OBJCOPY(1)

📦
version 2.45.50.20251209+3.5.3build1 · 5 versions
, in ubuntu resolute, ubuntu stonking

💖 NAME 💖

okay so bestie, meet objcopy — she's a GNU Development Tools girlie, and yes, this is her OBJCOPY(1) manual page. Her whole entire job? copy and translate object files. That's it. That's the girl. ✨

🎀 SYNOPSIS 🎀

like, here's the whole vibe of how you'd actually call her:

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]
        [--binary-symbol-prefixstring]
        [--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=reserve[,commit]]
        [--image-base=address]
        [--section-alignment=num]
        [--stack=reserve[,commit]
        [--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]

(yes she has a LOT of flags. she's an overachiever. we love her for it. 💅)

🌸 DESCRIPTION 🌸

So the tea: the GNU objcopy utility copies the contents of one object file into another one. That's the whole plot. 🫶

objcopy uses the GNU BFD Library to read and write the object files, which is how she's able to write the destination object file in a format that's completely different from the source file's format. What exactly she does is controlled by the command-line options you hand her. And ngl, there's a caveat here:

Note that objcopy should be able to copy a fully linked file between any two formats. However, copying a relocatable object file between any two formats may not work as expected. 😭 so don't come for her if that one acts up.

When she's doing her translations, objcopy creates temporary files and then deletes them afterward. She does all the translation work with BFD, which means she has access to every single format described in BFD, so she can recognize most formats without you having to tell her what they are. She just knows. main character energy honestly. ✨

You can also use objcopy to generate S-records by setting the output target to srec (like, do -O srec).

And you can use objcopy to generate a raw binary file by setting the output target to binary (like, do -O binary). When she generates a raw binary file, she basically produces a memory dump of the contents of the input object file. Heads up though:

  • All symbols and relocation information will be discarded. gone. poof. 💀
  • The memory dump will start at the load address of the lowest section that got copied into the output file.

When you're generating an S-record or a raw binary file, it may be helpful to use -S to remove sections that contain debugging information. And in some cases -R will be useful for removing sections that contain information the binary file just doesn't need. 🧚

Note — and this is important bestie: objcopy is not able to change the endianness of its input files. If the input format has an endianness (some formats don't), objcopy can only copy the inputs into file formats that have the same endianness or that have no endianness at all (e.g., srec). (However, see the --reverse-bytes option. 👀)

✨ OPTIONS ✨

okay this is the long part, buckle up, we're going option by option and I'm not skipping a single one. 💖

  • infile, outfile — the input and output files, respectively. If you don't specify outfile, objcopy creates a temporary file and then destructively renames the result using the name of infile. so like, she will overwrite your input file. be aware. 😭
  • -I bfdname, --input-target=bfdname — treat the source file's object format as bfdname instead of trying to figure it out herself.
  • -O bfdname, --output-target=bfdname — write the output file using the object format bfdname.
  • -F bfdname, --target=bfdname — use bfdname as the object format for both the input and the output file; i.e., just transfer the data from source to destination with no translation at all. lazy girl behavior and honestly, valid. 💅
  • -B bfdarch, --binary-architecture=bfdarch — this one's useful when you're transforming an architecture-less input file into an object file. In that case the output architecture can be set to bfdarch. This option gets ignored if the input file already has a known bfdarch. You can access this binary data inside a program by referencing the special symbols created by the conversion process, which 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. 📸
  • -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 an 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.

  • -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. do not do this. 🙈

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.

  • --keep-section=sectionpattern — when removing sections from the output file, keep the sections that match sectionpattern. 🫶
  • --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.*.

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.

  • --strip-section-headers — strip the section headers. This option is specific to ELF files. It implies --strip-all and --merge-notes. 🔥
  • -S, --strip-all — do not copy relocation and symbol information from the source file. Also deletes debug sections. she's taking it ALL off. 💅
  • -g, --strip-debug — do not copy debugging symbols or sections from the source file.
  • --strip-unneeded — remove all symbols that are not needed for relocation processing, in addition to the debugging symbols and sections already stripped by --strip-debug.
  • -K symbolname, --keep-symbol=symbolname — when stripping symbols, keep the symbol symbolname even if it would normally get stripped. This option may be given more than once. 🥺
  • -N symbolname, --strip-symbol=symbolname — do not copy the symbol symbolname from the source file. This option may be given more than once.
  • --strip-unneeded-symbol=symbolname — do not copy the symbol symbolname from the source file unless it is needed by a relocation. This option may be given more than once.

