__cyg_profile_func_enter is not called with correct address ?

[Andrew Haley]

robert song wrote:
> Andrew, thank you for your reply.
> Well, the source file can be modified to solve the problem, but I want
> to use one tool to record every address of the running applications
> built with -finstrument-sections option, without modifying the
> application source code itself.

Try this:

void
__cyg_profile_func_enter (void *this_fn, void *call_site)
{
  Dl_info info;
  dladdr(__builtin_return_address(0), &info);

  printf ("addr:%lx %p:%s\n", this_fn, info.dli_saddr, info.dli_sname);
}

Link with -ldl.


> But now the address sometimes may be the PLT address of the application,
> and I don't have a good idea to deal with the problem.
> 
> If the real address can be got in the  __cyg_profile_func_enter()
> function in some way, it will be helpful to analyse.
> 
> 2009/2/26 Andrew Haley <aph@redhat.com>:
>> The shared library loader is trying to make the code as efficient as possible.
>> When you take the address of a symbol in main, the loader is forced to fix up
>> the reloc with a pointer into the PLT.  This happens because at the time the
>> fixup is made, the symbol foo has not been resolved: it'll only be resolved
>> later when the first call to foo happens.  So, we have to use the PLT address
>> because we don't yet know where foo is.
>>
>> Because of C's rule that the address of a function must be unique, every subsequent
>> reference to that symbol will return the PLT address, including the one used
>> in the call to __cyg_profile_func_enter().
>>
>> You can get around this by compiling main with -fpic and not globally initializing
>> ptr.
>>
>> void *ptr;
>>
>> int
>> main (int argc, char *argv[])
>> {
>>  ptr = foo;
>>
>> cc -fpic -finstrument-functions -g -o main main.c tracer.c foo.so -Wl,-rpath `pwd`
>>
>>  $  ./main
>> addr:40073c
>> addr:110634
>> addr:110634
>> addr:11066b
>> addr:11066b
>> addr:40073c
>>
>> Andrew.
>>
>>