what the difference in __cyg_profile_function_enter between gcc and g++? - c++

Question

I know little about __attribute__ and __cyg_profile_function_enter. Of course, they are both GNU C features.
I'm learning C++ to compile Nginx modules. I always try to convert the C code samples to C++.
Here is a simple sample of C:
#include <stdio.h>
int depth_ = -1;
#ifdef __GNUC__
void __cyg_profile_func_enter(void *, void *) __attribute__((no_instrument_function));
void _cyg_profile_func_enter(void *, void *) __attribute__((no_instrument_function));
#define sustainable(fn, caller) \
do {\
printf("%d, %s: fn = %p, caller = %p\n", depth_, __FUNCTION__, fn, caller); \
} while(0)
void __cyg_profile_func_enter(void *fn, void *caller){
printf("Enter:\n");
depth_++;
sustainable(fn, caller);
}
void __cyg_profile_func_exit(void *fn, void *caller){
printf("Exit:\n");
depth_--;
sustainable(fn, caller);
}
#endif
void sustain(){
depth_ = 100;
}
int main(){
depth_ = 10;
sustain();
//Suture suture;
//suture.sultry();
return 0;
}
sh$ gcc -finstrument-functions ...
It displays Enter: 101, __cyg_profile_func_enter: fn = 0x400645, caller = 0x4006ba and Exit: 100, __cyg_profile_func_exit: fn = 0x400645, caller = 0x4006ba circularly
This is the C++ code:
#include <iostream>
using namespace std;
int depth_ = -1;
#ifdef __GNUC__
extern "C" {
void __cyg_profile_func_enter(void *, void *) __attribute__((no_instrument_function));
void __cyg_profile_func_exit(void *, void *) __attribute__((no_instrument_function));
#define sustainable(fn, caller) \
do{ \
printf("%d, %s: fn = %p, caller = %p\n", depth_, __FUNCTION__, fn, caller); \
} while(0)
void __cyg_profile_func_enter(void *fn, void *caller){
printf("Enter:\n");
depth_++;
sustainable(fn, caller);
}
void __cyg_profile_func_exit(void *fn, void *caller){
printf("Exit:\n");
depth_--;
sustainable(fn, caller);
}
}
#endif
void sustain(){
depth_ = 100;
}
class Suture
{
public:
void sultry(){
}
};
int main(int argc, char **argv){
sustain();
Suture suture;
suture.sultry;
}
Then I compile with
sh$ g++ -std=c++11 -finstrument-functions ....
It displays Enter: 2, __cyg_profile_func_enter: fn = 0x400925, caller = 0x40099b and Exit: 1, __cyg_profile_func_exit: fn = 0x400925, caller = 0x40099b circularly.
It's weird. Why the depth_ = 100 works with gcc but not with g++?

Answer 1

What function do you expect fn to be the address of? I'm not seeing function calls in main() that should take place after the assignment of depth_.
If you're seeing repeated calls at all, they must be due to library functions, which could well be performed before the depth_ = 100; assignment.