command line to name multiple functions. ✨

note that the named function will only be treated this way if it is the top entry in a stack trace, or just below another function treated this way. for example, if you have a function malloc1 that wraps malloc, and malloc2 that wraps malloc1, just specifying --alloc-fn=malloc2 will have no effect. you need to specify --alloc-fn=malloc1 as well. it's a little inconvenient, but the reason is that checking for allocation functions is slow, and it saves a lot of time if Massif can stop looking through the stack trace entries as soon as it finds one that doesn't match, rather than having to continue through all the entries. lowkey makes sense 🫶

note that C++ names are demangled. note also that overloaded C++ names must be written in full. single quotes may be necessary to prevent the shell from breaking them up. for example:

--alloc-fn='operator new(unsigned, std::nothrow_t const&)'

arguments of type size_t need to be replaced with unsigned long on 64bit platforms and unsigned on 32bit platforms.

--alloc-fn will work with inline functions. inline function names are not mangled, which means that you only need to provide the function name and not the argument list.

--alloc-fn does not support wildcards. 🚫

--ignore-fn=<name> — any direct heap allocation (i.e. a call to malloc, new, etc, or a call to a function named by an --alloc-fn option) that occurs in a function specified by this option will be ignored. this is mostly useful for testing purposes. you can pass this option multiple times on the command line to name multiple functions.

any realloc of an ignored block will also be ignored, even if the realloc call does not occur in an ignored function. this avoids the possibility of negative heap sizes if ignored blocks are shrunk with realloc. no negative heap sizes in this house 💀

the rules for writing C++ function names are the same as for --alloc-fn above.

--threshold=<m.n> [default: 1.0] — the significance threshold for heap allocations, as a percentage of total memory size. allocation tree entries that account for less than this get aggregated. note that this should be specified in tandem with ms_print's option of the same name 👯
--peak-inaccuracy=<m.n> [default: 1.0] — Massif does not necessarily record the actual global memory allocation peak; by default it records a peak only when the global memory allocation size exceeds the previous peak by at least 1.0%. this is because there can be many local allocation peaks along the way, and doing a detailed snapshot for every one would be expensive and wasteful, as all but one of them will be later discarded. you can change this inaccuracy (even to 0.0%) via this option, but Massif will run drastically slower as the number approaches zero. so like, choose wisely bestie 😭
--time-unit=<i|ms|B> [default: i] — the time unit used for the profiling. three possibilities, pick your fighter:
- instructions executed (i) — good for most cases ✨
- real (wallclock) time (ms, i.e. milliseconds) — sometimes useful
- bytes allocated/deallocated on the heap and/or stack (B) — useful for very short-run programs, and for testing purposes, because it is the most reproducible across different machines 👑
--detailed-freq=<n> [default: 10] — frequency of detailed snapshots. with --detailed-freq=1, every single snapshot is detailed. obsessed.
--max-snapshots=<n> [default: 100] — the maximum number of snapshots recorded. if set to N, for all programs except very short-running ones, the final number of snapshots will be between N/2 and N.
--massif-out-file=<file> [default: massif.out.%p] — write the profile data to file rather than to the default output file, massif.out.<pid>. the %p and %q format specifiers can be used to embed the process ID and/or the contents of an environment variable in the name, as is the case for the core option --log-file. 💖

🌈 BBV OPTIONS 🌈

basic block vector time, let's gooo 🦋

--bb-out-file=<name> [default: bb.out.%p] — this option selects the name of the basic block vector file. the %p and %q format specifiers can be used to embed the process ID and/or the contents of an environment variable in the name, as is the case for the core option --log-file.
--pc-out-file=<name> [default: pc.out.%p] — this option selects the name of the PC file. this file holds program counter addresses and function name info for the various basic blocks. this can be used in conjunction with the basic block vector file to fast-forward via function names instead of just instruction counts. the %p and %q format specifiers can be used to embed the process ID and/or the contents of an environment variable in the name, as is the case for the core option --log-file. 💅
--interval-size=<number> [default: 100000000] — this option selects the size of the interval to use. the default is 100 million instructions, which is a commonly used value. other sizes can be used; smaller intervals can help programs with finer-grained phases. however, smaller interval size can lead to accuracy issues due to warm-up effects (when fast-forwarding, the various architectural features will be un-initialized, and it will take some number of instructions before they "warm up" to the state a full simulation would be at without the fast-forwarding. large interval sizes tend to mitigate this.) it's giving "wake up babe, new architectural feature just dropped" 😴
--instr-count-only [default: no] — this option tells the tool to only display instruction count totals, and to not generate the actual basic block vector file. this is useful for debugging, and for gathering instruction count info without generating the large basic block vector files. small file, big knowledge ✨

💀 LACKEY OPTIONS 💀

Lackey is the silly little minimal tool and honestly? iconic.

