OBJCOPY(1)

📦
version 2.45.50.20251209 · 5 versions
, in ubuntu resolute, ubuntu stonking

OBJCOPY(1) — GNU Development Tools ✨

okay bestie, welcome to the objcopy manual, but make it cute 💅. We are keeping every flag, every warning, every little detail. No cap.

🌸 NAME 🌸

objcopy — copy and translate object files 🦋

🎀 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 the copy-paste queen of object files 👑. It copies the contents of an object file to another. objcopy uses the GNU BFD Library to read and write the object files. It can write the destination object file in a format different from that of the source object file. The exact behavior of objcopy is controlled by command-line options. 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 😭.

objcopy creates temporary files to do its translations and deletes them afterward. objcopy 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.

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

objcopy can be used 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. 💾

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.
  • outfile — the output file. The input and output files are respectively infile and outfile. If you do not specify outfile, objcopy creates a temporary file and destructively renames the result with the name of infile. 🫶
  • -I bfdname, --input-target=bfdname — consider the source file's object format to be bfdname, rather than attempting to deduce it. 🔍
  • -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., simply transfer data from source to destination with no translation. ✨
  • -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. 🖼️
  • -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 sectinos 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. 🚨

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 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 section header. 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. 🔥
  • -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 debugging symbols and sections stripped by --strip-debug. 🧹
  • -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. 🥺
  • -N symbolname, --strip-symbol=symbolname — do not copy symbol symbolname from the source file. This option may be given more than once. ✂️
  • --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. 🫶
  • -G symbolname, --keep-global-symbol=symbolname — Okay so keep only the symbol symbolname global, bestie. Everything else gets made local to the file so it's not visible externally. You can drop this option more than once if you're feeling extra. > 🚫 But ngl, this one literally cannot be used with the --globalize-symbol or --globalize-symbols options. Periodt.
  • --localize-hidden — In an ELF object, this marks all symbols that have hidden or internal visibility as local. It stacks on top of symbol-specific localization options like -L. It's giving layered.
  • -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. Slay.
  • --binary-symbol-prefix=string — When you use it with --input-target=binary, this 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 and _binary prefix. This option lets you specify it explicitly. Iconic.

  • --globalize-symbol=symbolname — Give symbol symbolname global scoping so it's visible outside the file where it's defined. You can give this 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". Obsessed with this.

  • -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 ..) Clean.
  • -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. Bestie that's literally the default.

  • --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. Cute.

  • -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 vibes.

  • -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. Consistent 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. Fr fr.

  • --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. It's giving 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. Gap filler.
  • --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. Sad for them.
  • --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 energy.
  • --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're not careful, bestie.
  • --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-y.
  • --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. ROM girlies know.
  • --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. ⚠️ Red flag.
  • --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 but deadly.
  • --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.... Power of two only, bestie.
Quick heads-up bestie 💛 — setting a section's alignment does NOT auto-magically line up its LMA or VMA addresses. Those are a whole separate thing. If you need those moved too, you gotta reach for --change-section-lma and/or --change-section-vma. And also?? changing VMAs can cause problems in fully linked binaries, because there might be code in there that expects the contents of the sections to live at their old address. So like… be careful, okay? 😭
  • --add-section sectionname=filename — adds a brand new section called sectionname while it's copying the file 🎀. The contents of the new section come straight from the file filename, and the size of the section = the size of the file. This only works on file formats that can actually support sections with arbitrary names, so no cap, check your format first. Also note — you may need to use --set-section-flags to set the attributes of the freshly created section, otherwise it's just kinda… sitting there with no vibes.
  • --dump-section sectionname=filename — takes the contents of the section named sectionname and drops them into the file filename, overwriting whatever was in there before (sorry to that file 🙈). This is literally the inverse of --add-section. It's similar to --only-section except it does not create a formatted file — it just dumps the contents as raw binary data, no relocations applied, none of that. You can specify this option more than once, slay. 💅
  • --update-section sectionname=filename — swaps out the existing contents of a section named sectionname with the contents of file filename. The section size gets adjusted to match the size of the file. The section flags for sectionname stay unchanged. For ELF format files, the section-to-segment mapping also stays unchanged — which is a thing you literally cannot do with --remove-section followed by --add-section, so this is the moment. ✨ You can specify this option more than once.
PSA: you can use --rename-section and --update-section together to both update and rename a section from one single command line. When you do that: pass the original section name to --update-section, and pass the original and new section names to --rename-section. Iykyk. 🫶
  • --add-symbol name=[section:]value[,flags] — adds a new symbol named name while copying the file. This option may be specified multiple times. If the section is given, the symbol gets associated with and is relative to that section — otherwise it's an ABS symbol. Specifying an undefined section = fatal error, do not do it bestie. There is no check for the value, it will be taken exactly as specified. Symbol flags can be specified, and not all flags will be meaningful for all object file formats (so don't come crying to me if a flag does nothing for your format 💀). 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 in the process. The glow-up here 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 the --set-section-flags option.