okay and that's just part one bestie, there's SO much more coming, stay with me 💜

  • -G symbolname, --keep-global-symbol=symbolname — bestie, this one keeps only symbolname global 💅 and makes every other symbol local to the file so they are not visible externally. You can drop this option more than once. Note: this option cannot be used in conjunction with the --globalize-symbol or --globalize-symbols options. Periodt.
  • --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. Slay.
  • -L symbolname, --localize-symbol=symbolname — convert a global or weak symbol called symbolname into a local symbol, so that it is not visible externally. This option may be given more than once. Note - unique symbols are not converted. Lowkey important.
  • -W symbolname, --weaken-symbol=symbolname — make symbol symbolname weak. This option may be given more than once. Iconic.
  • --binary-symbol-prefix=string — when used with --input-target=binary, sets string as the base name for the symbols generated for the input file. These symbols are:
<string>_start
<string>_end
<string>_size

By default, the binary input handler derives the prefix symbol name from a mangled version of the input file name and _binary prefix. This option allows specifying it explicitly. Obsessed.

  • --globalize-symbol=symbolname — give symbol symbolname global scoping so that it is 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. No cap.
  • -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". The way that works? Chef's kiss.

  • -x, --discard-all — do not copy non-global symbols from the source file. Bye.
  • -X, --discard-locals — do not copy compiler-generated local symbols. (These usually start with L or ..) 👀
  • -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 fashion.
  • -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. So specific.
  • --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. That is actually so cool.
  • -p, --preserve-dates — set the access and modification dates of the output file to be the same as those of the input file. This option also copies the date stored in a PE format file's header, unless the SOURCE_DATE_EPOCH environment variable is defined. If it is defined then this variable will be used as the date stored in the header, interpreted as the number of seconds since the Unix epoch. Time travel but make it Unix.
  • -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. Deterministic queen.
  • -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. No filter.
  • --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. Patience.
  • --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. Fill her up.
  • --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). Pad it out.
  • --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. Main character entry.
  • --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.
  • --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. > ⚠️ Dangerous if you do not know what you are doing.
  • --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 realness.
  • --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. LMA lore.
  • --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. > ⚠️ Note - changing the VMA of sections in a fully linked binary can be dangerous since there may be code that expects the sections to be located at their old address. Be careful bestie.
  • --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 queen.
  • --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. Silent mode.
  • --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, debug, and large. 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. The ELF x86-64 specific flag large corresponds to SHF_X86_64_LARGE. Flags for days.
  • --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.... Alignment is key.

okay so real quick before we move on — setting a section's alignment will not magically align its LMA or VMA addresses too, they're separate things bestie 😭. If those actually need changing, that's what --change-section-lma and/or --change-section-vma are for. And also — heads up — changing VMAs can cause problems in fully linked binaries, because there may be code in there that just expects the contents of the sections to be sitting at their old address. it will simply not vibe with the new address 💀.

  • --add-section sectionname=filename — adds a brand new section called sectionname while it's copying the file 🎀. The contents of this new section come straight from the file filename, and the size of the section will be the size of that file. tiny detail, huge deal: this only works on file formats that can actually support sections with arbitrary names. Also, you may need to reach for --set-section-flags to set the attributes of the freshly created section, otherwise it's just kinda standing there with no flags 🙈.
  • --dump-section sectionname=filename — takes the contents of the section named sectionname and drops them into the file filename, overwriting whatever was already chilling in there. This is the inverse of --add-section. It's also similar to --only-section, except it doesn't create a formatted file — it just dumps the contents as raw binary data, with zero relocations applied. raw. unfiltered. no makeup. You can specify this option more than once ✨.
  • --update-section sectionname=filename — swaps out the existing contents of the section named sectionname with the contents of the file filename. The section's size gets adjusted to the size of the file. The section flags for sectionname stay unchanged 🫶. And for ELF format files, the section-to-segment mapping also remains unchanged — which is something you literally cannot pull off with --remove-section followed by --add-section. You can specify this option more than once.
note — you can use --rename-section and --update-section together to both update and rename a section from one command line, iconic behavior honestly 👑. In that case: pass the original section name to --update-section, and pass both the original and new section names to --rename-section.
  • --add-symbol name=[section:]value[,flags] — adds a new symbol called name while copying the file. May be specified multiple times 💅. If the section is given, the symbol gets associated with that section and is relative to it — otherwise it's an ABS symbol. Specifying an undefined section will result in a fatal error 😭. There is no check for the value; it will be taken as specified, no questions asked. Symbol flags can be specified, but not all flags will be meaningful for all object file formats. By default, the symbol will be global. And the special flag before=othersym will insert the new symbol in front of the specified othersym — otherwise the symbol(s) get added at the end of the symbol table in the order they appear ✨.
  • --rename-section oldname=newname[,flags] — renames a section from oldname to newname, optionally changing the section's flags to flags while it's at it. The advantage over using a linker script to do the rename is that the output stays as an object file and does not become a linked executable 🌸. This option accepts the same set of flags as --set-section-flags.

