OBJCOPY(1)

📦
version 2.40.50~ti1ubuntu1 · 2 versions
, in ubuntu noble

💖 NAME 💖

Okay so bestie, welcome to the OBJCOPY(1) manual page! It's literally all about objcopy — copy and translate object files. That's the whole main character energy right there. ✨

🌸 SYNOPSIS 🌸

       objcopy [-F bfdname|--target=bfdname]
               [-I bfdname|--input-target=bfdname]
               [-O bfdname|--output-target=bfdname]
               [-B bfdarch|--binary-architecture=bfdarch]
               [-S|--strip-all]
               [-g|--strip-debug]
               [--strip-unneeded]
               [-K symbolname|--keep-symbol=symbolname]
               [--keep-file-symbols]
               [--keep-section-symbols]
               [-N symbolname|--strip-symbol=symbolname]
               [--strip-unneeded-symbol=symbolname]
               [-G symbolname|--keep-global-symbol=symbolname]
               [--localize-hidden]
               [-L symbolname|--localize-symbol=symbolname]
               [--globalize-symbol=symbolname]
               [--globalize-symbols=filename]
               [-W symbolname|--weaken-symbol=symbolname]
               [-w|--wildcard]
               [-x|--discard-all]
               [-X|--discard-locals]
               [-b byte|--byte=byte]
               [-i [breadth]|--interleave[=breadth]]
               [--interleave-width=width]
               [-j sectionpattern|--only-section=sectionpattern]
               [-R sectionpattern|--remove-section=sectionpattern]
               [--keep-section=sectionpattern]
               [--remove-relocations=sectionpattern]
               [--strip-section-headers]
               [-p|--preserve-dates]
               [-D|--enable-deterministic-archives]
               [-U|--disable-deterministic-archives]
               [--debugging]
               [--gap-fill=val]
               [--pad-to=address]
               [--set-start=val]
               [--adjust-start=incr]
               [--change-addresses=incr]
               [--change-section-address sectionpattern{=,+,-}val]
               [--change-section-lma sectionpattern{=,+,-}val]
               [--change-section-vma sectionpattern{=,+,-}val]
               [--change-warnings] [--no-change-warnings]
               [--set-section-flags sectionpattern=flags]
               [--set-section-alignment sectionpattern=align]
               [--add-section sectionname=filename]
               [--dump-section sectionname=filename]
               [--update-section sectionname=filename]
               [--rename-section oldname=newname[,flags]]
               [--long-section-names {enable,disable,keep}]
               [--change-leading-char] [--remove-leading-char]
               [--reverse-bytes=num]
               [--srec-len=ival] [--srec-forceS3]
               [--redefine-sym old=new]
               [--redefine-syms=filename]
               [--weaken]
               [--keep-symbols=filename]
               [--strip-symbols=filename]
               [--strip-unneeded-symbols=filename]
               [--keep-global-symbols=filename]
               [--localize-symbols=filename]
               [--weaken-symbols=filename]
               [--add-symbol name=[section:]value[,flags]]
               [--alt-machine-code=index]
               [--prefix-symbols=string]
               [--prefix-sections=string]
               [--prefix-alloc-sections=string]
               [--add-gnu-debuglink=path-to-file]
               [--only-keep-debug]
               [--strip-dwo]
               [--extract-dwo]
               [--extract-symbol]
               [--writable-text]
               [--readonly-text]
               [--pure]
               [--impure]
               [--file-alignment=num]
               [--heap=size]
               [--image-base=address]
               [--section-alignment=num]
               [--stack=size]
               [--subsystem=which:major.minor]
               [--compress-debug-sections]
               [--decompress-debug-sections]
               [--elf-stt-common=val]
               [--merge-notes]
               [--no-merge-notes]
               [--verilog-data-width=val]
               [-v|--verbose]
               [-V|--version]
               [--help] [--info]
               infile [outfile]

🦋 DESCRIPTION 🦋

So the GNU objcopy utility is out here copying the contents of an object file to another one. It uses the GNU BFD Library to read and write those object files, and it can write the destination object file in a format that's totally different from the source. The exact behavior? Controlled by command-line options, obviously. 💅

Note bestie: objcopy should be able to copy a fully linked file between any two formats. But copying a relocatable object file between any two formats may not work as expected. So don't come for me if that acts up. 😭

It creates temporary files to do its translations and deletes them afterward. It uses BFD to do all its translation work; it has access to all the formats described in BFD and thus is able to recognize most formats without being told explicitly. No cap.

