On Mon, Aug 7, 2017 at 8:55 AM, Paolo Bonzini <pbonz...@redhat.com> wrote:
> On 07/08/2017 13:36, Greg Kurz wrote:
>> Building QEMU on fedora26 with the latest gcc package fails:
>>
>> CC ppc64-softmmu/target/ppc/kvm.o
>> In file included from include/sysemu/hw_accel.h:16:0,
>> from target/ppc/kvm.c:31:
>> target/ppc/kvm.c: In function ‘kvmppc_booke_watchdog_enable’:
>> include/sysemu/kvm.h:449:35: error: ‘args_tmp[i]’ may be used uninitialized
>> in this function [-Werror=maybe-uninitialized]
>> cap.args[i] = args_tmp[i]; \
>> ^
>> target/ppc/kvm.c: In function ‘kvmppc_set_papr’:
>> include/sysemu/kvm.h:449:35: error: ‘args_tmp[i]’ may be used uninitialized
>> in this function [-Werror=maybe-uninitialized]
>> cc1: all warnings being treated as errors
>>
>> $ rpm -q gcc
>> gcc-7.1.1-3.fc26.ppc64le
>>
>> The compiler should obviously optimize this code away when no extra
>> agument is passed to kvm_vm_enable_cap() and kvm_vcpu_enable_cap(),
>> but it doesn't. This bug should be fixed one day in gcc, but we can
>> also change our code pattern so that we don't hit the issue anymore.
>> We workaround this, by using memcpy() instead of open-coding the copy.
>
> Nice way to do it, thanks. I'll queue it for 2.10.
Indeed :)
>
> Paolo
>
>> Signed-off-by: Greg Kurz <gr...@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4...@amsat.org>
>> ---
>> v2: - use memcpy()
>> ---
>> include/sysemu/kvm.h | 14 ++++----------
>> 1 file changed, 4 insertions(+), 10 deletions(-)
>>
>> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
>> index 91fc07ee9afe..3a458f50e9f4 100644
>> --- a/include/sysemu/kvm.h
>> +++ b/include/sysemu/kvm.h
>> @@ -428,11 +428,8 @@ int kvm_vm_check_extension(KVMState *s, unsigned int
>> extension);
>> .flags = cap_flags, \
>> }; \
>> uint64_t args_tmp[] = { __VA_ARGS__ }; \
>> - int i; \
>> - for (i = 0; i < (int)ARRAY_SIZE(args_tmp) && \
>> - i < ARRAY_SIZE(cap.args); i++) { \
>> - cap.args[i] = args_tmp[i]; \
>> - } \
>> + size_t n = MIN(ARRAY_SIZE(args_tmp), ARRAY_SIZE(cap.args)); \
>> + memcpy(cap.args, args_tmp, n * sizeof(cap.args[0])); \
>> kvm_vm_ioctl(s, KVM_ENABLE_CAP, &cap); \
>> })
>>
>> @@ -443,11 +440,8 @@ int kvm_vm_check_extension(KVMState *s, unsigned int
>> extension);
>> .flags = cap_flags, \
>> }; \
>> uint64_t args_tmp[] = { __VA_ARGS__ }; \
>> - int i; \
>> - for (i = 0; i < (int)ARRAY_SIZE(args_tmp) && \
>> - i < ARRAY_SIZE(cap.args); i++) { \
>> - cap.args[i] = args_tmp[i]; \
>> - } \
>> + size_t n = MIN(ARRAY_SIZE(args_tmp), ARRAY_SIZE(cap.args)); \
>> + memcpy(cap.args, args_tmp, n * sizeof(cap.args[0])); \
>> kvm_vcpu_ioctl(cpu, KVM_ENABLE_CAP, &cap); \
>> })
>>
>>
>
