STRIP(1)

NAME
strip - remove symbols

SYNOPSIS
strip [ option ] name ...

DESCRIPTION
strip removes or modifies the symbol table attached to the output of the assembler and link editor. This is useful to save space after a program has been debugged and to limit dynamically bound symbols.

strip no longer removes relocation entries under any condition. Instead, it updates the external relocation entries (and indirect symbol table entries) to reflect the resulting symbol table. strip prints an error message for those symbols not in the resulting symbol table that are needed by an external relocation entry or an indirect symbol table. The link editor ld(1) is the only program that can strip relocation entries and know if it is safe to do so.

When strip is used with no options on an executable file, it checks that file to see if it uses the dynamic link editor. If it does, the effect of the strip command is the same as using the -u and -r options. If the file does not use the dynamic link editor, the effect of strip without any options is the same as using the -s option of ld(1). The options -S, -x, and -X have the same effect as the ld(1) options. The options to strip(1) can be combined to trim the symbol table to just what is desired.

You should trim the symbol table of files used with dynamic linking so that only those symbols intended to be external interfaces are saved. Files used with dynamic linking include executables, objects that are loaded (usually bundles), and dynamic shared libraries. Only global symbols are used by the dynamic linking process. You should strip all non-global symbols.

When an executable is built with all its dependent dynamic shared libraries, it is typically stripped with:
    % strip -u -r executable
which saves all undefined symbols (usually defined in the dynamic shared libraries) and all global symbols defined in the executable referenced by the dynamic libraries (as marked by the static link editor when the executable was built). This is the maximum level of striping for an executable that will still allow the program to run correctly with its libraries.

If the executable loads objects, however, the global symbols that the objects reference from the executable also must not be stripped. In this case, you should list the global symbols that the executable wants to allow the objects to reference in a file, and those global symbols are then saved when the executable is stripped. For example:
    % strip -u -r -s interface_symbols executable
where the file interface_symbols would contain only those global symbols from the executable that the executable wants the loaded objects to have access to.

For objects that will be loaded into an executable, you should trim the symbol table to limit the global symbols the executable will see. This would be done with:
    % strip -s interface_symbols -u object
which would leave only the undefined symbols and symbols listed in the file interface_symbols in the object file. In this case, strip(1) has updated the relocation entries and indirect symbol table to reflect the new symbol table.

For dynamic shared libraries, the maximum level of stripping is usually -x (to remove all non-global symbols).

STRIPPING FILES FOR USE WITH RUNTIME LOADED CODE

Trimming the symbol table for programs that load code at runtime allows you to control the interface that the executable wants to provide to the objects that it will load; it will not have to publish symbols that are not part of its interface. For example, an executable that wishes to allow only a subset of its global symbols but all of the statically linked shared library's globals to be used would be stripped with:
    % strip -s interface_symbols -A executable
where the file interface_symbols would contain only those symbols from the executable that it wishes the code loaded at runtime to have access to. Another example is an object that is made up of a number of other objects that will be loaded into an executable would built and then stripped with:
    % ld -o relocatable.o -r a.o b.o c.o
    % strip -s interface_symbols -u relocatable.o
which would leave only the undefined symbols and symbols listed in the file interface_symbols in the object file. In this case strip(1) has updated the relocation entries to reflect the new symbol table.

OPTIONS

The first set of options indicate symbols that are to be save in the resulting output file.

-u  Save all undefined symbols. This is intended for use with relocatable objects to save symbols referred to by external relocation entries. Note that common symbols are also referred to by external relocation entries and this flag does not save those symbols.

-r  Save all symbols referenced dynamically.

-s filename
    Save the symbol table entries for the global symbols listed in filename. The symbol names listed in filename must be one per line. Leading and trailing white space are not part of the symbol name. Lines starting with # are ignored, as are lines with only white space.

-R filename
    Remove the symbol table entries for the global symbols listed in filename. This file has the same format as the -s filename option above. This option is usually used in combination with other options that save some symbols, -S, -x, etc.

-i  Ignore symbols listed in the -s filename or -R filename options that are not in the files to be stripped (this is normally an error).

-d filename
    Save the debugging symbol table entries for each source file name listed in filename. The source file names listed in filename must be one per line with no other white space in the file except the newlines on the end of each line. And they must be just the base name of the source file without any leading directories. This option works only with the stab(5) debugging format, it has no affect when using the DWARF debugging format.

-A  Save all global absolute symbols except those with a value of zero, and save Objective C class symbols. This is intended for use of programs that load code at runtime and want the loaded code to use symbols from the shared libraries (this is only used with NEXTSTEP 3.3 and earlier releases).

-n  Save all N_SECT global symbols. This is intended for use with executable programs in combination with -A to remove the symbols needed for correct static link editing which are not needed for use with runtime loading interfaces where using the -s filename would be too much trouble (this is only used with NEXTSTEP 3.3 and earlier releases).

These options specify symbols to be removed from the resulting output file.

-S  Remove the debugging symbol table entries (those created by the -g option to cc(1) and other compilers).

-X  Remove the local symbols whose names begin with `L'.

-T  The intent of this flag is to remove Swift symbols. It removes the symbols whose names begin with `_$S' or `_$s' only when it finds an __objc_imageinfo section with and it has a non-zero swift version. The future the implementation of this flag may change to match the intent.

-N  In binaries that use the dynamic linker remove all nlist symbols and the string table. Setting the environment variable STRIP_NLISTS has the same effect.

-x  Remove all local symbols (saving only global symbols).

-c  Remove the section contents of a dynamic library creating a stub library output file.

And the last options:

-   Treat all remaining arguments as file names and not options.

-o output
    Write the result into the file output.

-no_uuid
    Remove any LC_UUID load commands.

-no_split_info
    Remove the LC_SEGMENT_SPLIT_INFO load command and its payload load.

-no_code_signature_warning
    Don't warn when the code signature would be invalid in the output.

-arch arch_type
    Specifies the architecture, arch_type, of the file for strip(1) to operate on when the file is a universal file. (See arch(3) for the currently know arch_types.) The arch_type can be "all" to operate on all architectures in the file, which is the default.

SEE ALSO
ld(1), cc(1)

EXAMPLES

When creating a stub library the -c and -x are typically used:

    strip -x -c libfoo -o libfoo.stripped

LIMITATIONS
Not every layout of a Mach-O file can be stripped by this program. But all layouts produced by the Apple compiler system can be stripped.