You can use objcopy to generate S-records by using an output target of srec (e.g., use -O srec). Slay.

You can also use it to generate a raw binary file by using an output target of binary (e.g., use -O binary). When objcopy generates a raw binary file, it will essentially produce a memory dump of the contents of the input object file. All symbols and relocation information will be discarded. The memory dump will start at the load address of the lowest section copied into the output file. It's giving memory dump realness.

When generating an S-record or a raw binary file, it may be helpful to use -S to remove sections containing debugging information. In some cases -R will be useful to remove sections which contain information that is not needed by the binary file. Iconic.

Note: objcopy is not able to change the endianness of its input files. If the input format has an endianness (some formats do not), objcopy can only copy the inputs into file formats that have the same endianness or which have no endianness (e.g., srec). (However, see the --reverse-bytes option.) So don't try it. 💀

💅 OPTIONS 💅

Okay bestie, here's the tea on every option in this part. ☕

  • infile, outfile — The input and output files, respectively. If you do not specify outfile, objcopy creates a temporary file and destructively renames the result with the name of infile. So it's like a glow-up in place. ✨
  • -I bfdname, --input-target=bfdname — Consider the source file's object format to be bfdname, rather than attempting to deduce it. Just tell it what's up. 💁‍♀️
  • -O bfdname, --output-target=bfdname — Write the output file using the object format bfdname. That's the output vibe.
  • -F bfdname, --target=bfdname — Use bfdname as the object format for both the input and the output file; i.e., simply transfer data from source to destination with no translation. It's giving copy-paste, no changes. 🫶
  • -B bfdarch, --binary-architecture=bfdarch — Useful when transforming a architecture-less input file into an object file. In this case the output architecture can be set to bfdarch. This option will be ignored if the input file has a known bfdarch. You can access this binary data inside a program by referencing the special symbols that are created by the conversion process. These symbols are called _binary_objfile_start, _binary_objfile_end and _binary_objfile_size. e.g. you can transform a picture file into an object file and then access it in your code using these symbols. So you can flex that image data in your C code. 📸
  • -j sectionpattern, --only-section=sectionpattern — Copy only the indicated sections from the input file to the output file. This option may be given more than once. Note that using this option inappropriately may make the output file unusable. Wildcard characters are accepted in sectionpattern. ⚠️

If the first character of sectionpattern is the exclamation point (!) then matching sections will not be copied, even if earlier use of --only-section on the same command line would otherwise copy it. For example:

--only-section=.text.* --only-section=!.text.foo

will copy all sections matching .text.* but not the section .text.foo. So it's like a VIP list with a blacklist. 💅

  • -R sectionpattern, --remove-section=sectionpattern — Remove any section matching sectionpattern from the output file. This option may be given more than once. Note that using this option inappropriately may make the output file unusable. Wildcard characters are accepted in sectionpattern. Using both the -j and -R options together results in undefined behaviour. So don't do that. 🚫

If the first character of sectionpattern is the exclamation point (!) then matching sections will not be removed even if an earlier use of --remove-section on the same command line would otherwise remove it. For example:

--remove-section=.text.* --remove-section=!.text.foo

will remove all sections matching the pattern .text.*, but will not remove the section .text.foo. So it's like a bouncer that lets one section back in. 😌

  • --keep-section=sectionpattern — When removing sections from the output file, keep sections that match sectionpattern. It's the "you can stay" option. 🥰
  • --remove-relocations=sectionpattern — Remove non-dynamic relocations from the output file for any section matching sectionpattern. This option may be given more than once. Note that using this option inappropriately may make the output file unusable, and attempting to remove a dynamic relocation section such as .rela.plt from an executable or shared library with --remove-relocations=.plt will not work. Wildcard characters are accepted in sectionpattern. For example:
--remove-relocations=.text.*

will remove the relocations for all sections matching the pattern .text.*. So it's like cleaning up the clutter. 🧹

If the first character of sectionpattern is the exclamation point (!) then matching sections will not have their relocation removed even if an earlier use of --remove-relocations on the same command line would otherwise cause the relocations to be removed. For example:

