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

["Michael S. Tsirkin" <mst@redhat.com>]

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



>          int i;
>          const char *arch = qtest_get_arch();
>          const char *targets[] = { CONFIG_KVM_TARGETS };
> @@ -942,6 +943,9 @@ bool qtest_has_accel(const char *accel_name)
>                  }
>              }
>          }
> +#else
> +        return false;
> +#endif
>      } else {
>          /* not implemented */
>          g_assert_not_reached();
> -- 
> 2.27.0