OBJCOPY(1)

📦
version 26.09 · 2 versions
, in nixpkgs unstable

🎀 NAME 🎀

OBJCOPY(1) is the GNU Development Tools bestie for object files: objcopy copies and translates object files, periodt. 💅

✨ 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]
        [--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]

💖 DESCRIPTION 💖

Okay so the GNU objcopy utility is literally copying the contents of an object file into 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 is different from the source object file’s format. The exact behavior of objcopy is controlled by command-line options. 🫶

Important vibe check: 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. Not me warning you bestie, it’s just facts. 😭

objcopy 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. Iconic BFD behavior, honestly. ✨

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

You can also use objcopy 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. Memory dump energy, but make it precise. 💅

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. 🔥

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.) 🌈

🌸 OPTIONS 🌸

  • infile — the input file, bestie. The source of the whole situation. 💖
  • outfile — the output file, respectively. If you do not specify outfile, objcopy creates a temporary file and destructively renames the result with the name of infile. Destructively renames, not me being dramatic, that’s literally what it says. 😭
  • -I bfdname, --input-target=bfdname — consider the source file’s object format to be bfdname, rather than attempting to deduce it. No guessing, we’re telling it directly. ✨
  • -O bfdname, --output-target=bfdname — write the output file using the object format bfdname. Slay, specified format. 💅
  • -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. Zero translation, just vibes and bytes. 🦋
  • -B bfdarch, --binary-architecture=bfdarch — useful when transforming an 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. Picture file to object file pipeline, obsessed. 🎀
  • -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. Exclamation point said “not today.” 💀

  • -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. 🚨

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. Exclamation point is protecting that one section, lowkey iconic. ✨

  • --keep-section=sectionpattern — when removing sections from the output file, keep sections that match sectionpattern. Keep section, keep peace. 🫶
  • --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.*. Relocations removed, chaos managed (hopefully). 😭

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. Exclamation point stays winning. 💅

  • --strip-section-headers — strip section headers. This option is specific to ELF files. Implies --strip-all and --merge-notes. 🧚
  • -S, --strip-all — do not copy relocation and symbol information from the source file. Also deletes debug sections. Gone, reduced to atoms. 🔥
  • -g, --strip-debug — do not copy debugging symbols or sections from the source file. Bye debug info, love you though. 💖
  • --strip-unneeded — remove all symbols that are not needed for relocation processing in addition to debugging symbols and sections stripped by --strip-debug. Unneeded symbols? Not invited to the function. ✨
  • -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. Protected symbol, bestie privilege. 🎀
  • -N symbolname, --strip-symbol=symbolname — do not copy symbol symbolname from the source file. This option may be given more than once. Blocked. Do not copy. Periodt. 💀
  • --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. Only stays if relocation says it’s needed, otherwise it’s out. 🦋
  • -G symbolname, --keep-global-symbol=symbolname — bestie, this one says: keep only symbolname global, periodt. Every other symbol gets made local to the file so it's not visible externally. You can pass this more than once if you've got a whole squad of symbols to keep. > Heads up though: this option cannot be used together with --globalize-symbol or --globalize-symbols. They're giving sworn enemies, ngl. 💅
  • --localize-hidden — in an ELF object, this marks all symbols that have hidden or internal visibility as local. It stacks on top of the symbol-specific localization options like -L, so it's giving "layer it like your skincare routine". ✨
  • -L symbolname, --localize-symbol=symbolname — converts a global or weak symbol called symbolname into a local symbol, so it's not visible externally. May be given more than once, bestie, go off. > Note: unique symbols are not converted. 🙈
  • -W symbolname, --weaken-symbol=symbolname — makes symbol symbolname weak. This option may be given more than once. Lowkey the easiest glow-down ever. 🫶
  • --binary-symbol-prefix=string — when you use it with --input-target=binary, it sets string as the base name for the symbols generated for the input file. Those 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 plus the _binary prefix. This option just lets you specify it explicitly, which is so much cleaner. 🎀

  • --globalize-symbol=symbolname — gives symbol symbolname global scoping so it's visible outside of the file it's defined in. May be given more than once. > Note: this option cannot be used in conjunction with -G or --keep-global-symbol. Same beef as before, fr fr. 😭
  • -w, --wildcard — permits regular expressions in symbol names used in other command line options. The question mark (?), asterisk (*), backslash (\) and square brackets ([]) operators can be used anywhere in the symbol name. And here's the iconic twist: 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 ! really said "not you, girl". 💀

