How to check behaviourally for gcov instrumentation

[detly]

My library needs to measure code coverage for tests that call abort(). The way this is typically done with GCC and gcov is to call a special gcov function in the signal handler for SIGABRT:

#include <gcov.h>
#include <signal.h>

static void flush_gcov(int signum)
{
    __gcov_dump();
    signal(signum, SIG_DFL);
    raise(signum);
}

int main(void)
{
    (void) signal(SIGABRT, flush_gcov);
    return 0;
}

This works fine! But it can only be compiled when gcov instrumentation is enabled. So instead, I have something like:

main.c:

#include "shim.h"

int main(void)
{
    shim_init();
    return 0;
}

shim.h:

#ifndef SHIM_H
#define SHIM_H

void shim_init(void);

#endif // SHIM_H

shim_gcov.c:

#include <gcov.h>
#include <signal.h>

#include <stdio.h>

#include "shim.h"

static void flush_gcov(int signum)
{
    __gcov_dump();
    signal(signum, SIG_DFL);
    raise(signum);
}

void shim_init(void)
{
    (void) signal(SIGABRT, flush_gcov);
    printf("I believe in unicorns!\n");
}

shim_none.c:

#include "shim.h"

#include <stdio.h>

void shim_init(void)
{
    printf("I have never met a unicorn :(\n");
}

So if I'm building for coverage specifically with GCC and gcov, I want to use shim_gcov.c. If I'm not, I want to use shim_none.c. The problem is I can't find a way to test this "behaviourally". By that I mean, I can do:

if c_compiler.get_id() == 'gcc' and get_option('b_coverage')
    gcov_test_files += files('shim_gcov.c')
else
    gcov_test_files += files('shim_none.c')
endif

...but it's entirely possible to generate a build for GCC + lcov, or even have both missing (Meson generates a warning but the project will build fine). In those cases, this check will be incorrect. It seems like it would be more sensible to use eg.

if c_compiler.has_function('__gcov_dump', prefix : ['#include <gcov.h>'])

...but this is always false, whether b_coverage is true or false. Another attempt was:

if c_compiler.has_header('gcov.h')

...but that is always true.

How can I check for the availability of gcov's functions here?

For reproducability here's the full meson.build I use for this test:

meson.build:

project(
    'gcov-meson-test', 'c',
    meson_version: '>=1.3.0',
    default_options: ['c_std=c11']
)

c_compiler = meson.get_compiler('c')

gcov_test_files = files('main.c')

# if c_compiler.get_id() == 'gcc' and get_option('b_coverage')
# if c_compiler.has_header('gcov.h')
if c_compiler.has_function('__gcov_dump', prefix : ['#include <gcov.h>'])
    message('Using GCOV shim')
    gcov_test_files += files('shim_gcov.c')
else
    message('Using no shim')
    gcov_test_files += files('shim_none.c')
endif

gcov_test_prog = executable(
    'gcov_test',
    sources : gcov_test_files,
)

[detly]

I ended up raising #13610 based on this.