Re: [Qemu-devel] Hacks for building on gcc 7 / Fedora 26

[Eric Blake]

On 07/18/2017 06:59 PM, Richard Henderson wrote:

>> +++ w/hw/usb/bus.c
>> @@ -407,8 +407,9 @@ void usb_register_companion(const char *masterbus,
>> USBPort *ports[],
>>   void usb_port_location(USBPort *downstream, USBPort *upstream, int
>> portnr)
>>   {
>>       if (upstream) {
>> -        snprintf(downstream->path, sizeof(downstream->path), "%s.%d",
>> -                 upstream->path, portnr);
>> +        int l = snprintf(downstream->path, sizeof(downstream->path),
>> "%s.%d",
>> +                         upstream->path, portnr);
>> +        assert(l < sizeof(downstream->path));
> 
> Do you really need an assert there, or will
> 
>     (void)l; /* "used" */
> 
> work as well?  You didn't mention what the reported error is, so I'm
> guessing.

The original error is that gcc 7 complains that snprintf is prone to
buffer overflow if the input is unbounded.  Adding the assert that we
KNOW the input is not unbounded is enough to shut up gcc, on Linux.
What was then drawn into question is whether assert still has that
property on mingw (since assert on mingw lacks the noreturn marking that
it has on Linux).

At this point, unless someone posts an actual failure of gcc 7 compiling
this code for mingw, I don't see why we have to change it; shutting up
the warning on Linux is good enough for the purpose of this patch.

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

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