From: Markus Trippelsdorf <markus@trippelsdorf.de>
To: "H. Peter Anvin" <hpa@zytor.com>
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 12:51:09 +0100 [thread overview]
Message-ID: <20161220115109.GB289@x4> (raw)
In-Reply-To: <2966d559-2cea-fd95-76d4-df34192a9b88@zytor.com>
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.
--
Markus
next prev parent reply other threads:[~2016-12-20 11:51 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 [this message]
2016-12-20 18:32 ` hpa
2016-12-20 19:31 ` Markus Trippelsdorf
2016-12-20 20:44 ` H. Peter Anvin
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