Question

I have a C program with a multi-line macro and the program crashes within the macro, how can I pinpoint the location within the macro where the crash happens?

Here is a simplified version of my program. In reality CRASHES is multiple lines long and not easily expandable manually.

#include <stdio.h>
#include <stdarg.h>
#define CRASHES(ptr) \
    (*(ptr) == 123)
main()
{
    char *foo = NULL;
    if (CRASHES(foo))
        printf("This will never happen.");
}

When compiling and running this with gdb a.out I get the expected EXC_BAD_ACCESS (I am on Mac OS X with gdb 6.3), however the crash points to line 8 and not line 4 where the crash is actually caused.

I already tried compiling the program with additional debugging flags -gdwarf-2 and -g3 as suggested by the docs and inserted several assert()s within the macro itself. Unfortunately that did not provide more information.

Answer 1

lots of valuable information here about macro debugging.

…another approach is to use the preprocessor, i.e. compile it using -E and copy-paste the expanded macro into your src-code and see if you can debug from there.