Nm (Unix) - Nm Output Sample

Nm Output Sample

/* * File name: test.c * For C code compile with: * gcc -c test.c * * For C++ code compile with: * g++ -c test.c */ int global_var; int global_var_init = 26; static int static_var; static int static_var_init = 25; static int static_function { return 0; } int global_function(int p) { static int local_static_var; static int local_static_var_init=5; local_static_var = p; return local_static_var_init + local_static_var; } int global_function2 { int x; int y; return x+y; } #ifdef __cplusplus extern "C" #endif void non_mangled_function { // I do nothing } int main(void) { global_var = 1; static_var = 2; return 0; }

If the previous code is compiled with the gcc C compiler, the output of nm command would be 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 using the c++ compiler 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 show also an example on how to solve the name mangling problem by using extern "C" in C++ code.