--remove-relocations=.text.* --remove-relocations=!.text.foo

will remove all relocations for sections matching the pattern .text.*, but will not remove relocations for the section .text.foo. So it's a protection spell for .text.foo. ✨

  • --strip-section-headers — Strip section header. This option is specific to ELF files. Implies --strip-all and --merge-notes. It's giving minimalism. 💀
  • -S, --strip-all — Do not copy relocation and symbol information from the source file. Also deletes debug sections. It's the full clear-out. 🗑️
  • -g, --strip-debug — Do not copy debugging symbols or sections from the source file. Just the debug stuff gets yeeted. 🙈
  • --strip-unneeded — Remove all symbols that are not needed for relocation processing in addition to debugging symbols and sections stripped by --strip-debug. So it's extra thorough. 🔥
  • -K symbolname, --keep-symbol=symbolname — When stripping symbols, keep symbol symbolname even if it would normally be stripped. This option may be given more than once. It's the "not you, you stay" option. 🫶
  • -N symbolname, --strip-symbol=symbolname — Do not copy symbol symbolname from the source file. This option may be given more than once. So it's the "you gotta go" option. 👋
  • --strip-unneeded-symbol=symbolname — Do not copy symbol symbolname from the source file unless it is needed by a relocation. This option may be given more than once. So it's like "you can stay only if you're useful". 💅
  • -G symbolname, --keep-global-symbol=symbolname — okay so this one keeps only symbolname global. Everything else? It makes all other symbols local to the file, so they're not visible externally. You can drop this option more than once if you want. Note: this option cannot be used in conjunction with the --globalize-symbol or --globalize-symbols options. 🫶
  • --localize-hidden — in an ELF object, mark all symbols that have hidden or internal visibility as local. This option applies on top of symbol-specific localization options such as -L. it's giving stealth mode ✨
  • -L symbolname, --localize-symbol=symbolname — convert a global or weak symbol called symbolname into a local symbol, so it's not visible externally. you can use this more than once. Note unique symbols are not converted. 💅
  • -W symbolname, --weaken-symbol=symbolname — make symbol symbolname weak. This option may be given more than once. weak like my motivation on a Monday 😭
  • --globalize-symbol=symbolname — give symbol symbolname global scoping so it's visible outside of the file in which it is defined. This option may be given more than once. Note: this option cannot be used in conjunction with the -G or --keep-global-symbol options. 👑
  • -w, --wildcard — permit regular expressions in symbolnames used in other command line options. The question mark (?), asterisk (*), backslash (\) and square brackets ([]) operators can be used anywhere in the symbol name. If the first character of the symbol name is the exclamation point (!) then the sense of the switch is reversed for that symbol. For example:
-w -W !foo -W fo*

would cause objcopy to weaken all symbols that start with "fo" except for the symbol "foo". regex slay 🦋

  • -x, --discard-all — do not copy non-global symbols from the source file. bye bye local faves 👋
  • -X, --discard-locals — do not copy compiler-generated local symbols. (These usually start with L or ..) compiler cooties, we don't want them 🙈
  • -b byte, --byte=byte — if interleaving has been enabled via the --interleave option then start the range of bytes to keep at the byteth byte. byte can be in the range from 0 to breadth-1, where breadth is the value given by the --interleave option. math but make it cute 🎀
  • -i [breadth], --interleave[=breadth] — only copy a range out of every breadth bytes. (Header data is not affected). Select which byte in the range begins the copy with the --byte option. Select the width of the range with the --interleave-width option.

This option is useful for creating files to program ROM. It is typically used with an "srec" output target. Note that objcopy will complain if you do not specify the --byte option as well.

The default interleave breadth is 4, so with --byte set to 0, objcopy would copy the first byte out of every four bytes from the input to the output. ROM era bestie 🔥

  • --interleave-width=width — when used with the --interleave option, copy width bytes at a time. The start of the range of bytes to be copied is set by the --byte option, and the extent of the range is set with the --interleave option.

The default value for this option is 1. The value of width plus the byte value set by the --byte option must not exceed the interleave breadth set by the --interleave option.