  • -x, --discard-all — do not copy non-global symbols from the source file. We're decluttering, main character energy only. 🧚
  • -X, --discard-locals — do not copy compiler-generated local symbols. (These usually start with L or ..) Bye, you won't be missed. 👋
  • -b byte, --byte=byte — if interleaving has been enabled via the --interleave option, then start the range of bytes to keep at the *byte*th byte. byte can be in the range from 0 to breadth-1, where breadth is the value given by the --interleave option. Math queen behavior. 👑
  • -i [breadth], --interleave[=breadth] — only copy a range out of every breadth bytes. (Header data is not affected, so don't worry about that.) You select which byte in the range begins the copy with the --byte option, and you select the width of the range with the --interleave-width option.

This option is useful for creating files to program ROM, which is honestly such a vibe. It's typically used with an "srec" output target. > Note that objcopy will complain if you do not specify the --byte option as well. It's not being mean, it just needs both.

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. Slay, quarter of the data. 🌸

  • --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. Teamwork makes the dream work, fr fr.

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. Literally splitting the digits like a friendship bracelet. 🎀

  • -p, --preserve-dates — set the access and modification dates of the output file to be the same as those of the input file. Copying the vibe and the timestamps, obsessed.

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. ⭐

  • -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. Everything uniform, everything cute, everything reproducible. ✨

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

  • -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. Keep the original lore. 💜

This is the default unless binutils was configured with --enable-deterministic-archives.

  • --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. So it's giving "yes queen but she takes a minute". 😭
  • --gap-fill val — fill gaps between sections with val. This operation applies to the load address (LMA) of the sections. It's done by increasing the size of the section with the lower address, and filling in the extra space created with val. Filling the void with ✨content✨.
  • --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).
  • --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, so no cap — some formats just aren't built for that. 🙈
  • --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. Same caveat, same girl. 🫶
  • --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're loaded at a different address, the program may fail. Like moving someone's furniture while they sleep, careful please. 💀
  • --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. ⚠️
  • --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. 🦋
  • --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. Do not do this casually, bestie, I'm serious. 🔥
  • --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, so it's already on unless you say otherwise. 🎀
  • --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, I guess. 🤫
  • --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 are basically the section's personality traits. 🌈
  • --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.... No in-between numbers, she's picky like that. ⭐
🌸 ok bestie, quick lil heads-up before we keep rolling: setting a section's alignment does not automagically align its LMA or VMA addresses. like, at all. if those need changing too, you gotta reach for --change-section-lma and/or --change-section-vma. also ⚠️ changing VMAs can cause problems in fully linked binaries, because there may be code out there that expects the contents of the sections to live at their old address. it's giving "she moved and didn't leave a forwarding address" 😭
  • --add-section sectionname=filename — adds a brand new section named sectionname while copying the file 💖 the contents of the new section come straight from the file filename, and the section's size is literally the size of that file. heads up though: this only works on file formats that can support sections with arbitrary names. and ngl, you may need to use --set-section-flags to set the attributes of your newly created section, otherwise she's just sitting there with default vibes ✨
  • --dump-section sectionname=filename — takes the contents of the section named sectionname and drops them into the file filename, overwriting whatever was chilling there before (sorry to that file 🙈). this is the exact inverse of --add-section. it's similar to the --only-section option, except it doesn't create a formatted file — it just dumps the contents as raw binary data, and no relocations get applied. can be specified more than once, queen 💅
  • --update-section sectionname=filename — swaps out the existing contents of a section named sectionname with the contents of the file filename. the section's size gets adjusted to match the file's size, and the section flags for sectionname stay completely unchanged. for ELF format files, the section-to-segment mapping also stays unchanged — which is a thing that is genuinely not possible if you go the --remove-section then --add-section route 🫶. can be specified more than once.
🎀 note: you can use --rename-section and --update-section together on one command line to both update and rename a section. in that case, pass the original section name to --update-section, and pass both the original and the new section names to --rename-section. iykyk.
  • --add-symbol name=[section:]value[,flags] — adds a new symbol named name while copying the file. may be specified multiple times 🔥 if you give a section, the symbol gets associated with and relative to that section — otherwise it's an ABS symbol. specifying an undefined section = fatal error, no cap 💀. there is no check for the value, it just gets taken exactly as you specified it. symbol flags can be specified, but not all flags are meaningful for all object file formats. by default the symbol will be global. 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 in the process. the glow-up here vs. using a linker script to do the rename: the output stays as an object file and doesn't become a linked executable 💅 this option accepts the same set of flags as the --set-section-flags option.

