From: Jens Gustedt <jens.gustedt@inria.fr>
To: musl@lists.openwall.com
Subject: Re: Results of static analysis with clang static analyser
Date: Thu, 24 Sep 2015 09:22:34 +0200 [thread overview]
Message-ID: <1443079354.23868.25.camel@inria.fr> (raw)
In-Reply-To: <20150924003442.GG17773@brightrain.aerifal.cx>
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Am Mittwoch, den 23.09.2015, 20:34 -0400 schrieb Rich Felker:
> On Wed, Sep 23, 2015 at 10:02:51PM +0200, Jens Gustedt wrote:
> > The one in pthread_create I always struggle with. I remember that I
> > had myself once convinced (or was it you?) that the bad case can't
> > happen, but I was not able to reproduce the argument spontaneously.
>
> From my perspective, this one is simply a bug in the static analysis.
> At line 218, pointer arithmetic was performed on `stack` to get `tsd`.
> If `stack` were null this would be UB, and if `stack` is not null then
> you cannot get a null pointer without the arithmetic having invoked
> UB, so you can conclude that `tsd` is not null.
I wouldn'd call this a bug. This also assumes that the analyser has do
"know" from somewhere that `stack` is a pointer that is sufficiently
far from the 0 address, so the result of the arithmetic can never be a
0 valued pointer.
So the problem here is that we use a pointer value that is the result
of arithmetic to hold the state of a conditional execution.
AFAICS, we could completely avoid that by placing a goto after line
220 to jump to line 251. Then the initialization of tsd and the `if
(!tsd)` conditional (not the code inside) could be omitted.
Jens
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next prev parent reply other threads:[~2015-09-24 7:22 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-23 5:58 Khem Raj
2015-09-23 19:38 ` Rich Felker
2015-09-23 20:02 ` Jens Gustedt
2015-09-24 0:34 ` Rich Felker
2015-09-24 7:22 ` Jens Gustedt [this message]
2015-09-24 8:51 ` [PATCH] help static analysis by avoiding to hold state in a pointer that is subject to arithmetic Jens Gustedt
2015-09-25 15:35 ` Results of static analysis with clang static analyser Matt Avery
2015-09-25 21:37 ` Jens Gustedt
2015-09-23 20:11 ` Szabolcs Nagy
2015-09-24 6:35 ` Rich Felker
2015-09-23 20:34 ` Szabolcs Nagy
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