Best practices for probing for symbol visibility extensions in autoconf

Question

I'd like to add symbol hiding for internal symbols to an existing library with an autoconf-based build system. What's the best way to probe for the local compiler's equivalent for -fvisibility=hidden and __attribute__ ((visibility("default")))?

Answer 1

I don't think there is a standard macro for this, but here is something which you should be able to extend to support other compilers as needed, e.g. __hidden for Sun compilers:

AC_CACHE_CHECK([for __attribute__((visibility("hidden")))],
    ac_cv_hidden_visibility_attribute, [
    echo 'int __attribute__ ((visibility ("hidden"))) foo (void) { return 1; }' > conftest.c
    ac_cv_hidden_visibility_attribute=no
    if AC_TRY_COMMAND(${CC-cc} -Werror -S conftest.c -o conftest.s 1>&AS_MESSAGE_LOG_FD);
    then
        if grep '\.hidden.*foo' conftest.s >/dev/null;
        then
            ac_cv_hidden_visibility_attribute=yes
        fi
    fi
    rm -f conftest.*
    ])
if test $ac_cv_hidden_visibility_attribute = yes;
then
    AC_DEFINE(HAVE_HIDDEN_VISIBILITY_ATTRIBUTE, 1,
          [Define if __attribute__((visibility("hidden"))) is supported.])
fi

The resulting config.h:

/* Define if __attribute__((visibility("hidden"))) is supported. */
#define HAVE_HIDDEN_VISIBILITY_ATTRIBUTE 1