--basic-counts=<no|yes> [default: yes] — when enabled, Lackey prints the following statistics and information about the execution of the client program:
1. the number of calls to the function specified by the --fnname option (the default is main). if the program has had its symbols stripped, the count will always be zero. 🙈
2. the number of conditional branches encountered and the number and proportion of those taken.
3. the number of superblocks entered and completed by the program. note that due to optimisations done by the JIT, this is not at all an accurate value.
4. the number of guest (x86, amd64, ppc, etc.) instructions and IR statements executed. IR is Valgrind's RISC-like intermediate representation via which all instrumentation is done.
5. ratios between some of these counts.
6. the exit code of the client program.
--detailed-counts=<no|yes> [default: no] — when enabled, Lackey prints a table containing counts of loads, stores and ALU operations, differentiated by their IR types. the IR types are identified by their IR name ("I1", "I8", ... "I128", "F32", "F64", and "V128"). 📊
--trace-mem=<no|yes> [default: no] — when enabled, Lackey prints the size and address of almost every memory access made by the program. see the comments at the top of the file lackey/lk_main.c for details about the output format, how it works, and inaccuracies in the address trace. note that this option produces immense amounts of output. like, your terminal will be fighting for its life 😭
--trace-superblocks=<no|yes> [default: no] — when enabled, Lackey prints out the address of every superblock (a single entry, multiple exit, linear chunk of code) executed by the program. this is primarily of interest to Valgrind developers. see the comments at the top of the file lackey/lk_main.c for details about the output format. note that this option produces large amounts of output. ‼️
--fnname=<name> [default: main] — changes the function for which calls are counted when --basic-counts=yes is specified. 🎀

🧚 DEBUGINFOD 🧚

okay so Valgrind supports the downloading of debuginfo files via debuginfod, an HTTP server for distributing ELF/DWARF debugging information. when a debuginfo file cannot be found locally, Valgrind is able to query debuginfod servers for the file using the file's build-id. the way that it just finds it? slay.

in order to use this feature, debuginfod-find must be installed and the $DEBUGINFOD_URLS environment variable must contain space-separated URLs of debuginfod servers. Valgrind does not support debuginfod-find verbose output that is normally enabled with $DEBUGINFOD_PROGRESS and $DEBUGINFOD_VERBOSE. these environment variables will be ignored. 🙅 this feature is supported on Linux only.

for more information regarding debuginfod, see Elfutils Debuginfod[1] . 💜

🦋 SEE ALSO 🦋

okay bestie, when you're done vibing with Valgrind itself, here's the whole little friend group you're gonna wanna meet 💖

cg_annotate(1)
callgrind_annotate(1)
callgrind_control(1)
ms_print(1)
$INSTALL/share/doc/valgrind/html/index.html or http://www.valgrind.org/docs/manual/index.html
Debugging your program using Valgrind's gdbserver and GDB [2]
vgdb [3]
Valgrind monitor commands [4]
The Commentary [5]
Scheduling and Multi-Thread Performance [6]
Cachegrind: a cache and branch-prediction profiler [7]
Execution Trees [8]

👑 AUTHOR 👑

want the full roster of everyone who made this happen? go peep the AUTHORS file in the valgrind distribution — it's the comprehensive list, no one left out 🫶

This manpage was written by Andres Roldan <aroldan@debian.org> and the Valgrind developers.

📝 NOTES 📝

Elfutils Debuginfod — https://sourceware.org/elfutils/Debuginfod.html
Debugging your program using Valgrind's gdbserver and GDB — http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.gdbserver
vgdb — http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.vgdb
Valgrind monitor commands — http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.valgrind-monitor-commands
The Commentary — http://www.valgrind.org/docs/manual/manual-core.html#manual-core.comment
Scheduling and Multi-Thread Performance — http://www.valgrind.org/docs/manual/manual-core.html#manual-core.pthreads_perf_sched
Cachegrind: a cache and branch-prediction profiler — http://www.valgrind.org/docs/manual/cg-manual.html
Execution Trees — http://www.valgrind.org/docs/manual/manual-core.html#manual-core.xtree

and that's a wrap on the whole entire manpage, bestie 💅✨ that was Release 3.27.1, dated 09/09/2026 — slay, iconique, no notes, periodt 🎀🦋💖

📦 where this page comes from

ubuntu stonking: valgrind 1:3.27.1-0.2ubuntu2 · GPL-3.0-or-later
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms

VALGRIND(1)

💅 valgrind(1) — bestie edition 💅

✨ NAME ✨

✨ SYNOPSIS ✨

✨ DESCRIPTION ✨

🎀 TOOL SELECTION OPTIONS 🎀

🌈 BASIC OPTIONS 🌈

🌈 ERROR-RELATED OPTIONS 🌈

🧸 MALLOC()-RELATED OPTIONS 🧸

🌀 UNCOMMON OPTIONS 🌀

--merge-recursive-frames=<number> [default: 0]

--num-transtab-sectors=<number> [default: 6 for Android platforms, 16 for all others]

--avg-transtab-entry-size=<number> [default: 0, meaning use tool provided default]

--aspace-minaddr=<address> [default: depends on the platform]

--valgrind-stacksize=<number> [default: 1MB]

--show-emwarns=<yes|no> [default: no]

--require-text-symbol=:sonamepatt:fnnamepatt

--soname-synonyms=syn1=pattern1,syn2=pattern2,...

--progress-interval=<number> [default: 0, meaning 'disabled']