How to use -finstrument-functions for C++ programs ?

How to use -finstrument-functions for C++ programs ?

[Dmitry Antipov]

Hello all,

I'm trying to implement a some kind of self-tracing/self-profiling 
feature for the shared
library which should be dlopen()ed and used by the application core. I'm 
started from
simple C program, like this (due to asm, this is x86-specific):

#include <stdio.h>
#include <unistd.h>

#define rdtscll(val) asm volatile ("rdtsc" : "=A" (val))

FILE *f = NULL;
int n, depth = -1;
unsigned long long t;
extern char *program_invocation_short_name;

void __profile_begin (void) __attribute__ 
((constructor,no_instrument_function));
void __profile_end (void) __attribute__ 
((destructor,no_instrument_function));

void __cyg_profile_func_enter (void *, void *) 
__attribute__((no_instrument_function));
void __cyg_profile_func_exit (void *, void *) 
__attribute__((no_instrument_function));

void __profile_begin (void)
{
  char buf[1024];
 
  snprintf (buf, sizeof (buf), "%s.prof.%d", 
program_invocation_short_name, getpid ());
  f = fopen (buf, "w+");
  fprintf (f, "Start of profiling for %s.\n", 
program_invocation_short_name);
}

void __profile_end (void)
{
  fprintf (f, "End of profiling for %s.\n", program_invocation_short_name);
  fclose (f);
}

void __cyg_profile_func_enter (void *func,  void *caller)
{
  rdtscll (t);
  depth++;
  for (n = 0; n < depth; n++)
    fprintf (f, " ");
  fprintf (f, "-> %p %llu\n", func, t);
}

void __cyg_profile_func_exit (void *func, void *caller)
{
  rdtscll (t);
  for (n = 0; n < depth; n++)
    fprintf (f, " ");
  fprintf (f, "<- %p %llu\n", func, t);
  depth--;
}

void foo (void)
{
}

void bar (void)
{
}

int main (int argc, char *argv[])
{
  foo ();
  bar ();
  return 0;
}


When compiling as a C program (with 'gcc -finstrument-functions -o 
selfprof selfprof.c'),
it works as expected, i.e. outputs into selfprof.prof.xxxxx something 
like this:

Start of profiling for selfprof.
-> 0x80487b0 1521198259227518
 -> 0x8048750 1521198259234666
 <- 0x8048750 1521198259245630
 -> 0x8048780 1521198259248230
 <- 0x8048780 1521198259250462
<- 0x80487b0 1521198259252738
End of profiling for selfprof.

Here I can check that my code:
 - enters main()
 - enters foo()
 - leaves foo()
 - enters bar()
 - leaves bar()
 - leaves main()

But, when compiling the same code as C++ program (with 'g++ 
-finstrument-functions -o
selfprof selfprof.cxx', I've no function entry/exit marks in output:

Start of profiling for selfprof.
End of profiling for selfprof.

I've checked this behaviour both with gcc 3.3.3 (preinstalled on my 
Fedora Core 2 system)
and with gcc 3.4.3 bootstrapped by myself from sources, but results are 
the same.

So, I'm confused. Can anybody explain me why this feature doesn't work 
for C++ programs ?

Thanks,
Dmitry

P.S. Please also reply to me directly if possible.

Re: How to use -finstrument-functions for C++ programs ?

[Mohammed ElShoukry]

You have to declare them extern "C" before using them in C++ programs.

Mohammed