3. objcopy

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’]
        [‘-K’ symbolname|‘--keep-symbol=’symbolname]
        [‘-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]
        [‘-W’ symbolname|‘--weaken-symbol=’symbolname]
        [‘-w’|‘--wildcard’]
        [‘-x’|‘--discard-all’]
        [‘-X’|‘--discard-locals’]
        [‘-b’ byte|‘--byte=’byte]
        [‘-i’ interleave|‘--interleave=’interleave]
        [‘-j’ sectionname|‘--only-section=’sectionname]
        [‘-R’ sectionname|‘--remove-section=’sectionname]
        [‘-p’|‘--preserve-dates’]
        [‘--debugging’]
        [‘--gap-fill=’val]
        [‘--pad-to=’address]
        [‘--set-start=’val]
        [‘--adjust-start=’incr]
        [‘--change-addresses=’incr]
        [‘--change-section-address’ section{=,+,-}val]
        [‘--change-section-lma’ section{=,+,-}val]
        [‘--change-section-vma’ section{=,+,-}val]
        [‘--change-warnings’] [‘--no-change-warnings’]
        [‘--set-section-flags’ section=flags]
        [‘--add-section’ sectionname=filename]
        [‘--rename-section’ oldname=newname[,flags]]
        [‘--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]
        [‘--globalize-symbols=’filename]
        [‘--weaken-symbols=’filename]
        [‘--alt-machine-code=’index]
        [‘--prefix-symbols=’string]
        [‘--prefix-sections=’string]
        [‘--prefix-alloc-sections=’string]
        [‘--add-gnu-debuglink=’path-to-file]
        [‘--keep-file-symbols’]
        [‘--only-keep-debug’]
        [‘--extract-symbol’]
        [‘--writable-text’]
        [‘--readonly-text’]
        [‘--pure’]
        [‘--impure’]
        [‘-v’|‘--verbose’]
        [‘-V’|‘--version’]
        [‘--help’] [‘--info’]
        infile [outfile]

The GNU objcopy utility 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. See (ld.info)BFD section `BFD' in Using LD.

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.)

infile

outfile

The input and output files, respectively. If you do not specify outfile, objcopy creates a temporary file and destructively renames the result with the name of infile.

-I bfdname

--input-target=bfdname

Consider the source file's object format to be bfdname, rather than attempting to deduce it. See section Target Selection, for more information.

-O bfdname

--output-target=bfdname

Write the output file using the object format bfdname. See section Target Selection, for more information.

-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. See section Target Selection, for more information.

-B bfdarch

--binary-architecture=bfdarch

Useful when transforming a raw binary 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 sectionname

--only-section=sectionname

Copy only the named section 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.

-R sectionname

--remove-section=sectionname

Remove any section named sectionname from the output file. This option may be given more than once. Note that using this option inappropriately may make the output file unusable.

-S

--strip-all

Do not copy relocation and symbol information from the source file.

-g

--strip-debug

Do not copy debugging symbols or sections from the source file.

--strip-unneeded

Strip all symbols that are not needed for relocation processing.

-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

Keep only symbol symbolname global. Make all other symbols local to the file, so that they are not visible externally. This option may be given more than once.

--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’.

-L symbolname

--localize-symbol=symbolname

Make symbol symbolname local to the file, so that it is not visible externally. This option may be given more than once.

-W symbolname

--weaken-symbol=symbolname

Make symbol symbolname weak. This option may be given more than once.

--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.

-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”.

-x

--discard-all

Do not copy non-global symbols from the source file.

-X

--discard-locals

Do not copy compiler-generated local symbols. (These usually start with ‘L’ or ‘.’.)

-b byte

--byte=byte

Keep only every byteth byte of the input file (header data is not affected). byte can be in the range from 0 to interleave-1, where interleave is given by the ‘-i’ or ‘--interleave’ option, or the default of 4. This option is useful for creating files to program ROM. It is typically used with an srec output target.

-i interleave

--interleave=interleave

Only copy one out of every interleave bytes. Select which byte to copy with the ‘-b’ or ‘--byte’ option. The default is 4. objcopy ignores this option if you do not specify either ‘-b’ or ‘--byte’.

-p

--preserve-dates

Set the access and modification dates of the output file to be the same as those of the input file.

--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.

