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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20131127161308.GA26918@gmail.com>
Date:	Wed, 27 Nov 2013 17:13:08 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.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.


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 27 Nov 2013 16:46:00 +0100
> Ingo Molnar <mingo@...nel.org> wrote:
> 
> > 
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Wed, Nov 27, 2013 at 04:35:19PM +0100, Ingo Molnar wrote:
> > > > So why does GCC then behave like this:
> > > 
> > > I think because its a much saner behaviour; also it might still be the
> > > spec actually says this, its a somewhat opaque text.
> > > 
> > > Anyway, yes GCC seems to behave as we 'expect' it to; I just can't find
> > > the language spec actually guaranteeing this.
> > 
> > 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.

It talks about neither 'arrays' nor 'structures', it talks about 
'aggregates' - which is defined as _both_: 'structures and arrays'.

That's what compiler legalese brings you ;-)

> 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.

I don't think it's grey, I think it's pretty well specified.

> It gets confusing, as the doc also shows:
> 
> struct { int a[3], b; } w[] = { { 1 }, 2 };

I don't think this is valid syntax, I think this needs one more set of 
braces:

 struct { int a[3], b; } w[] = { { { 1 }, 2 } };

> Then points out that w.a[0] is 1 and w.b[0] is 2, and all other 
> elements are zero.

If by 'w.a[0]' you mean 'w[0].a[0]', and if by 'w.b[0]' you mean 
'w[0].b' then yes, this comes from the definition and it's what I'd 
call 'obvious' initialization behavior.

What makes it confusing to you?

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/