linux-kernel - Re: Q: why didn't GCC warn about this uninitialized variable? (was: Re: [PATCH] perf tests: initialize sa.sa

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Date:	Thu, 3 Mar 2016 14:46:25 +0100
From:	Jakub Jelinek <jakub@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Colin King <colin.king@...onical.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Richard Henderson <rth@...ddle.net>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Q: why didn't GCC warn about this uninitialized variable? (was:
 Re: [PATCH] perf tests: initialize sa.sa_flags)

On Thu, Mar 03, 2016 at 02:24:34PM +0100, Ingo Molnar wrote:
> 6 hours of PeterZ time translates to quite a bit of code restructuring overhead to 
> eliminate false positive warnings...

I'll file a bugzilla enhancement request for this (with new attribute),
perhaps we could do it in FRE that is able to see through memory
stores/loads even in addressable structures in some cases.
Though, certainly GCC 7 material.
And, in this particular case it couldn't do anything anyway, because
the sigfillset call is not inlined, and takes address of a field in the
structure.  The compiler can't know if it doesn't cast it back to struct
sigaction and initialize the other fields.
BTW, valgrind should be able to detect this.

	Jakub