This option can be used to create images for two 16-bit flashes interleaved in a 32-bit bus by passing -b 0 -i 4 --interleave-width=2 and -b 2 -i 4 --interleave-width=2 to two objcopy commands. If the input was '12345678' then the outputs would be '1256' and '3478' respectively. interleaving ate and left no crumbs 💅

  • -p, --preserve-dates — set the access and modification dates of the output file to be the same as those of the input file. time travel but make it file metadata ⏳
  • -D, --enable-deterministic-archives — operate in deterministic mode. When copying archive members and writing the archive index, use zero for UIDs, GIDs, timestamps, and use consistent file modes for all files.

If binutils was configured with --enable-deterministic-archives, then this mode is on by default. It can be disabled with the -U option, below. reproducible vibes ✨

  • -U, --disable-deterministic-archives — do not operate in deterministic mode. This is the inverse of the -D option, above: when copying archive members and writing the archive index, use their actual UID, GID, timestamp, and file mode values.

This is the default unless binutils was configured with --enable-deterministic-archives. keep it real 🫶

  • --debugging — convert debugging information, if possible. This is not the default because only certain debugging formats are supported, and the conversion process can be time consuming. debugging but make it extra 🐛
  • --gap-fill val — fill gaps between sections with val. This operation applies to the load address (LMA) of the sections. It is done by increasing the size of the section with the lower address, and filling in the extra space created with val. filling the void, literally 🕳️
  • --pad-to address — pad the output file up to the load address address. This is done by increasing the size of the last section. The extra space is filled in with the value specified by --gap-fill (default zero). padding like a cute lil cushion 🛋️
  • --set-start val — set the start address (also known as the entry address) of the new file to val. Not all object file formats support setting the start address. where the party starts 🎉
  • --change-start incr, --adjust-start incr — change the start address (also known as the entry address) by adding incr. Not all object file formats support setting the start address. shift it, but not all formats are invited 🕺
  • --change-addresses incr, --adjust-vma incr — change the VMA and LMA addresses of all sections, as well as the start address, by adding incr. Some object file formats do not permit section addresses to be changed arbitrarily. Note that this does not relocate the sections; if the program expects sections to be loaded at a certain address, and this option is used to change the sections such that they are loaded at a different address, the program may fail. danger danger 💀
  • --change-section-address sectionpattern{=,+,-}val, --adjust-section-vma sectionpattern{=,+,-}val — set or change both the VMA address and the LMA address of any section matching sectionpattern. If = is used, the section address is set to val. Otherwise, val is added to or subtracted from the section address. See the comments under --change-addresses, above. If sectionpattern does not match any sections in the input file, a warning will be issued, unless --no-change-warnings is used. pattern matching but make it address magic ✨
  • --change-section-lma sectionpattern{=,+,-}val — set or change the LMA address of any sections matching sectionpattern. The LMA address is the address where the section will be loaded into memory at program load time. Normally this is the same as the VMA address, which is the address of the section at program run time, but on some systems, especially those where a program is held in ROM, the two can be different. If = is used, the section address is set to val. Otherwise, val is added to or subtracted from the section address. See the comments under --change-addresses, above. If sectionpattern does not match any sections in the input file, a warning will be issued, unless --no-change-warnings is used. load time address, not runtime address, bestie 🧠
  • --change-section-vma sectionpattern{=,+,-}val — set or change the VMA address of any section matching sectionpattern. The VMA address is the address where the section will be located once the program has started executing. Normally this is the same as the LMA address, which is the address where the section will be loaded into memory, but on some systems, especially those where a program is held in ROM, the two can be different. If = is used, the section address is set to val. Otherwise, val is added to or subtracted from the section address. See the comments under --change-addresses, above. If sectionpattern does not match any sections in the input file, a warning will be issued, unless --no-change-warnings is used. runtime address, the main character energy 👑
  • --change-warnings, --adjust-warnings — if --change-section-address or --change-section-lma or --change-section-vma is used, and the section pattern does not match any sections, issue a warning. This is the default. warning bestie, it's on by default ⚠️
  • --no-change-warnings, --no-adjust-warnings — do not issue a warning if --change-section-address or --adjust-section-lma or --adjust-section-vma is used, even if the section pattern does not match any sections. silence is golden 🤫
  • --set-section-flags sectionpattern=flags — set the flags for any sections matching sectionpattern. The flags argument is a comma separated string of flag names. The recognized names are alloc, contents, load, noload, readonly, code, data, rom, exclude, share, and debug. You can set the contents flag for a section which does not have contents, but it is not meaningful to clear the contents flag of a section which does have contents--just remove the section instead. Not all flags are meaningful for all object file formats. In particular the share flag is only meaningful for COFF format files and not for ELF format files. flags, flags, flags 🏳️
