From: Paolo Bonzini <pbonzini@redhat.com>
To: Florian Weimer <fweimer@redhat.com>, qemu-devel@nongnu.org
Cc: Eduardo Habkost <ehabkost@redhat.com>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] i386: SSE 4 implementation does not match bare metal
Date: Mon, 12 Oct 2015 11:51:55 +0200 [thread overview]
Message-ID: <561B82BB.3000609@redhat.com> (raw)
In-Reply-To: <561B6DA5.4040101@redhat.com>
On 12/10/2015 10:21, Florian Weimer wrote:
> We received a bug report that the SSE-4.2-based strstr in glibc 2.17 was
> misbehaving and returned NULL for certain inputs, even though the search
> pattern is clearly present in the subject string. I'm attaching a test
> case. You can run it as "./tst-strstr 3" to directly go to one failing
> case.
>
> I'm not sure how to debug this further, except by running the program
> under GDB, single-step through it, dump registers, and compare the
> results with a bare-metal implement after each instruction executed.
Headscratching and reading the Intel SDM is usually the best way if you
can reduce it to a single instruction (and in this case pcmpXstrX was
obviously the most likely culprit).
> Downstream bug: https://bugzilla.redhat.com/show_bug.cgi?id=1270703
> There is also an attachment with a pre-compiled binary.
Patch sent, thanks for the report.
Paolo
prev parent reply other threads:[~2015-10-12 9:52 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-12 8:21 [Qemu-devel] i386: SSE 4 implementation does not match bare metal Florian Weimer
2015-10-12 9:51 ` Paolo Bonzini [this message]
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