NM(1) GNU Development Tools NM(1)
NAME
nm - list symbols from object files
SYNOPSIS
nm [-A|-o|--print-file-name] [-a|--debug-syms]
[-B|--format=bsd] [-C|--demangle[=style]]
[-D|--dynamic] [-fformat|--format=format]
[-g|--extern-only] [-h|--help]
[-l|--line-numbers] [--inlines]
[-n|-v|--numeric-sort]
[-P|--portability] [-p|--no-sort]
[-r|--reverse-sort] [-S|--print-size]
[-s|--print-armap] [-t radix|--radix=radix]
[-u|--undefined-only] [-V|--version]
[-X 32_64] [--defined-only] [--no-demangle]
[--plugin name]
[--no-recurse-limit|--recurse-limit]]
[--size-sort] [--special-syms]
[--synthetic] [--with-symbol-versions] [--target=bfdname]
[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 usually local; if uppercase,
the symbol is global (external). There are however a few lowercase symbols that are shown for special global symbols ("u", "v" and "w").
"A" The symbol's value is absolute, and will not be changed by further linking.
"B"
"b" The symbol is in the BSS data section. This section typically contains zero-initialized or uninitialized data, although the exact behavior is system dependent.
"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"
"d" The symbol is in the initialized data section.
"G"
"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" For PE format files this indicates that the symbol is in a section specific to the implementation of DLLs. For ELF format files this indicates that the symbol is an
indirect function. This is a GNU extension to the standard set of ELF symbol types. It indicates a symbol which if referenced by a relocation does not evaluate to its
address, but instead must be invoked at runtime. The runtime execution will then return the value to be used in the relocation.
"I" The symbol is an indirect reference to another symbol.
"N" The symbol is a debugging symbol.
"n" The symbol is in the read-only data section.
"p" The symbol is in a stack unwind section.
"R"
"r" The symbol is in a read only data section.
"S"
"s" The symbol is in an uninitialized or zero-initialized data section for small objects.
"T"
"t" The symbol is in the text (code) section.
"U" The symbol is undefined.
"u" The symbol is a unique global symbol. This is a GNU extension to the standard set of ELF symbol bindings. For such a symbol the dynamic linker will make sure that in
the entire process there is just one symbol with this name and type in use.
"V"
"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. On some systems, uppercase indicates that a default value has
been specified.
"W"
"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.
"?" 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.
--recurse-limit
--no-recurse-limit
--recursion-limit
--no-recursion-limit
Enables or disables a limit on the amount of recursion performed whilst demangling strings. Since the name mangling formats allow for an inifinite level of recursion it is
possible to create strings whose decoding will exhaust the amount of stack space available on the host machine, triggering a memory fault. The limit tries to prevent this
from happening by restricting recursion to 2048 levels of nesting.
The default is for this limit to be enabled, but disabling it may be necessary in order to demangle truly complicated names. Note however that if the recursion limit is
disabled then stack exhaustion is possible and any bug reports about such an event will be rejected.
-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.
-h
--help
Show a summary of the options to nm and exit.
-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.
--inlines
When option -l is active, if the address belongs to a function that was inlined, then this option causes the source information for all enclosing scopes back to the first
non-inlined function to be printed as well. For example, if "main" inlines "callee1" which inlines "callee2", and address is from "callee2", the source information for
"callee1" and "main" will also be printed.
-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.
-r
--reverse-sort
Reverse the order of the sort (whether numeric or alphabetic); let the last come first.
-S
--print-size
Print both value and size of defined symbols for the "bsd" output style. This option has no effect for object formats that do not record symbol sizes, unless --size-sort is
also used in which case a calculated size is displayed.
-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.
-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.
-u
--undefined-only
Display only undefined symbols (those external to 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.
--defined-only
Display only defined symbols for each object file.
--plugin name
Load the plugin called name to add support for extra target types. This option is only available if the toolchain has been built with plugin support enabled.
If --plugin is not provided, but plugin support has been enabled then nm iterates over the files in ${libdir}/bfd-plugins in alphabetic order and the first plugin that claims
the object in question is used.
Please note that this plugin search directory is not the one used by ld's -plugin option. In order to make nm use the linker plugin it must be copied into the
${libdir}/bfd-plugins directory. For GCC based compilations the linker plugin is called liblto_plugin.so.0.0.0. For Clang based compilations it is called LLVMgold.so. The
GCC plugin is always backwards compatible with earlier versions, so it is sufficient to just copy the newest one.
--size-sort
Sort symbols by size. For ELF objects symbol sizes are read from the ELF, for other object types the symbol sizes are 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 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.
--synthetic
Include synthetic symbols in the output. These are special symbols created by the linker for various purposes. They are not shown by default since they are not part of the
binary's original source code.
--with-symbol-versions
Enables the display of symbol version information if any exists. The version string is displayed as a suffix to the symbol name, preceeded by an @ character. For example
foo@VER_1. If the version is the default version to be used when resolving unversioned references to the symbol then it is displayed as a suffix preceeded by two @
characters. For example foo@@VER_2.
--target=bfdname
Specify an object code format other than your system's default format.
@file
Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be
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
ar(1), objdump(1), ranlib(1), and the Info entries for binutils.
COPYRIGHT
Copyright (c) 1991-2020 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, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
binutils-2.34
root@tian:~/tech_learn/multi_thread# cat main.c
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
void print_message_fun(void *ptr);
int main(){
int temp1, tepm2;
void *retval;
pthread_t pth1, pth2;
char *msg1="thread1", *msg2="thread2";
int ret_1, ret_2;
ret_1 = pthread_create(&pth1, NULL, (void *)&print_message_fun, (void *)msg1);
ret_2 = pthread_create(&pth2, NULL, (void *)&print_message_fun, (void *)msg2);
printf("thread 1 return %d\n", pthread_join(pth1, &retval));
printf("thread 1 result：%d\n", (int)retval);
printf("thread 2 return %d\n", pthread_join(pth2, &retval));
printf("thread 2 result：%d\n", (int)retval);
return 0;
}
void print_message_fun(void *ptr){
int i=0;
for( i=0; i<100; i++)
printf("%s:%d \n",(char *)ptr, i);
}
root@tian:~/tech_learn/multi_thread# nm -n -a -C main.o
U _GLOBAL_OFFSET_TABLE_
U printf
U pthread_create
U pthread_join
U __stack_chk_fail
0000000000000000 b .bss
0000000000000000 n .comment
0000000000000000 d .data
0000000000000000 r .eh_frame
0000000000000000 T main
0000000000000000 a main.c
0000000000000000 r .note.gnu.property
0000000000000000 n .note.GNU-stack
0000000000000000 r .rodata
0000000000000000 t .text
000000000000010a T print_message_fun