Re: [Qemu-devel] [PATCH] error: error_setg_errno(): errno gets preserved

[Eric Blake <eblake@redhat.com>]

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On 07/28/2016 09:29 AM, Halil Pasic wrote:

>> You mean va_start, not start_va.  And actually, C11 is clear that errno
>> is unspecified after library functions (but not macros) that don't
>> explicitly state otherwise.  Since va_start() is a macro and not a
>> library function, that means va_start does NOT have carte blanche
>> permission to modify errno.  For more reading on the topic:
> 
> I also considered this function/macro thing but in the end I am not
> aware of anything in C11 what would prohibit va_start to modify errno --
> correct me if I'm wrong. With that it boils down to 'may' and relying on
> 'does not' means you are not covered by the standard C11 (but may
> be covered by something else -- in which case this should be documented
> in HACKING).
> 
>>
>> http://austingroupbugs.net/view.php?id=384
>>
> 
> This got rejected, or? Means that there is no willingness to introduce
> this guarantee at POSIX level?
>  

That particular bug report was rejected because the POSIX folks decided
that the C11 wording was clear enough that va_start() was already
guaranteed to not mess with errno, so no additionally wording was needed
in POSIX.

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


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