CODEWITHSUNDEEP
cunit-testinggccgcov
user2941479
user2941479

Reputation:

Wrapping open() for unit testing will make gcov not able to open gcda file

I am in the process of implementing using testing for some C program. For this purpose I am using GCC's -Wl,--wrap=open in order to mock stdlib's open() function and to check that it has been called with the correct options.

When doing so however gcov is having some issues in writing its .gcda file. I guess the mock I define is not only used by my tests but also by gcov. Here is a small example of how to reproduce this:

#include <stdio.h>

int __wrap_open(const char *path, int flags, int mode)
{
    printf("hello from __wrap_open\n");
    return -1;
}


int main(void)
{
    return 0;
}

And compile it with gcc main.c -Wl,--wrap=open -fprofile-arcs -ftest-coverage -lgcov. In order to keep the example simple I have removed the unit testing part using CMocka in order to show the bug I am encountering.

When running the executable a.out I have the following output with GCC and gcov 6.3.0:

$ ./a.out
hello from __wrap_open
hello from __wrap_open
profiling:/home/romain/wrap-bug/main.gcda:Cannot open

Is there a way to mock the open() function for my unit testing purposes and to be able to use gcov in order to generate code coverage data? Maybe there is a way to tell gcov to use __real_open()?

Upvotes: 4

Views: 1490

Answers (1)

Ctx
Ctx

Reputation: 18430

An easy way to accomplish that would be:

  • Check, if the path of the file passed to open() is your profiling file
  • if yes, pass the call to __real_open()

i.e.

int __real_open(const char *path, int flags, int mode);

int __wrap_open(const char *path, int flags, int mode)
{
    if (strlen(path) > 5 && !strcmp(path + strlen(path) - 5, ".gcda"))
        return __real_open(path, flags, mode);
    printf("hello from __wrap_open\n");
    return -1;
}

Using this way you can of course add more files, which should not be tampered with, easily.

Upvotes: 2

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