  • --set-section-alignment sectionpattern=align — set the alignment for any sections matching sectionpattern. align specifies the alignment in bytes and must be a power of two, i.e. 1, 2, 4, 8.... power of two or it's not invited 🔢
  • --add-section sectionname=filename — add a new section named sectionname while copying the file. The contents of the new section are taken from the file filename. The size of the section will be the size of the file. This option only works on file formats which can support sections with arbitrary names. Note - it may be necessary to use the --set-section-flags option to set the attributes of the newly created section. new section, who dis? 🆕
  • --dump-section sectionname=filename — place the contents of section named sectionname into the file filename, overwriting any contents that may have been there previously. This option is the inverse of --add-section. This option is similar to the --only-section option except that it does not create a formatted file, it just dumps the contents as raw binary data, without applying any relocations. The option can be specified more than once. raw dump, no formatting, just vibes 🗑️
  • --update-section sectionname=filename — okay so this one replaces the whole contents of the section called sectionname with whatever's in the file filename 🫶. The section resizes itself to match the file's size, no cap. But bestie, the section flags for sectionname? Untouched. Unchanged. Iconic. And for ELF format files the section-to-segment mapping also stays exactly the same — which is a whole thing you literally cannot pull off by doing --remove-section and then --add-section, so jot that down 💅. You can drop this option on the command line more than once, go off.
    • Real talk though: you can use --rename-section and --update-section together to update and rename a section from one single command line ✨. The way that works is: you pass the original section name to --update-section, and then the original and new section names to --rename-section. That's the move.
  • --add-symbol name=[section:]value[,flags] — adds a brand new symbol called name while it's copying the file 🎀. Specify it multiple times if you want, no judgment. If you give a section, the symbol gets associated with that section and becomes relative to it — otherwise it's an ABS symbol, periodt. Give it a section that doesn't exist and you get a fatal error 💀. Also there's literally no check on the value, it just takes it exactly as you typed it. Symbol flags? Yeah you can pass those, but not every flag is meaningful for every object file format, so vibe check accordingly. By default the symbol is global. And the special flag 'before=othersym' inserts your new symbol right in front of the specified othersym — otherwise the symbol(s) get tacked onto the end of the symbol table in the order they appear. Slay.
  • --rename-section oldname=newname[,flags] — renames a section from oldname to newname, and optionally swaps the section's flags to flags while it's at it 🌸. The glow-up here vs. using a linker script to do the rename is that your output stays an object file and does not become a linked executable. It accepts the same set of flags as the --sect-section-flags option. Obsessed.
    • This one is particularly helpful when your input format is binary, because that always creates a section called .data 🙈. So say you wanted a section called .rodata holding binary data instead — here's the command line that gets you there:
objcopy -I binary -O <output_format> -B <architecture> \
 --rename-section .data=.rodata,alloc,load,readonly,data,contents \
 <input_binary_file> <output_object_file>
  • --long-section-names {enable,disable,keep} — this controls how long section names get handled when you're processing "COFF" and "PE-COFF" object formats 🦋. The default behaviour, keep, preserves long section names if any are present in the input file. enable and disable forcibly turn the use of long section names on or off in the output object; when disable is in effect, any long section names in the input object get truncated 😭. The enable option will only emit long section names if any are present in the inputs — mostly the same as keep, but it is left undefined whether enable might force the creation of an empty string table in the output file. Undefined! Not a vibe, just a fact.
  • --change-leading-char — some object file formats use special characters at the start of symbols ⭐. The most common one is underscore, which compilers love to slap in front of every single symbol. This option tells objcopy to change the leading character of every symbol when it converts between object file formats. If both formats use the same leading character, this option does absolutely nothing, zero effect, it's giving no-op. Otherwise it'll add a character, or remove a character, or change a character, as appropriate 💅.
  • --remove-leading-char — if the first character of a global symbol is a special symbol leading character used by the object file format, remove it ✂️. The most common symbol leading character is underscore. So this option will strip a leading underscore off all global symbols. Useful if you wanna link together objects of different file formats that have different conventions for symbol names. And heads up, this is different from --change-leading-char because it always changes the symbol name when appropriate, regardless of the object file format of the output file. Not the same thing bestie, don't mix them up 🫶.
  • --reverse-bytes=num — reverses the bytes in a section with output contents 🔥. For the swap to even be able to happen, a section's length must be evenly divisible by the value you gave. And reversing takes place before the interleaving is performed, so order matters.
