Re: [PATCH] qtest: fix 'expression is always false' build failure in qtest_has_accel()

[Jason Andryuk]

On Wed, Oct 27, 2021 at 4:34 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Wed, Oct 27, 2021 at 03:45:42AM -0400, Igor Mammedov wrote:
> > If KVM is disabled or not present, qtest library build
> > may fail with:
> >    libqtest.c: In function 'qtest_has_accel':
> >       comparison of unsigned expression < 0 is always false
> >       [-Werror=type-limits]
> >          for (i = 0; i < ARRAY_SIZE(targets); i++) {
> >
> > due to empty 'targets' array.
> > Fix it by compiling KVM related part only if
> > CONFIG_KVM_TARGETS is set.
> >
> > Fixes: e741aff0f43343 ("tests: qtest: add qtest_has_accel() to check if 
> > tested binary supports accelerator")
> > Reported-by: Jason Andryuk <jandryuk@gmail.com>
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
>
>
> > ---
> >  tests/qtest/libqtest.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/tests/qtest/libqtest.c b/tests/qtest/libqtest.c
> > index 25aeea385b..9833e16f84 100644
> > --- a/tests/qtest/libqtest.c
> > +++ b/tests/qtest/libqtest.c
> > @@ -931,6 +931,7 @@ bool qtest_has_accel(const char *accel_name)
> >          return false;
> >  #endif
> >      } else if (g_str_equal(accel_name, "kvm")) {
> > +#if defined(CONFIG_KVM_TARGETS)
>
> Ugh.
>         const char *targets[] = { CONFIG_KVM_TARGETS };
>
> are you use CONFIG_KVM_TARGETS is not defined?
>
> Looks like it's defined, just empty.
>
> which is not standard C BTW.
>
> How about we just add an empty string in meson?
>
> diff --git a/meson.build b/meson.build
> index 2c5b53cbe2..ff85e9c2af 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -75,7 +75,7 @@ else
>    kvm_targets = []
>  endif
>
> -kvm_targets_c = ''
> +kvm_targets_c = '""'
>  if not get_option('kvm').disabled() and targetos == 'linux'
>    kvm_targets_c = '"' + '" ,"'.join(kvm_targets) + '"'
>  endif

This allows Debian buster (gcc 8.3.0) to compile.

Thanks,
Jason