Detect compiler and use compiler-specific flags when invoking

Question

I'm handed a variable CC which contains the executable that refers to the compiler on the system. I need to take this executable and eventually call it with some compiler-specific link arguments.

My current approach seems very fragile:

def guess_compiler(cc):
    out = subprocess.check_output((cc, '--version'))
    for possible in (b'clang', b'gcc'):
        if possible in out:
            return possible.decode()
    else:
        # Fall back to gcc
        return 'gcc'

From this I'm using a mapping of the specific linker arguments I care about:

return {
    'clang': '-Wl,-undefined,dynamic_lookup',
    'gcc': '-Wl,--unresolved-symbols=ignore-all',
}[cc]

In short, I'm hoping there's a better (less fragile) way to do what I've accomplished.

For those looking for why I want something like this, it's mostly for portability in a project I'm implementing.

anthony sottile · Accepted Answer · 2017-02-14 00:45:34Z

1

I'd rather call a compiler with some dummy code and these flags passed in. This is also what tools like Autotools and CMake do.

The problem with your current approach is that text string you see in --version output can actually be arbitrary. For instance, when clang wasn't that popular, FreeBSD's cc --version have been giving

GCC 4.2.1 -compatible Clang bla bla

So, just call the compiler with each flag you are interested in and then look at exit code.

An example of how to do this:

for flag in FLAGS:
    try:
        subprocess.check_call((cc, 'test.c', flag), cwd=tmpdir)
        return flag
    except subprocess.CalledProcessError:
        pass
else:
    # wellp, none of them worked, fall back to gcc and they'll get a
    # hopefully reasonable error message
    return FLAG_GCC

edited Feb 14, 2017 at 0:45

anthony sottile

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answered Feb 13, 2017 at 5:30

arrowd

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1 Comment

anthony sottile Over a year ago

Edited with what I attempted to go with :)

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