Re: [Qemu-devel] [PATCH v2] kvm: Fix enable_cap helpers on older gcc

[Thomas Huth <thuth@linux.vnet.ibm.com>]

On Mon, 12 May 2014 11:51:37 +0200
Alexander Graf <agraf@suse.de> wrote:

> Commit 40f1ee27aa1 introduced handy helpers for enable_cap calls on
> vcpu and vm level. Unfortunately some older gcc versions (4.7.1, 4.6)
> seem to choke on signedness detection in inline created variables:
> 
> target-ppc/kvm.c: In function 'kvmppc_booke_watchdog_enable':
> target-ppc/kvm.c:1302:21: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
> target-ppc/kvm.c: In function 'kvmppc_set_papr':
> target-ppc/kvm.c:1504:21: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
> 
> However - thanks to Thomas Huth for the suggestion - we can just cast the
> offending potentially 0 value to a signed type, making the comparison signed.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> 
> ---
> 
> v1 -> v2:
> 
>   - only do cast, leaving readability intact
> 
> ---
>  include/sysemu/kvm.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index 192fe89..76c39cc 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -302,7 +302,7 @@ int kvm_check_extension(KVMState *s, unsigned int extension);
>          };                                                           \
>          uint64_t args_tmp[] = { __VA_ARGS__ };                       \
>          int i;                                                       \
> -        for (i = 0; i < ARRAY_SIZE(args_tmp) &&                      \
> +        for (i = 0; i < (int)ARRAY_SIZE(args_tmp) &&                 \
>                       i < ARRAY_SIZE(cap.args); i++) {                \
>              cap.args[i] = args_tmp[i];                               \
>          }                                                            \
> @@ -317,7 +317,7 @@ int kvm_check_extension(KVMState *s, unsigned int extension);
>          };                                                           \
>          uint64_t args_tmp[] = { __VA_ARGS__ };                       \
>          int i;                                                       \
> -        for (i = 0; i < ARRAY_SIZE(args_tmp) &&                      \
> +        for (i = 0; i < (int)ARRAY_SIZE(args_tmp) &&                 \
>                       i < ARRAY_SIZE(cap.args); i++) {                \
>              cap.args[i] = args_tmp[i];                               \
>          }                                                            \

Looks much better this way :-)

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>