Re: [Qemu-devel] [PATCH] kvm: workaround build break on gcc-7.1.1 / fedora26

[Eric Blake]

On 08/03/2017 08:34 AM, Philippe Mathieu-Daudé wrote:
> Hi Greg,
> 
> On 08/02/2017 11:47 AM, 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

> 
> This sizeof() use looks unnatural to me. I wonder why not use size_t,
> since this is about sizeof()/ARRAY_SIZE(). The problem seems to come
> from the commit this cast was introduced (61c7bbd236):
> 
> target-ppc/kvm.c:1302:21: error: comparison of unsigned expression < 0
> is always false [-Werror=type-limits]
> 
> So I'd rather suggest this code, which looks more natural to read to me:
> 
>     if (ARRAY_SIZE(args_tmp)) {
>         for (i = 0; i < ARRAY_SIZE(args_tmp) && ...

For that matter, the existing code is doing:

int i;
i < (int)ARRAY_SIZE(args_tmp)

but wouldn't that be better as:

size_t i;
i < ARRAY_SIZE(args_temp)

I guess we have both the old compilers (per commit 61c7bbd2) and the new
to worry about; although I was unable to reproduce it on Fedora 26 on
x86_64 (is this an architecture-dependent compiler bug?)

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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