2. nm

nm [‘-a’|‘--debug-syms’] [‘-g’|‘--extern-only’]
   [‘-B’] [‘-C’|‘--demangle’[=style]] [‘-D’|‘--dynamic’]
   [‘-S’|‘--print-size’] [‘-s’|‘--print-armap’]
   [‘-A’|‘-o’|‘--print-file-name’][‘--special-syms’]
   [‘-n’|‘-v’|‘--numeric-sort’] [‘-p’|‘--no-sort’]
   [‘-r’|‘--reverse-sort’] [‘--size-sort’] [‘-u’|‘--undefined-only’]
   [‘-t’ radix|‘--radix=’radix] [‘-P’|‘--portability’]
   [‘--target=’bfdname] [‘-f’format|‘--format=’format]
   [‘--defined-only’] [‘-l’|‘--line-numbers’] [‘--no-demangle’]
   [‘-V’|‘--version’] [‘-X 32_64’] [‘--help’]  [objfile…]

GNU nm lists the symbols from object files objfile…. If no object files are listed as arguments, nm assumes the file ‘a.out’.

For each symbol, nm shows:

The symbol value, in the radix selected by options (see below), or hexadecimal by default.
The symbol type. At least the following types are used; others are, as well, depending on the object file format. If lowercase, the symbol is local; if uppercase, the symbol is global (external).

A

The symbol's value is absolute, and will not be changed by further linking.

B

The symbol is in the uninitialized data section (known as BSS).

C

The symbol is common. Common symbols are uninitialized data. When linking, multiple common symbols may appear with the same name. If the symbol is defined anywhere, the common symbols are treated as undefined references. For more details on common symbols, see the discussion of –warn-common in (ld.info)Options section `Linker options' in The GNU linker.

D

The symbol is in the initialized data section.

G

The symbol is in an initialized data section for small objects. Some object file formats permit more efficient access to small data objects, such as a global int variable as opposed to a large global array.

I

The symbol is an indirect reference to another symbol. This is a GNU extension to the a.out object file format which is rarely used.

N

The symbol is a debugging symbol.

R

The symbol is in a read only data section.

S

The symbol is in an uninitialized data section for small objects.

T

The symbol is in the text (code) section.

U

The symbol is undefined.

V

The symbol is a weak object. When a weak defined symbol is linked with a normal defined symbol, the normal defined symbol is used with no error. When a weak undefined symbol is linked and the symbol is not defined, the value of the weak symbol becomes zero with no error.

W

The symbol is a weak symbol that has not been specifically tagged as a weak object symbol. When a weak defined symbol is linked with a normal defined symbol, the normal defined symbol is used with no error. When a weak undefined symbol is linked and the symbol is not defined, the value of the symbol is determined in a system-specific manner without error. On some systems, uppercase indicates that a default value has been specified.

-

The symbol is a stabs symbol in an a.out object file. In this case, the next values printed are the stabs other field, the stabs desc field, and the stab type. Stabs symbols are used to hold debugging information. For more information, see Stabs: (stabs.info)Top section `Stabs Overview' in The “stabs” debug format.

?

The symbol type is unknown, or object file format specific.
The symbol name.

The long and short forms of options, shown here as alternatives, are equivalent.

-A
-o
--print-file-name: Precede each symbol by the name of the input file (or archive member) in which it was found, rather than identifying the input file once only, before all of its symbols.
-a
--debug-syms: Display all symbols, even debugger-only symbols; normally these are not listed.
-B: The same as ‘--format=bsd’ (for compatibility with the MIPS nm).
-C
--demangle[=style]: Decode (demangle) low-level symbol names into user-level names. Besides removing any initial underscore prepended by the system, this makes C++ function names readable. Different compilers have different mangling styles. The optional demangling style argument can be used to choose an appropriate demangling style for your compiler. See section c++filt, for more information on demangling.
--no-demangle: Do not demangle low-level symbol names. This is the default.
-D
--dynamic: Display the dynamic symbols rather than the normal symbols. This is only meaningful for dynamic objects, such as certain types of shared libraries.
-f format
--format=format: Use the output format format, which can be bsd, sysv, or posix. The default is bsd. Only the first character of format is significant; it can be either upper or lower case.
-g
--extern-only: Display only external symbols.
-l
--line-numbers: For each symbol, use debugging information to try to find a filename and line number. For a defined symbol, look for the line number of the address of the symbol. For an undefined symbol, look for the line number of a relocation entry which refers to the symbol. If line number information can be found, print it after the other symbol information.
-n
-v
--numeric-sort: Sort symbols numerically by their addresses, rather than alphabetically by their names.
-p
--no-sort: Do not bother to sort the symbols in any order; print them in the order encountered.
-P
--portability: Use the POSIX.2 standard output format instead of the default format. Equivalent to ‘-f posix’.
-S
--print-size: Print size, not the value, of defined symbols for the bsd output format.
-s
--print-armap: When listing symbols from archive members, include the index: a mapping (stored in the archive by ar or ranlib) of which modules contain definitions for which names.
-r
--reverse-sort: Reverse the order of the sort (whether numeric or alphabetic); let the last come first.
--size-sort: Sort symbols by size. The size is computed as the difference between the value of the symbol and the value of the symbol with the next higher value. If the bsd output format is used the size of the symbol is printed, rather than the value, and ‘-S’ must be used in order both size and value to be printed.
--special-syms: Display symbols which have a target-specific special meaning. These symbols are usually used by the target for some special processing and are not normally helpful when included included in the normal symbol lists. For example for ARM targets this option would skip the mapping symbols used to mark transitions between ARM code, THUMB code and data.
-t radix
--radix=radix: Use radix as the radix for printing the symbol values. It must be ‘d’ for decimal, ‘o’ for octal, or ‘x’ for hexadecimal.
--target=bfdname: Specify an object code format other than your system's default format. See section Target Selection, for more information.
-u
--undefined-only: Display only undefined symbols (those external to each object file).
--defined-only: Display only defined symbols for each object file.
-V
--version: Show the version number of nm and exit.
-X: This option is ignored for compatibility with the AIX version of nm. It takes one parameter which must be the string ‘32_64’. The default mode of AIX nm corresponds to ‘-X 32’, which is not supported by GNU nm.
--help: Show a summary of the options to nm and exit.

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