Question

I’d like to find unused functions in a codebase – including across compilations units. I’m using gcc as my compiler.

Here’s an example:

foo.c (assume appropriate foo.h):

void foo() {
   ....
}

void bar() {
   ....
}

main.c:

#include <stdio.h>
#include "foo.h"  

int main(void)  {
    bar();
    return 0;
}

In this example, I’d like to get warned about foo() not being used.

There is the -Wunused-function gcc option:

-Wunused-function

Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is
enabled by -Wall.

but it’s only for static functions – it won’t produce a warning on the example above.

I’ll also accept suggestions of tools/scripts/other compilers that can do this for me – though I’d prefer to stick with gcc if possible.

Answer 1

Caolan Mc Namara, a LibreOffice developer, has made a small tool to detect this type of thing in LibreOffice source code. They had around thousands functions & methods unused in LibreOffice. His tool is a key element for removing them.

It’s called callcatcher. It can

collect functions/methods defined and subtract called/referenced

It works directly on assembler output and so, it works only for x86 and x86_64 architecture. It can produce output like this. You can integrate it with your traditional compiling and linking call to gcc.

Caolan agrees that it should become a gcc plugin.