it's especially helpful when the input format is binary, since that will always create a section called .data. so like, say you wanted a section called .rodata holding your binary data instead — you'd run:

objcopy -I binary -O <output_format> -B <architecture> \
 --rename-section .data=.rodata,alloc,load,readonly,data,contents \
 <input_binary_file> <output_object_file>

and boom, she's renamed ✨

  • --long-section-names {enable,disable,keep} — controls how long section names get handled 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. enable and disable 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 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's left undefined whether enable might force the creation of an empty string table in the output file. so, like, unspecified behavior, bestie 🫠
  • --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'll add a character, 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 remove a leading underscore from all global symbols 🎀 this can be useful if you wanna link together objects of different file formats with different conventions for symbol names. and 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 👑
  • --reverse-bytes=num — reverses the bytes in a section with output contents 🔥 the section length must be evenly divisible by the value you give in order for the swap to be able to take place — no leftovers, periodt. reversing takes place before the interleaving is performed.

this option is typically used in 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 🌸

and 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 🦋 (yes, it stacks, she's multi-talented)

  • --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. useful when you're trying to link two things together for which you have no source, and there are name collisions 😤
  • --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 🫶 useful when building an object that'll 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, jsyk 💜
  • --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 ⚠️
  • --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 🔥 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. for ELF based architectures, if the index alternative doesn't 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, jsyk.
  • --readonly-text — makes the output text write protected 🛡️ this option isn't meaningful for all object file formats either.
  • --pure — marks the output file as demand paged 💅. This one isn’t meaningful for every object file format, bestie — it’s giving “depends on the target”.
  • --impure — marks the output file as impure 🫶. Again, not meaningful for all object file formats.
  • --prefix-symbols=string — puts string in front of every symbol in the output file. Little name tag era ✨.
  • --prefix-sections=string — puts string in front of every section name in the output file. Section names getting the group-chat prefix treatment 🎀.
  • --prefix-alloc-sections=string — puts string in front of all the names of all allocated sections in the output file. Yes, allocated sections only — read the assignment, babe 📚.
  • --add-gnu-debuglink=path-to-file — creates a .gnu_debuglink section that contains a reference to path-to-file, then adds it to the output file. Big important note: the file at path-to-file must exist 😭. Part of adding the .gnu_debuglink section involves embedding a checksum of the contents of the debug info file into the section.

If the debug info file is built in one location but is going to be installed later into a different location, 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 will attempt to look for the separate debug info file in a set of known locations. The exact set of these locations varies depending upon the distribution being used, 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 these locations before the debugger is run, everything should work correctly 💖.

  • --keep-section-symbols — when stripping a file, perhaps with --strip-debug or --strip-unneeded, retain any symbols specifying section names, which would otherwise get stripped. Protecting the section-name besties from getting deleted 🛡️.
  • --keep-file-symbols — when stripping a file, perhaps with --strip-debug or --strip-unneeded, retain any symbols specifying source file names, which would otherwise get stripped. Source file symbols stay in the chat ✨.
  • --only-keep-debug — strips a file by removing contents of any sections that would not be stripped by --strip-debug, 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. The section headers are preserved so that other tools can match up the debuginfo file with the real executable, even if that executable has been relocated to a different address space. Literally matchmaking debug info with the real binary 💘.

The intention is that this option will be used in conjunction with --add-gnu-debuglink to create a two part executable. One is a stripped binary which will occupy less space in RAM and in a distribution; the second is a debugging information file which is only needed if debugging abilities are required. The suggested procedure to create these files is as follows:

  1. Link the executable as normal. Assuming that it is 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. 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 the --add-gnu-debuglink can be the full executable. It does not have to be a file created by the --only-keep-debug switch. Not me expecting you to remember that — but bestie, remember that 😌.

