1. Technology
Send to a Friend via Email
Linux / Unix Command: nm
Command Library

NAME

nm - list symbols from object files  

SYNOPSIS

nm [-a|--debug-syms] [-g|--extern-only]
   [-B] [-C|--demangle[=style]] [-D|--dynamic]
   [-S|--print-size] [-s|--print-armap]
   [-A|-o|--print-file-name]
   [-n|-v|--numeric-sort] [-p|--no-sort]
   [-r|--reverse-sort] [--size-sort] [-u|--undefined-only]
   [-t radix|--radix=radix] [-P|--portability]
   [--target=bfdname] [-fformat|--format=format]
   [--defined-only] [-l|--line-numbers] [--no-demangle]
   [-V|--version] [-X 32_64] [--help]  [objfile...]  

DESCRIPTION

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.
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 weak symbol becomes zero with no error.
-
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.
?
The symbol type is unknown, or object file format specific.
*
The symbol name.
 

OPTIONS

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.
--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 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. The size of the symbol is printed, rather than the value.
-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.
-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.
 

SEE ALSO

ar(1), objdump(1), ranlib(1), and the Info entries for binutils.  

Important: Use the man command (% man) to see how a command is used on your particular computer.

>> Linux/Unix Command Library

>> Shell Command Library

You can opt-out at any time. Please refer to our privacy policy for contact information.

Discuss in my forum

©2014 About.com. All rights reserved.