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

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

[Igor Mammedov]

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)
         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

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

[Michael S. Tsirkin]

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

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

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

[Paolo Bonzini]

On 27/10/21 09:45, 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.

Another possibility is to add a trailing NULL to the array and change 
the loop to "for (i = 0; targets[i]; i++)".

Paolo

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

[Igor Mammedov]

On Wed, 27 Oct 2021 17:59:44 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 27/10/21 09:45, 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.  
> 
> Another possibility is to add a trailing NULL to the array and change 
> the loop to "for (i = 0; targets[i]; i++)".

Thanks,
I've sent v2 with Michael suggested approach,
it seems to me a bit more cleaner.
 
> 
> Paolo
>