This one is particularly helpful when the input format is binary, because binary input will always create a section called .data 🙈. So if, for example, you wanted to instead create a section called .rodata containing binary data, you could use the following command line to achieve it:

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} — controls the handling of long section names when processing "COFF" and "PE-COFF" object formats. The default behaviour, keep, is to preserve long section names if any are present in the input file. The enable and disable options forcibly enable or disable the use of long section names in the output object; when disable is in effect, any long section names in the input object will be truncated. The enable option will only emit long section names if any are present in the inputs — mostly the same as keep, but it's left undefined whether enable might force the creation of an empty string table in the output file 🤷 (mysterious. we love that for it).
  • --change-leading-char — some object file formats use special characters at the start of symbols. The most common such character is underscore, which compilers often add before every symbol. This option tells objcopy to change the leading character of every symbol when it converts between object file formats ✨. If the object file formats use the same leading character, this option has no effect. Otherwise, it will 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 the character. The most common symbol leading character is underscore, so this option will remove a leading underscore from all global symbols 🎀. This can be useful if you want to link together objects of different file formats with different conventions for symbol names. It's different from --change-leading-char because it always changes the symbol name when appropriate, regardless of the object file format of the output file.
  • --reverse-bytes=num — reverses the bytes in a section with output contents. A section's length must be evenly divisible by the value given in order for the swap to be able to take place 🫶. And reversing takes place before the interleaving is performed.

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 are 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 ✨.
  • --srec-forceS3 — meaningful only for srec output. Avoids generation of S1/S2 records, creating S3-only record format 💅.
  • --redefine-sym old=new — changes the name of a symbol old, to new. This can be useful when you're trying to link two things together for which you have no source, and there are name collisions 😭 the classic "we don't have the source and everything is called the same thing" situation.
  • --redefine-syms=filename — applies --redefine-sym to each symbol pair "old new" listed in the file filename. filename is simply a flat file, with one symbol pair per line 🎀. Line comments may be introduced by the hash character. This option may be given more than once.
  • --weaken — changes all global symbols in the file to be weak. This can be useful when building an object which will be linked against other objects using the -R option to the linker. This option is only effective when using an object file format which supports weak symbols ✨.
  • --keep-symbols=filename — applies --keep-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character 🫶. This option may be given more than once.
  • --strip-symbols=filename — applies --strip-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once ✨.
  • --strip-unneeded-symbols=filename — applies --strip-unneeded-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once 🌸.
  • --keep-global-symbols=filename — applies --keep-global-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once 💅.
  • --localize-symbols=filename — applies --localize-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once 🎀.
  • --globalize-symbols=filename — applies --globalize-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option may be given more than once. Note: this option cannot be used in conjunction with the -G or --keep-global-symbol options — pick a lane bestie 😭.
  • --weaken-symbols=filename — applies --weaken-symbol to each symbol listed in the file filename. filename is simply a flat file, with one symbol name per line. Line comments may be introduced by the hash character. This option 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 👑. This is useful in case a machine is assigned an official code and the tool-chain adopts the new code, but other applications still depend on the original code being used. 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 🌈.
  • --writable-text — marks the output text as writable. This option isn't meaningful for all object file formats 🤷.
  • --readonly-text — makes the output text write protected. This option isn't meaningful for all object file formats 💅.
  • --pure — marks your output file as demand paged 🫶. Okay but real talk: this option isn't meaningful for all object file formats, so don't come for it if it does nothing on yours.
  • --impure — marks your output file as impure 😈. Same lil disclaimer: not meaningful for all object file formats.
  • --prefix-symbols=string — glues string onto the front of every single symbol in the output file. All of them. No cap. ✨
  • --prefix-sections=string — same energy but for section names: every section name in the output file gets string slapped on the front 🎀
  • --prefix-alloc-sections=string — and this one prefixes the names of all the allocated sections in the output file with string. Just the allocated ones, bestie, we're being specific 💅
  • --add-gnu-debuglink=path-to-file — creates a .gnu_debuglink section that references path-to-file and drops it into the output file 🔗. Lowkey important: the file at path-to-file must exist. Part of adding this section is embedding a checksum of the contents of the debug info file into the section, so yeah, it needs the actual file.

