linux-kernel - Re: [PATCH 08/14] sched: add latency tracing for -deadline tasks.

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Message-ID: <20131127160119.GI789@laptop.programming.kicks-ass.net>
Date:	Wed, 27 Nov 2013 17:01:19 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...il.com>,
	tglx@...utronix.de, mingo@...hat.com, oleg@...hat.com,
	fweisbec@...il.com, darren@...art.com, johan.eker@...csson.com,
	p.faure@...tech.ch, linux-kernel@...r.kernel.org,
	claudio@...dence.eu.com, michael@...rulasolutions.com,
	fchecconi@...il.com, tommaso.cucinotta@...up.it,
	nicola.manica@...i.unitn.it, luca.abeni@...tn.it,
	dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...il.com, liming.wang@...driver.com, jkacur@...hat.com,
	harald.gustafsson@...csson.com, vincent.guittot@...aro.org,
	bruce.ashfield@...driver.com
Subject: Re: [PATCH 08/14] sched: add latency tracing for -deadline tasks.

On Wed, Nov 27, 2013 at 10:56:16AM -0500, Steven Rostedt wrote:
> > So from C99 standard §6.7.8 (Initialization)/21:
> > 
> >     "If there are fewer initializers in a brace-enclosed list than 
> >   there are elements or members of an aggregate, or fewer characters 
> >   in a string literal used to initialize an array of known size than 
> >   there are elements in the array, the remainder of the aggregate 
> >   shall be initialized implicitly the same as objects that have static 
> >   storage duration."
> > 
> > static initialization == zeroing in this case.
> > 
> 
> The confusion here is that the above looks to be talking about arrays.
> But it really doesn't specify structures.
> 
> But searching the internet, it looks as though most people believe it
> applies to structures, and any compiler that does otherwise will most
> likely break applications.
> 
> That is, this looks to be one of the gray areas that the compiler
> writers just happen to do what's most sane. And they probably assume
> it's talking about structures as well, hence the lack of warnings.

16 says initializers for aggregate or union types are brace-enclosed
lists. A struct is an aggregate type.


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