    • This option is typically used when generating ROM images for problematic target systems. For example, on some target boards, the 32-bit words fetched from 8-bit ROMs get re-assembled in little-endian byte order regardless of the CPU byte order 😵. Depending on the programming model, the endianness of the ROM may need to be modified.
    • Consider a simple file with a section containing the following eight bytes: 12345678.
    • Using --reverse-bytes=2 for the above example, the bytes in the output file would be ordered 21436587.
    • Using --reverse-bytes=4 for the above example, the bytes in the output file would be ordered 43218765.
    • By using --reverse-bytes=2 for the above example, followed by --reverse-bytes=4 on the output file, the bytes in the second output file would be ordered 34127856.
  • --srec-len=ival — meaningful only for srec output 💜. Sets the maximum length of the Srecords being produced to ival. This length covers both address, data and crc fields, so all of it.
  • --srec-forceS3 — also meaningful only for srec output 🌈. Avoids generation of S1/S2 records, creating an S3-only record format. Only S3. Nothing else. Periodt.
  • --redefine-sym old=new — changes the name of a symbol old to new ✨. Genuinely useful when you're trying to link two things together, you have no source for either, and the names are colliding. Classic.
  • --redefine-syms=filename — applies --redefine-sym to each symbol pair "old new" listed in the file filename 🎀. filename is just a flat file with one symbol pair per line. Line comments may be introduced by the hash character. And yeah, you can give this option more than once.
  • --weaken — changes all global symbols in the file to be weak 🦋. Handy when you're building an object that'll be linked against other objects using the -R option to the linker. Fair warning: this option is only effective when you're using an object file format that actually supports weak symbols.
  • --keep-symbols=filename — applies --keep-symbol to each symbol listed in the file filename 💖. filename is a flat file with one symbol name per line. Line comments may be introduced by the hash character. May be given more than once.
  • --strip-symbols=filename — applies --strip-symbol to each symbol listed in the file filename 💅. filename is a flat file with one symbol name per line. Line comments may be introduced by the hash character. May be given more than once.
  • --strip-unneeded-symbols=filename — applies --strip-unneeded-symbol to each symbol listed in the file filename 🌸. filename is a flat file with one symbol name per line. Line comments may be introduced by the hash character. May be given more than once.
  • --keep-global-symbols=filename — applies --keep-global-symbol to each symbol listed in the file filename 👑. filename is a flat file with one symbol name per line. Line comments may be introduced by the hash character. May be given more than once.
  • --localize-symbols=filename — applies --localize-symbol to each symbol listed in the file filename ⭐. filename is a flat file with one symbol name per line. Line comments may be introduced by the hash character. May be given more than once.
  • --globalize-symbols=filename — applies --globalize-symbol to each symbol listed in the file filename 🔥. filename is a flat file with one symbol name per line. Line comments may be introduced by the hash character. May be given more than once.
    • > Note: this option cannot be used in conjunction with the -G or --keep-global-symbol options. They do not get along, it's giving enemies to lovers but only the enemies part 💀.
  • --weaken-symbols=filename — applies --weaken-symbol to each symbol listed in the file filename 🧚. filename is a flat file with one symbol name per line. Line comments may be introduced by the hash character. May be given more than once.
  • --alt-machine-code=index — if the output architecture has alternate machine codes, use the indexth code instead of the default one 🙈. Useful in case a machine gets assigned an official code and the tool-chain adopts the new code, but other applications still depend on the original code being used. And for ELF based architectures, if the index alternative does not exist then the value is treated as an absolute number to be stored in the e_machine field of the ELF header. Wild but true.
  • --writable-text — marks the output text as writable ✍️. This option isn't meaningful for all object file formats, so don't be surprised if some formats just ignore you.
  • --readonly-text — makes the output text write protected 🔒. Again, this option isn't meaningful for all object file formats.
  • --pure — marks the output file as demand paged ✨. This option isn't meaningful for all object file formats.
  • --impure — marks the output file as impure 😈. This option isn't meaningful for all object file formats.
  • --prefix-symbols=string — prefixes all symbols in the output file with string 🎀.
  • --prefix-sections=string — prefixes all section names in the output file with string 💖.
  • --prefix-alloc-sections=string — prefixes all the names of all allocated sections in the output file with string 🌈.
  • --add-gnu-debuglink=path-to-file — creates a .gnu_debuglink section that contains a reference to path-to-file, and adds it to the output file 🦋.
    • > Note: the file at path-to-file must exist. Non-negotiable. Part of the process of adding the .gnu_debuglink section involves embedding a checksum of the contents of the debug info file into the section.
    • Okay so listen: if the debug info file is built in one location but it's going to be installed at a later time into a different location, then do not use the path to the installed location 😭. The --add-gnu-debuglink option will fail because the installed file does not exist yet. Instead, put the debug info file in the current directory and use the --add-gnu-debuglink option without any directory components, like this:
objcopy --add-gnu-debuglink=foo.debug