Now listen, this is the part people trip on 🙈: if the debug info file is built in one location but it's getting installed somewhere else later, do not use the path to the installed location. The --add-gnu-debuglink option will fail, because the installed file doesn't exist yet. Instead, put the debug info file in the current directory and use --add-gnu-debuglink with no directory components at all, like this:

objcopy --add-gnu-debuglink=foo.debug

At debug time, the debugger goes looking for the separate debug info file in a bunch of known locations. The exact set varies by distribution, but it typically includes:

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

As long as the debug info file has been installed into one of those spots before the debugger runs, everything should work correctly 🌈

  • --keep-section-symbols — when you're stripping a file (maybe with --strip-debug or --strip-unneeded), this keeps any symbols that specify section names — the ones that would otherwise get stripped away 🛟
  • --keep-file-symbols — same deal, but for symbols specifying source file names. Those would otherwise get stripped; this keeps them safe 💖
  • --only-keep-debug — strips a file by removing the contents of any sections that --strip-debug would not strip, and leaves the debugging sections intact. In ELF files, this preserves all note sections in the output 👑

Note: the section headers of the stripped sections are preserved — including their sizes — but the contents of the section are 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 different address space. Iconic behaviour honestly.

The intention is that this option gets used together with --add-gnu-debuglink to create a two-part executable 🫶: one stripped binary that takes up less space in RAM and in a distribution, and a second debugging information file that's only needed if you actually want to debug. The suggested procedure to create these files goes like this:

  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 for the debug info file is arbitrary, fr fr. Also the --only-keep-debug step is optional. 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. Besides, 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. So don't try it 💀
  • --strip-dwo — removes the contents of all DWARF .dwo sections, leaving the remaining debugging sections and all symbols intact 🧚. This one's intended for the compiler to use 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 to the .dwo file, then --strip-dwo to remove those sections from the original .o file. Clean up after yourself, periodt 💅
  • --extract-dwo — extracts the contents of all DWARF .dwo sections. Peep the --strip-dwo option above for the full lore 👀
  • --file-alignment num — specifies 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 and --heap reserve,commit — specifies 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 — uses 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 improve performance of your dlls, each one should have a unique base address and not overlap any other dlls — main character energy only, no overlap bestie. The default is 0x400000 for executables, and 0x10000000 for dlls. [This option is specific to PE targets.]
  • --section-alignment num — [This option is specific to PE targets.]

Sets the section alignment field in the PE header — if one is present in the binary. Sections in memory will always begin at addresses that are a multiple of this number. Defaults to 0x1000.

Note — if a section's LMA or VMA addresses are no longer aligned, and those addresses haven't been set via the --set-section-lma or --set-section-vma options, and the file has been fully relocated, then a warning message will be issued. It's then up to you to decide if the LMA and VMA need updating. Good luck with that 🙏
  • --stack reserve and --stack reserve,commit — specifies 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 useful way of reducing the size of 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. Common sense, we love to see it.
  • --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 ✨. Here's the tea:
    • --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 are 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 🌸
  • --elf-stt-common=yes and --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". Pick your fighter 👑
  • --merge-notes and --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 🩹. Duplicate notes? Not on our watch.
  • -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 are inserted in place of the original @file option. If file doesn't exist, or can't be read, then the option gets treated literally, and is not removed. No silent disappearing acts here.

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 🔁🦋

✨ SEE ALSO ✨

ok so if you liked this you're gonna love the whole friend group 💖

  • ld(1) — the linker bestie, brings everything together
  • objdump(1) — the one who reads the tea back to you, dissects all your objects
  • and the Info entries for binutils — like, the extended lore, iykyk 🦋

so like, legally speaking 👑

Copyright (c) 1991-2025 Free Software Foundation, Inc.

you are hereby granted permission 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". 🫶

fr fr read the license, it's giving "we trust you, just keep it free" energy and that's iconic of them

okay bestie that's a wrap on the whole page, you made it to the end 💅✨

this was binutils-2.45.50, dated 2026-01-13, and it lives under OBJCOPY(1) — go copy some objects, you absolute main character 👑🦋💖

📦 where this page comes from