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 no chaotic multi-debug-file situations, okay? 💀

  • --strip-dwo — removes the contents of all DWARF .dwo sections, leaving the remaining debugging sections and all symbols intact. This option is intended for use by the compiler as part of the -gsplit-dwarf option, which splits debug information between the .o file and a separate .dwo file. The compiler generates all debug information in the same file, then uses the --extract-dwo option to copy the .dwo sections to the .dwo file, then the --strip-dwo option to remove those sections from the original .o file. Split-debug-info slay 🦋.
  • --extract-dwo — extracts the contents of all DWARF .dwo sections. See the --strip-dwo option for more information. Copy-paste the debug bits, but make it Unix 🌸.
  • --file-alignment num — specify the file alignment. Sections in the file will always begin at file offsets which are multiples of this number. This defaults to 512. [This option is specific to PE targets.] Alignment girlies rise 🎀.
  • --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.] Heap space: reserved, committed, iconic 💅.
  • --image-base value — use value as the base address of your program or dll. This is the lowest memory location that will be used when your program or dll is loaded. To reduce the need to relocate and improve performance of your dlls, each 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.] Lowest address behavior, but make it cute ✨.
  • --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 which 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 have not 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 will then be up to the user to decide if the LMA and VMA need updating. Warning era, but make it your problem now 😭.

  • --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.] Stack space gets the reserve-and-commit treatment 🔥.
  • --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 also. Numeric values are also accepted for which. [This option is specific to PE targets.] Choose your fighter, bestie 👑.
  • --extract-symbol — keep the file’s section flags and symbols but remove all section data. Specifically, this option:
    • Removes the contents of all sections.
    • Sets the size of every section to zero.
    • 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. Symbols stay, section data leaves — it’s giving minimalist 💅.

  • --compress-debug-sections — compress 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 glow-up if it makes things worse, periodt 🫶.
  • --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 options control how DWARF debug sections are 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 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. The vibe check says no 💀.

  • --decompress-debug-sections — decompress DWARF debug sections. For a .zdebug section, the original name is restored. Un-shrink, un-rename, restore the original name — self-care 😌.
  • --elf-stt-common=yes, --elf-stt-common=no — for ELF files, these options 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. Symbol type glow-up, choose wisely ✨.
  • --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. Deduplicate the notes or don’t — consent is key 🫶.
  • -V, --version — show the version number of objcopy. Version reveal, but make it utility 🔥.
  • --verilog-data-width=bytes — for Verilog output, this options controls the number of bytes converted for each output data element. The input target controls the endianness of the conversion. Verilog data width, but keep the endianness honest 🌈.
  • -v, --verbose — verbose output: list all object files modified. In the case of archives, objcopy -V lists all members of the archive. Yes, that says objcopy -V — we’re just reading the manual, bestie 😭.
  • --help — show a summary of the options to objcopy. Help me help you 🎀.
  • --info — display a list showing all architectures and object formats available. The whole menu of architectures and formats, no cap 👑
  • @file — read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be 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. Recursive group-chat option energy, iykyk 💜.

💫 SEE ALSO 💫

okay so when you're done vibing with objcopy, here's your little bestie squad to keep the party going:

  • ld(1) — the linker, the one who actually puts all your stuff together 🧩
  • objdump(1) — the nosy one who reads everything back to you, iconic duo behavior honestly 💅
  • the Info entries for binutils — literally the whole lore, deep dive material, iykyk 📚✨

hotpink Copyright (c) 1991-2026 Free Software Foundation, Inc. — yup, they've been at this since before some of us were even born, no cap 👑

so here's the whole situation bestie, and it's actually really sweet: 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. 🫶

and a copy of the license is included in the section entitled "GNU Free Documentation License" — so if you wanna read the whole thing, it's right there waiting for you 🌸

fr fr, that's the actual legal vibe — go forth and share, just keep the terms intact, periodt ✨

okay bye bestie, go forth and copy those objects 🦋🔥

this lil doc dropped as part of binutils-2.46.1, dated 1980-01-01 (yes the date is a whole joke, the manpage said it not me 💀) — mwah, love u, see u in the group chat 💖

📦 where this page comes from