At debug time the debugger goes hunting for that separate debug info file in a bunch of known spots. The exact list depends on your distro, but it's usually something like:

  • The same directory as the executable.
  • A sub-directory of the directory containing the executable, called .debug
  • A global debug directory like /usr/lib/debug.

So as long as you've dropped the debug info file into one of those places before you run the debugger, everything just works. ✨

  • --keep-section-symbils — okay so when you're stripping a file (say with --strip-debug or --strip-unneeded), this keeps any symbols that specify section names. Those would otherwise get yeeted along with everything else. 🫶
  • --keep-file-symbols — same energy but for source file names: while stripping (again, --strip-debug or --strip-unneeded), retain any symbols specifying source file names that would otherwise get stripped.
  • --only-keep-debug — this one strips a file but removes the contents of any sections that --strip-debug wouldn't strip, and leaves the debugging sections fully intact. In ELF files it preserves all note sections in the output. 👑
Note: the section headers of the stripped sections are preserved, sizes and all, but the actual contents of the section get discarded. Why keep the headers? So other tools can match up the debuginfo file with the real executable — even if that executable has been relocated to a totally different address space. iconic behavior honestly.

The whole intention here is that you use this alongside --add-gnu-debuglink to build a two-part executable. Part one: a stripped binary that takes up less space in RAM and in a distribution. Part two: a debugging information file that you only need if you actually want to debug. The suggested procedure is:

  1. Link the executable as normal. Assuming it's called foo then...
  2. Run objcopy --only-keep-debug foo foo.dbg to create a file containing the debugging info.
  3. Run objcopy --strip-debug foo to create a stripped executable.
  4. Run objcopy --add-gnu-debuglink=foo.dbg foo to add a link to the debugging info into the stripped executable.
Note: the choice of .dbg as an extension is arbitrary, bestie. And the --only-keep-debug step is optional too. You could instead do this:
  1. Link the executable as normal.
  2. Copy foo to foo.full
  3. Run objcopy --strip-debug foo
  4. Run objcopy --add-gnu-debuglink=foo.full foo

i.e., the file pointed to by --add-gnu-debuglink can be the full executable. It does not have to be a file created by the --only-keep-debug switch. 💅

