6 Representation of #define and #undef

This section describes the stabs support for macro define and undefine information, supported on some systems. (e.g., with -g3 -gstabs when using GCC).

A #define macro-name macro-body is represented with an N_MAC_DEFINE stab with a string field of macro-name macro-body.

An #undef macro-name is represented with an N_MAC_UNDEF stabs with a string field of simply macro-name.

For both N_MAC_DEFINE and N_MAC_UNDEF, the desc field is the line number within the file where the corresponding #define or #undef occurred.

For example, the following C code:

    #define NONE	42
    #define TWO(a, b)	(a + (a) + 2 * b)
    #define ONE(c)	(c + 19)

    main(int argc, char *argv[])
    {
      func(NONE, TWO(10, 11));
      func(NONE, ONE(23));

    #undef ONE
    #define ONE(c)	(c + 23)

      func(NONE, ONE(-23));

      return (0);
    }

    int global;

    func(int arg1, int arg2)
    {
      global = arg1 + arg2;
    }

produces the following stabs (as well as many others):

    .stabs	"NONE 42",54,0,1,0
    .stabs	"TWO(a,b) (a + (a) + 2 * b)",54,0,2,0
    .stabs	"ONE(c) (c + 19)",54,0,3,0
    .stabs	"ONE",58,0,10,0
    .stabs	"ONE(c) (c + 23)",54,0,11,0

NOTE: In the above example, 54 is N_MAC_DEFINE and 58 is N_MAC_UNDEF.