From: Segher Boessenkool <segher@kernel•crashing.org>
To: William Kennington <wak@google•com>
Cc: linuxppc-dev@lists•ozlabs.org
Subject: Re: GCC strcmp optimizations causing valgrind uninitialized conditional jumps
Date: Tue, 3 Jul 2018 14:18:33 -0500 [thread overview]
Message-ID: <20180703191833.GG16221@gate.crashing.org> (raw)
In-Reply-To: <CAPnigK=HP_F6a3EuM-G8XHH1G_SyLCscT72=yVwtFxDmBZ6WOQ@mail.gmail.com>
On Tue, Jul 03, 2018 at 11:59:14AM -0700, William Kennington wrote:
> Is there a bug tracking the issue?
https://bugs.kde.org/show_bug.cgi?id=386945
> Also, unless your malloc is
> guaranteed to be zeroing out the data or have a strcmp that is writing
> doubleworld aligned data to the string, the strcmp implementation is
> branching based on data existing after the null terminating character
> that may be uninitialized. Both sides of the branch do the right thing
> though, and locate the null terminator, throwing away the calculations
> done on the uninitialized data.
Yes, there is one branch that depends in part on irrelevant data, but
that is handled immediately afterwards.
> -fno-builtin-strcmp or -mstring-compare-inline-limit=0 do work fine
> but we don't control the binaries we are linking against in all cases
> and are seeing the issue pop up there.
Yeah, nasty. I don't know what to do then (other than fix valgrind, which
isn't so easy either though!)
Segher
prev parent reply other threads:[~2018-07-03 19:18 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-03 18:26 GCC strcmp optimizations causing valgrind uninitialized conditional jumps William Kennington
2018-07-03 18:46 ` Segher Boessenkool
2018-07-03 18:59 ` William Kennington
2018-07-03 19:18 ` Segher Boessenkool [this message]
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