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From: hpa@zytor.com
To: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org,
	mingo@kernel.org, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/tools: Fix gcc-7 warning in relocs.c
Date: Tue, 20 Dec 2016 10:32:58 -0800	[thread overview]
Message-ID: <20577F06-9AE8-4760-9F38-45711025D6FB@zytor.com> (raw)
In-Reply-To: <20161220115109.GB289@x4>

On December 20, 2016 3:51:09 AM PST, Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
>On 2016.12.20 at 03:10 -0800, H. Peter Anvin wrote:
>> On 12/20/16 02:00, Markus Trippelsdorf wrote:
>> > On 2016.12.20 at 01:30 -0800, H. Peter Anvin wrote:
>> >> I'd strongly prefer a non-data-dependent solution, specifically
>adding
>> >> at the top of sort_relocs():
>> >>
>> >> if (!r->count)
>> >> 	return;
>> >>
>> >> However, by my reading of the C and POSIX standards, this is a gcc
>> >> error: qsort() should do nothing if the count is zero.
>> > 
>> > No, it is invoking undefined behavior. 
>> 
>> > Notice the nonnull attribute in /usr/include/stdlib.h:
>> > 
>> > 739 /* Sort NMEMB elements of BASE, of SIZE bytes each,
>> > 740    using COMPAR to perform the comparisons.  */
>> > 741 extern void qsort (void *__base, size_t __nmemb, size_t __size,
>> > 742                    __compar_fn_t __compar) __nonnull ((1, 4));
>> > 
>> > But feel free to revert my patch and add your solution.
>> 
>> Well, s/gcc/glibc/ then.
>> 
>> >        The  qsort()  function  shall sort an array of nel objects,
>the
>> >        initial element of which is pointed to by base
>
>NULL does not point to any object, therefore it is UB.

That seems, quite frankly, like a pretty idiotic lawyerism.  Why would a pointer that by spec is never referenced not be able to be null?
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

  reply	other threads:[~2016-12-20 18:33 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-15 12:45 [PATCH] x86-64: Fix gcc-7 warning in relocs.c Markus Trippelsdorf
2016-12-19 10:56 ` [tip:x86/urgent] x86/tools: " tip-bot for Markus Trippelsdorf
2016-12-20  9:30   ` H. Peter Anvin
2016-12-20 10:00     ` Markus Trippelsdorf
2016-12-20 11:10       ` H. Peter Anvin
2016-12-20 11:51         ` Markus Trippelsdorf
2016-12-20 18:32           ` hpa [this message]
2016-12-20 19:31             ` Markus Trippelsdorf
2016-12-20 20:44               ` H. Peter Anvin

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