CODEWITHSUNDEEP
cgccc-preprocessor
Kristoffer
Kristoffer

Reputation: 486

Add unique code to start and end of function in c

I am looking for a way to automatically add code to the start and the beginning of a function. The idea being that i want to profile the running code later. For example i have the functions:

void helloWorld(){
    printf("Hello World!\n");
}

void worldHello(){
    printf("World hello!\n");
}

I would like to have some kind of macro that expands them to:

void helloWorld(){
    printf("Function id 1 enter");
    printf("Hello World!\n");
    printf("Function id 1 exit");
}

void worldHello(){
    printf("Function id 2 enter");
    printf("World hello!\n");
    printf("Function id 2 exit");
}

Where the id is uniquely given each time i use my macro. Do anyoen have any good idea on how i could achieve this? i looked at the "__COUNTER__" in GCC but didnt really get it working as i wanted to.

Upvotes: 3

Views: 2710

Answers (3)

Roman Hocke
Roman Hocke

Reputation: 4239

If You are using GCC, look at -finstrument-functions switch - see https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#index-finstrument-functions It basically calls user-defined function upon entering and leaving any called function. This has some advantages:

  • You don't have to modify Your functions at all.
  • Your code is called no matter how the function exitted (You can have any number of return in Your function and don't care)

Upvotes: 4

mwk
mwk

Reputation: 436

It may be more descriptive to use __func__ rather than __COUNTER__. Here is an example implementation of a macro that does what you want.

#include <stdio.h>

#define WRAPPED_FUNC(funcname, ...) \
    funcname { \
        printf("Function %s entered\n", __func__); \
        __VA_ARGS__ \
        printf("Function %s exited\n", __func__); \
    }

WRAPPED_FUNC(
    void helloWorld(),
    {
        printf("Hello World!\n");
    }
)

WRAPPED_FUNC(
    void worldHello(),
    {
        printf("World hello!\n");
    }
)

int main() {
    helloWorld();
    worldHello();
    return 0;
}

Upvotes: 1

stzahi
stzahi

Reputation: 349

you can use the functions name instead of a number as ID. since function name is unique. for example you can use the macros:

#define START printf( "%s:%d Start \n", __func__, __LINE__)
#define END printf("%s:%d End \n", __func__, __LINE__)

or in kernel:

#define START pr_err(KBUILD_MODNAME ":%s:%d start \n", __func__, __LINE__)
#define END pr_err(KBUILD_MODNAME ":%s:%d end\n", __func__, __LINE__)

Upvotes: 3

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