--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.

--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 of the new file to val. Not all object file formats support setting the start address.

--change-start incr

--adjust-start incr

Change the start address by adding incr. Not all object file formats support setting the start address.

--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.

--change-section-address section{=,+,-}val

--adjust-section-vma section{=,+,-}val

Set or change both the VMA address and the LMA address of the named section. 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 section does not exist in the input file, a warning will be issued, unless ‘--no-change-warnings’ is used.

--change-section-lma section{=,+,-}val

Set or change the LMA address of the named section. 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 section does not exist in the input file, a warning will be issued, unless ‘--no-change-warnings’ is used.

--change-section-vma section{=,+,-}val

Set or change the VMA address of the named section. 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 section does not exist in the input file, a warning will be issued, unless ‘--no-change-warnings’ is used.

--change-warnings

--adjust-warnings

If ‘--change-section-address’ or ‘--change-section-lma’ or ‘--change-section-vma’ is used, and the named section does not exist, issue a warning. This is the default.

--no-change-warnings

--no-adjust-warnings

Do not issue a warning if ‘--change-section-address’ or ‘--adjust-section-lma’ or ‘--adjust-section-vma’ is used, even if the named section does not exist.

--set-section-flags section=flags

Set the flags for the named section. The flags argument is a comma separated string of flag names. The recognized names are ‘alloc’, ‘contents’, ‘load’, ‘noload’, ‘readonly’, ‘code’, ‘data’, ‘rom’, ‘share’, and ‘debug’. You can set the ‘contents’ flag for a section which does not have contents, but it is not meaningful to clear the ‘contents’ flag of a section which does have contents–just remove the section instead. Not all flags are meaningful for all object file formats.

--add-section sectionname=filename

Add a new section named sectionname while copying the file. The contents of the new section are taken from the file filename. The size of the section will be the size of the file. This option only works on file formats which can support sections with arbitrary names.

--rename-section oldname=newname[,flags]

Rename a section from oldname to newname, optionally changing the section's flags to flags in the process. This has the advantage over usng a linker script to perform the rename in that the output stays as an object file and does not become a linked executable.

This option is particularly helpful when the input format is binary, since this will always create a section called .data. If for example, you wanted instead to 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>

--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. 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. 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

Reverse 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. 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. Set 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. Avoid generation of S1/S2 records, creating S3-only record format.

--redefine-sym old=new

Change the name of a symbol old, to new. This can be useful when one is trying link two things together for which you have no source, and there are name collisions.

--redefine-syms=filename

Apply ‘--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

Change 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

Apply ‘--keep-symbol’ option 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

Apply ‘--strip-symbol’ option 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

Apply ‘--strip-unneeded-symbol’ option 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

Apply ‘--keep-global-symbol’ option 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

Apply ‘--localize-symbol’ option 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

Apply ‘--globalize-symbol’ option 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.

--weaken-symbols=filename

Apply ‘--weaken-symbol’ option 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

Mark the output text as writable. This option isn't meaningful for all object file formats.

--readonly-text

Make the output text write protected. This option isn't meaningful for all object file formats.

--pure

Mark the output file as demand paged. This option isn't meaningful for all object file formats.

--impure

Mark the output file as impure. This option isn't meaningful for all object file formats.

--prefix-symbols=string

Prefix all symbols in the output file with string.

--prefix-sections=string

Prefix all section names in the output file with string.

--prefix-alloc-sections=string

Prefix all the names of all allocated sections in the output file with string.

--add-gnu-debuglink=path-to-file

Creates a .gnu_debuglink section which contains a reference to path-to-file and adds it to the output file.

--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.

--only-keep-debug

Strip a file, removing contents of any sections that would not be stripped by ‘--strip-debug’ and leaving the debugging sections intact. In ELF files, this preserves all note sections in the output.

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

Link the executable as normal. Assuming that is is called foo then...
Run objcopy --only-keep-debug foo foo.dbg to create a file containing the debugging info.
Run objcopy --strip-debug foo to create a stripped executable.
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:

Link the executable as normal.
Copy foo to foo.full
Run objcopy --strip-debug foo
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.

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.

--extract-symbol

Keep the file's section flags and symbols but remove all section data. Specifically, the option:

sets the virtual and load addresses of every section to zero;
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.

-V

--version