This one is especially iconic when your input format is binary, because that will always create a section called .data. So say you wanted to create a section called .rodata containing binary data instead — 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 how long section names are handled when 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 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 (rip to the rest of the name ✂️). 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. Spooky. 🌸
  • --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 (it's giving nothing, honestly). 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. Super useful if you wanna link together objects of different file formats with different conventions for symbol names. 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. Periodt. 💅
  • --reverse-bytes=num — reverses the bytes in a section with output contents. A section length must be evenly divisible by the value given in order for the swap to be able to take place. Reversing takes place **before the interleaving is performed. 🔥

This option is used typically in generating ROM images for problematic target systems. Like, 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. Math is mathing. ✨

  • *--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. All of them. 🎀
  • --srec-forceS3 — meaningful only for srec output. Avoids generation of S1/S2 records, creating S3-only record format. S3 or nothing bestie. 💅
  • --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. Classic situation, honestly. 😭
  • *--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. No support, no effect, no notes. 🦋
  • *--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.
Important: 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 index-th code instead of the default one. This is 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. (Old apps stay winning, lowkey.) 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, so vibe check your format first. ✍️
  • --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 🫧 heads up bestie, this one literally does nothing on some object file formats, it's not meaningful for all of them.
  • --impure — marks the output file as impure 😌 same deal: not meaningful for every object file format out there.
  • --prefix-symbols= string — slaps string onto the front of every single symbol in the output file ✨
  • --prefix-sections= string — same energy but for section names: every section in the output file gets string glued to the front 🎀
  • --prefix-alloc-sections= string — and this one is the picky cousin: it only prefixes the names of the allocated sections with string 💜
  • --add-gnu-debuglink= path-to-file — makes a .gnu_debuglink section that points at path-to-file, then drops it into the output file 🔗
real talk: the file at path-to-file must exist. no file, no vibes. part of building that .gnu_debuglink section means embedding a checksum of the debug info file's contents right into the section.

ok so here's the trap 🪤 if the debug info file gets built in one place but installed somewhere else later, do not use the path to the installed location. --add-gnu-debuglink will fail because that installed file doesn't exist yet. instead, put the debug info file in the current directory and call the option with no directory components at all, like this:

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

at debug time the debugger goes hunting for the separate debug info file in a known set of locations. the exact set depends on your 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 is 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 yeeted.
  • --keep-file-symbols — same situation (stripping, maybe with --strip-debug or --strip-unneeded) but this one retains the symbols specifying source file names, which would otherwise get stripped too 🥺
  • --only-keep-debug — strips a file by removing the contents of any sections that --strip-debug wouldn't 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, sizes and all, but the contents get discarded. why keep the headers? so other tools can match the debuginfo file up with the real executable, even if that executable has been relocated to a different address space. iconic behaviour honestly.

the whole intention here is that you use this alongside --add-gnu-debuglink to build 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 when you actually want debugging abilities. the suggested procedure to create these files is:

  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 — picking .dbg as the extension for the debug info file is completely arbitrary, bestie. also the --only-keep-debug step is optional! you could do this instead:
  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. periodt.

note — this switch is only intended for use on fully linked files. it does not make sense 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 is meant for 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 over to the .dwo file, then --strip-dwo to remove those sections from the original .o file 🧹
  • --extract-dwo — extracts the contents of all DWARF .dwo sections. peep the --strip-dwo option above for the full lore.
  • --file-alignment num — sets the file alignment. sections in the file will always start at file offsets that are multiples of this number. defaults to 512. [this option is specific to PE targets.] 🎯
  • --heap reserve / --heap reserve,commit — says how many bytes of memory to reserve (and optionally commit) for use as the 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. that's the lowest memory location used when your program or dll gets loaded. to cut down on relocation and make your dlls faster, 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 — [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 were not 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. after that it's on you, bestie, to decide if the LMA and VMA need updating 😬
  • --stack reserve / --stack reserve,commit — how many bytes of memory to reserve (and optionally commit) for use as the stack for this program. [this option is specific to PE targets.]
  • --subsystem which / --subsystem which:major / --subsystem which:major.minor — specifies the subsystem your program will execute under. the legal values for which are "native", "windows", "console", "posix", "efi-app", "efi-bsd", "efi-rtd", "sal-rtd", and "xbox". you can 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 handy way of shrinking 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 bigger, then it doesn't get compressed. no glow-up, no change 💀
  • --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 🦋
  • --elf-stt-common=yes / --elf-stt-common=no — for ELF files, these control whether common symbols get 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 don't attempt) to shrink any SHT_NOTE type sections by removing duplicate notes 🧚
  • -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 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 🌀

💖 SEE ALSO 💖

okay so when you're done vibing with objcopy, bestie, you are literally gonna want the rest of the squad:

  • ld(1) — the linker, the main character who actually puts your stuff together 🫶
  • objdump(1) — the nosy bestie who reads your object files back to you, iconic 🔍
  • and the Info entries for binutils — the deep lore, the extended universe, the director's cut ✨

ngl, the legal girlies were here first:

Copyright (c) 1991-2025 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, no Front-Cover Texts, and no Back-Cover Texts. fr fr that's the whole deal. 💅

A copy of the license is included in the section entitled "GNU Free Documentation License" — so if you wanna read it, it's right there, no cap. 📜✨

bestie that's the whole page 😭 you made it to the end, I'm so proud of you 🎀 go copy some object files, you absolute legend 👑

this was binutils-2.45.50 vibing from 2025-12-09 — OBJCOPY(1), periodt 💜🦋

📦 where this page comes from