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

[Eric Blake]

On 07/17/2017 12:36 PM, Peter Maydell wrote:
> On 17 July 2017 at 18:29, Eric Blake <address@hidden> wrote:
>> On 07/17/2017 11:46 AM, Dr. David Alan Gilbert 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));
>>>
>>> You may find this doesn't help in some windows builds;  the assert
>>> functions aren't always marked as noreturn (because they pop up a dialog
>>> that asks you whether you want to run into a debugger etc).
>>
>> How would it not help?  Are we using gcc 7 on windows builds?
> 
> At some point in the future we are likely to, because my
> w32/w64 test setups use the Ubuntu gcc-mingw-w64-x86-64
> packages, and so as I upgrade my desktop they will move
> forward to newer gcc versions. (More generally our users
> may do so before me ;-))

So, does gcc's warning actually depend on the no-return-ness of the
assert() statement added here?

Would there be anything wrong with making osdep.h do this on mingw:

#include <assert.h>
#undef assert
#define assert(expr) g_assert(expr)

so that we can reliably get no-return handling that we desire, without
having to audit lots of other code?

> 
> We should be consistent -- if we can't trust assert() to
> be marked nonreturn, as it seems we can't, then we shouldn't
> write new code that assumes it always is, even if today
> it doesn't happen to bite us on the compiler/host combinations
> we're testing right now.

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

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