nm (
name mangling
In compiler construction, name mangling (also called name decoration) is a technique used to solve various problems caused by the need to resolve unique names for programming entities in many modern programming languages.
It provides a way of e ...
) is a
Unix
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...
command used to dump the
symbol table
In computer science, a symbol table is a data structure used by a language translator such as a compiler or interpreter, where each identifier (or symbols), constants, procedures and functions in a program's source code is associated with inf ...
and their attributes from a
binary
Binary may refer to:
Science and technology Mathematics
* Binary number, a representation of numbers using only two digits (0 and 1)
* Binary function, a function that takes two arguments
* Binary operation, a mathematical operation that ta ...
executable
In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instructions", as opposed to a data fil ...
file (including
libraries
A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...
, compiled
object modules, shared-object files, and standalone
executable
In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instructions", as opposed to a data fil ...
s).
The output from
nm distinguishes between various symbol types. For example, it differentiates between a
function that is supplied by an object module and a function that is required by it.
nm is used as an aid for
debugging
In computer programming and software development, debugging is the process of finding and resolving ''bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems.
Debugging tactics can involve in ...
, to help resolve problems arising from name conflicts and
C++ name mangling, and to validate other parts of the
toolchain
In software, a toolchain is a set of programming tools that is used to perform a complex software development task or to create a software product, which is typically another computer program or a set of related programs. In general, the tools for ...
.
This command is shipped with a number of later versions of
Unix
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...
and
similar operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
s including
Plan 9 Plan 9 or Plan Nine may refer to:
Music
* Plan 9 (band), a psychedelic rock band from Rhode Island
* ''Plan 9'', an album by Big Guitars From Memphis with Rick Lindy
* "Plan 9", a song on the 1993 album ''Gorgeous'' by electronica band 808 Stat ...
. The
GNU Project
The GNU Project () is a free software, mass collaboration project announced by Richard Stallman on September 27, 1983. Its goal is to give computer users freedom and control in their use of their computers and Computer hardware, computing devi ...
ships an implementation of
nm as part of the
GNU Binutils
The GNU Binary Utilities, or , are a set of programming tools for creating and managing binary programs, object files, libraries, profile data, and assembly source code.
Tools
They were originally written by programmers at Cygnus Solutions ...
package.
nm output sample
/*
* File name: test.c
* For C code compile with:
* gcc -c test.c
*
* For C++ code compile with:
* g++ -c test.cpp
*/
int global_var;
int global_var_init = 26;
static int static_var;
static int static_var_init = 25;
static int static_function()
int global_function(int p)
int global_function2()
#ifdef __cplusplus
extern "C"
#endif
void non_mangled_function()
int main(void)
If the previous code is compiled with the
gcc C compiler, the output of the
nm command is the following:
# nm test.o
0000000a T global_function
00000025 T global_function2
00000004 C global_var
00000000 D global_var_init
00000004 b local_static_var.1255
00000008 d local_static_var_init.1256
0000003b T main
00000036 T non_mangled_function
00000000 t static_function
00000000 b static_var
00000004 d static_var_init
When the C++ compiler is used, the output differs:
# nm test.o
0000000a T _Z15global_functioni
00000025 T _Z16global_function2v
00000004 b _ZL10static_var
00000000 t _ZL15static_functionv
00000004 d _ZL15static_var_init
00000008 b _ZZ15global_functioniE16local_static_var
00000008 d _ZZ15global_functioniE21local_static_var_init
U __gxx_personality_v0
00000000 B global_var
00000000 D global_var_init
0000003b T main
00000036 T non_mangled_function
The differences between the outputs also show an example of solving the name mangling problem by using
extern "C"
The C and C++ programming languages are closely related but have many significant differences. C++ began as a fork of an early, pre- standardized C, and was designed to be mostly source-and-link compatible with C compilers of the time. Due to ...
in C++ code.
See also
*
Objdump
objdump is a command-line program for displaying various information about object files on Unix-like operating systems. For instance, it can be used as a disassembler to view an executable in assembly form. It is part of the GNU Binutils for fine- ...
External links
*
*
Unix programming tools
Unix SUS2008 utilities
Articles with example C code
Plan 9 commands
{{unix-stub