Note: this switch is only intended for use on fully linked files. It does not make sense to use it on object files where the debugging information may be incomplete. Also, the gnu_debuglink feature currently only supports the presence of one filename containing debugging information — not multiple filenames on a one-per-object-file basis. 🙈
  • --strip-dwo — removes the contents of all DWARF .dwo sections, leaving the remaining debugging sections and all symbols intact. This one is meant to be used by the compiler as part of the -gsplit-dwarf option, which splits debug info between the .o file and a separate .dwo file. The compiler generates all the debug information in the same file, then uses --extract-dwo to copy the .dwo sections into the .dwo file, then uses --strip-dwo to remove those sections from the original .o file. 🧚
  • --extract-dwo — extracts the contents of all DWARF .dwo sections. Peep --strip-dwo above for the full lore.
  • --file-alignment num — sets the file alignment. Sections in the file will always begin at file offsets that are multiples of this number. Defaults to 512. [This option is specific to PE targets.]
  • --heap reserve
  • --heap reserve,commit — specify the number of bytes of memory to reserve (and optionally commit) to be used as heap for this program. [This option is specific to PE targets.]
  • --image-base value — use value as the base address of your program or dll. This is the lowest memory location that gets used when your program or dll is loaded. To reduce the need to relocate and boost performance of your dlls, each one should have a unique base address and not overlap any other dlls. The default is 0x400000 for executables, and 0x10000000 for dlls. [This option is specific to PE targets.]
  • --section-alignment num — sets the section alignment field in the PE header. Sections in memory will always begin at addresses which are a multiple of this number. Defaults to 0x1000. [This option is specific to PE targets.]
  • --stack reserve
  • --stack reserve,commit — specify the number of bytes of memory to reserve (and optionally commit) to be used as stack for this program. [This option is specific to PE targets.]
  • --subsystem which
  • --subsystem which:major
  • --subsystem which:major.minor — specifies the subsystem under which your program will execute. The legal values for which are native, windows, console, posix, efi-app, efi-bsd, efi-rtd, sal-rtd, and xbox. You may optionally set the subsystem version too. Numeric values are also accepted for which. [This option is specific to PE targets.]
  • --extract-symbol — keeps the file's section flags and symbols but removes all section data. Specifically, the option:
    • removes the contents of all sections;
    • sets the size of every section to zero; and
    • sets the file's start address to zero.

This option is used to build a .sym file for a VxWorks kernel. It can also be a genuinely useful way of shrinking a --just-symbols linker input file. 🌸

  • --compress-debug-sections — compresses DWARF debug sections using zlib with SHF_COMPRESSED from the ELF ABI. Note: if compression would actually make a section larger, then it is not compressed. no bloating allowed 💀
  • --compress-debug-sections=none
  • --compress-debug-sections=zlib
  • --compress-debug-sections=zlib-gnu
  • --compress-debug-sections=zlib-gabi
  • --compress-debug-sections=zstd — for ELF files, these control how DWARF debug sections get compressed. --compress-debug-sections=none is equivalent to --decompress-debug-sections. --compress-debug-sections=zlib and --compress-debug-sections=zlib-gabi are equivalent to --compress-debug-sections. --compress-debug-sections=zlib-gnu compresses DWARF debug sections using the obsoleted zlib-gnu format — the debug sections get renamed to begin with .zdebug. --compress-debug-sections=zstd compresses DWARF debug sections using zstd. Note: if compression would actually make a section larger, then it is not compressed nor renamed. 🎀
  • --decompress-debug-sections — decompresses DWARF debug sections. For a .zdebug section, the original name is restored. lowkey the undo button 🦋
  • --elf-stt-common=yes
  • --elf-stt-common=no — for ELF files, these control whether common symbols should be converted to the STT_COMMON or STT_OBJECT type. --elf-stt-common=yes converts common symbol type to STT_COMMON. --elf-stt-common=no converts common symbol type to STT_OBJECT.
  • --merge-notes
  • --no-merge-notes — for ELF files, attempt (or do not attempt) to reduce the size of any SHT_NOTE type sections by removing duplicate notes. dedupe slay ✨
  • -V
  • --version — shows the version number of objcopy.
  • --verilog-data-width=bytes — for Verilog output, this controls the number of bytes converted for each output data element. The input target controls the endianness of the conversion.
  • -v
  • --verbose — verbose output: lists all object files modified. In the case of archives, objcopy -V lists all members of the archive. 👀
  • --help — shows a summary of the options to objcopy.
  • --info — displays a list showing all architectures and object formats available.
  • @file — reads command-line options from file. The options read get inserted in place of the original @file option. If file doesn't exist, or can't be read, then the option is treated literally, and not removed. 🫶

Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively. it's giving inception, fr fr 💫

🌈 SEE ALSO 🌈

ld(1), objdump(1), and the Info entries for binutils.

Copyright (c) 1991-2023 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

and that's the whole page bestie, we did it 💅✨ this was binutils-2.40.50, dated 2023-07-04, filed under OBJCOPY(1). go forth and copy those objects, you ate 🫶👑

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