Re: [Qemu-block] [Qemu-devel] [PATCH v5] build: Work around SIZE_MAX bug in OSX headers

[Programmingkid]

On Oct 11, 2016, at 2:12 PM, Eric Blake wrote:

> On 10/11/2016 01:03 PM, Programmingkid wrote:
> 
>>> +/* Mac OSX has a  bug that incorrectly defines SIZE_MAX with
>>> + * the wrong type. Our replacement isn't usable in preprocessor
>>> + * expressions, but it is sufficient for our needs. */
>>> +#if defined(HAVE_BROKEN_SIZE_MAX) && HAVE_BROKEN_SIZE_MAX
>>> +#undef SIZE_MAX
>>> +#define SIZE_MAX ((size_t)-1)
>>> +#endif
>>> +
> 
>> I have applied your patch to the most recent git commit 
>> (627eae7d729277c84f8e0ac07a8caab39c92c38d) on Mac  OS 10.6.8. QEMU built 
>> without any problems using gcc 4.9.
> 
> Did you also tweak the code to make sure there was an instance of
> printf("%zu", SIZE_MAX) (or similar)? It's not enough that it compiles
> without complaint (although that helps), but also that the
> compiler-warning-on-printf goes away (which we currently don't have any
> in the tree, because we've been writing '"%zu", (size_t)SIZE_MAX' to
> work around the broken headers).

I saw no warnings when I added your printf code. The output was 
18446744073709551615.

Re: [Qemu-block] [Qemu-devel] [PATCH v5] build: Work around SIZE_MAX bug in OSX headers

[Peter Maydell]

On 11 October 2016 at 19:12, Eric Blake  wrote:
> On 10/11/2016 01:03 PM, Programmingkid wrote:
>
>>> +/* Mac OSX has a  bug that incorrectly defines SIZE_MAX with
>>> + * the wrong type. Our replacement isn't usable in preprocessor
>>> + * expressions, but it is sufficient for our needs. */
>>> +#if defined(HAVE_BROKEN_SIZE_MAX) && HAVE_BROKEN_SIZE_MAX
>>> +#undef SIZE_MAX
>>> +#define SIZE_MAX ((size_t)-1)
>>> +#endif
>>> +
>
>> I have applied your patch to the most recent git commit 
>> (627eae7d729277c84f8e0ac07a8caab39c92c38d) on Mac  OS 10.6.8. QEMU built 
>> without any problems using gcc 4.9.
>
> Did you also tweak the code to make sure there was an instance of
> printf("%zu", SIZE_MAX) (or similar)? It's not enough that it compiles
> without complaint (although that helps), but also that the
> compiler-warning-on-printf goes away (which we currently don't have any
> in the tree, because we've been writing '"%zu", (size_t)SIZE_MAX' to
> work around the broken headers).

I have made that check, and tested that the patch causes the
resulting build failure to go away.

I'll apply this to master...

thanks
-- PMM

Re: [Qemu-block] [Qemu-devel] [PATCH v5] build: Work around SIZE_MAX bug in OSX headers

[Eric Blake]

On 10/11/2016 01:03 PM, Programmingkid wrote:

>> +/* Mac OSX has a  bug that incorrectly defines SIZE_MAX with
>> + * the wrong type. Our replacement isn't usable in preprocessor
>> + * expressions, but it is sufficient for our needs. */
>> +#if defined(HAVE_BROKEN_SIZE_MAX) && HAVE_BROKEN_SIZE_MAX
>> +#undef SIZE_MAX
>> +#define SIZE_MAX ((size_t)-1)
>> +#endif
>> +

> I have applied your patch to the most recent git commit 
> (627eae7d729277c84f8e0ac07a8caab39c92c38d) on Mac  OS 10.6.8. QEMU built 
> without any problems using gcc 4.9.

Did you also tweak the code to make sure there was an instance of
printf("%zu", SIZE_MAX) (or similar)? It's not enough that it compiles
without complaint (although that helps), but also that the
compiler-warning-on-printf goes away (which we currently don't have any
in the tree, because we've been writing '"%zu", (size_t)SIZE_MAX' to
work around the broken headers).

> 
> Reviewed-by: John Arbuckle 
> 

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



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Re: [Qemu-block] [Qemu-devel] [PATCH v5] build: Work around SIZE_MAX bug in OSX headers

[Markus Armbruster]

Eric Blake  writes:

> C99 requires SIZE_MAX to be declared with the same type as the
> integral promotion of size_t, but OSX mistakenly defines it as
> an 'unsigned long long' expression even though size_t is only
> 'unsigned long'.  Rather than futzing around with whether size_t
> is 32- or 64-bits wide (which would be needed if we cared about
> using SIZE_T in a #if expression), just hard-code it with a cast.
> This is not a strict C99-compliant definition, because it doesn't
> work in the preprocessor, but if we later need that, the build
> will break on Mac to inform us to improve our replacement at that
> time.
>
> See also https://patchwork.ozlabs.org/patch/542327/ for an
> instance where the wrong type trips us up if we don't fix it
> for good in osdep.h.
>
> Some versions of glibc make a similar mistake with SSIZE_MAX; the
> goal is that the approach of this patch could be copied to work
> around that problem if it ever becomes important to us.
>
> Signed-off-by: Eric Blake 

Reviewed-by: Markus Armbruster