Why doesn't `-finstrument-functions` work for me?

This is from the gcc manual:

-finstrument-functions

Generate instrumentation calls for entry and exit to functions. Just after func- tion entry and just before function exit, the following profiling functions will be called with the address of the current function and its call site. (On some platforms, __builtin_return_address does not work beyond the current func- tion, so the call site information may not be available to the profiling functions otherwise.)

void __cyg_profile_func_enter (void *this_fn, void *call_site);

void __cyg_profile_func_exit (void *this_fn, void *call_site);

Unless somthing implements those functions, you will get linker errors (which is what happens with MinGW). Conceivably, your GCC version is providing empty implementations.

I got it to work with MinGW GCC by providing this implementation:

#include  <stdio.h>

void __cyg_profile_func_enter (void *this_fn, void *call_site) {
    printf( "entering %p\n", this_fn );
}

void __cyg_profile_func_exit (void *this_fn, void *call_site) {
    printf( "leaving %p\n", this_fn );
}

but this only gives the function addresses. I'd have thought there should be a GCC default implementation of this, but there doesn't seem to be.

People may also be interested in this visualisation of the call tree, which uses the -fintrument-functions flag - caveat, I haven't tried it myself.