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Re: [Qemu-trivial] [Qemu-devel] [PATCH] pci: Fix compiler warning (MinGW

From: Eric Blake
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] pci: Fix compiler warning (MinGW-w64 gcc 4.9)
Date: Thu, 14 May 2015 15:16:50 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05/14/2015 03:06 PM, Eric Blake wrote:
> On 05/14/2015 02:38 PM, Stefan Weil wrote:
>> i686-w64-mingw32-gcc 4.9.1 from Debian Jessie complains:
>> hw/pci/pci.c:938:29: warning:
>>  array subscript is above array bounds [-Warray-bounds]
>> Using g_assert instead of assert fixes this warning.
> Is that because the mingw headers don't properly mark the expansion of
> the failed branch of assert() as noreturn, whereas g_assert() does, and
> therefore the compiler has more information about what variables must be
> if the rest of the function is reached?

> Meanwhile, you may want to file a bug to the mingw maintainers that
> their header is puny when compared to glibc assert() or to glib's
> g_assert, when it comes to giving gcc decent hints.

Oh, I was right!

glibc /usr/include/assert.h:
extern void __assert_fail (const char *__assertion, const char *__file,
                           unsigned int __line, const char *__function)
     __THROW __attribute__ ((__noreturn__));
# define assert(expr)                                                   \
  ((expr)                                                               \
   ? __ASSERT_VOID_CAST (0)                                             \
   : __assert_fail (__STRING(expr), __FILE__, __LINE__, __ASSERT_FUNCTION))

vs mingw /usr/i686-w64-mingw32/sys-root/mingw/include/assert.h:
extern void __cdecl
_assert (const char *_Message, const char *_File, unsigned _Line);
#define assert(_Expression) \
 (void) \
 ((!!(_Expression)) || \

even though mingw has in that same file:
  void __cdecl _Exit(int) __MINGW_ATTRIB_NORETURN;

so it is indeed a bug in the mingw headers that __MINGW_ATTRIB_NORETURN
was not attached to _assert's declaration.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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