Re: [PATCH for-5.2] configure: Make "does libgio work" test pull in some actual functions

[Paolo Bonzini <pbonzini@redhat.com>]

On 16/11/20 11:46, Peter Maydell wrote:
> In commit 76346b6264a9b01979 we tried to add a configure check that
> the libgio pkg-config data was correct, which builds an executable
> linked against it.  Unfortunately this doesn't catch the problem
> (missing static library dependency info), because a "do nothing" test
> source file doesn't have any symbol references that cause the linker
> to pull in .o files from libgio.a, and so we don't see the "missing
> symbols from libmount" error that a full QEMU link triggers.
> 
> (The ineffective test went unnoticed because of a typo that
> effectively disabled libgio unconditionally, but after commit
> 3569a5dfc11f2 fixed that, a static link of the system emulator on
> Ubuntu stopped working again.)
> 
> Improve the gio test by having the test source fragment reference a
> g_dbus function (which is what is indirectly causing us to end up
> wanting functions from libmount).
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> The ideal thing here might perhaps be to force the linker to
> pull in everything in the library rather than trusting that
> this particular function is sufficient to trigger the need
> for libmount functions, but annoyingly gcc and clang
> have different command line options to do that.
> 
>   configure | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/configure b/configure
> index 4cef321d9dc..2717cf1db0a 100755
> --- a/configure
> +++ b/configure
> @@ -3512,8 +3512,15 @@ if $pkg_config --atleast-version=$glib_req_ver gio-2.0; then
>       # Check that the libraries actually work -- Ubuntu 18.04 ships
>       # with pkg-config --static --libs data for gio-2.0 that is missing
>       # -lblkid and will give a link error.
> -    write_c_skeleton
> -    if compile_prog "" "$gio_libs" ; then
> +    cat > $TMPC <<EOF
> +#include <gio/gio.h>
> +int main(void)
> +{
> +    g_dbus_proxy_new_sync(0, 0, 0, 0, 0, 0, 0, 0);
> +    return 0;
> +}
> +EOF
> +    if compile_prog "$gio_cflags" "$gio_libs" ; then
>           gio=yes
>       else
>           gio=no
> 

Looks good,

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo