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Message-ID: <20130616194144.GS29800@brightrain.aerifal.cx>
Date: Sun, 16 Jun 2013 15:41:44 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: valgrind problems
On Sun, Jun 16, 2013 at 09:38:25PM +0200, Szabolcs Nagy wrote:
> > I'm pretty sure valgrind's failure here is not missing the fact that
> > brk (or any new anonymous pages) are zero pages; it's seeing the call
> > to a function named "malloc" and treating the memory pointed to by the
> > result as containing indeterminate values. If valgrind's logic were
> > merely considering anonymous memory from brk or mmap as indeterminate,
> > it could not catch errors due to use of indeterminate values in memory
> > obtained by malloc that was recycled from an earlier call to free.
>
> the problem only shows up with static linking
> where valgrind does not see the malloc call,
> only brk
>
> valgrind thinks that brk is uninitialized
>
> it is easy to demonstrate even with glibc
> (using static linking and valgind --track-origins=yes)
>
> so we should just let valgrind know that brk
> is ok
Oh, okay -- I misunderstood the problem then. And indeed the solution
is just to tell valgrind that new memory from brk and anonymous mmap
is zero-filled. I'm actually fairly surprised it doesn't already know
that...
Rich
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