Re: [PATCH] valgrind: ignore SSE-based strlen invalid reads
On mié, 2011-03-16 at 13:18 -0700, Junio C Hamano wrote:
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> Carlos Martín Nieto <cmn@elego.de> writes:
>
> > Some versions of strlen use SSE to speed up the calculation and load 4
> > bytes at a time, even if it means reading past the end of the
> > allocated memory. This read is safe and when the strlen function is
> > inlined, it is not replaced by valgrind, which reports a
> > false-possitive.
> >
> > Tell valgrind to ignore this particular error, as the read is, in
> > fact, safe. Current upstream-released version 2.6.1 is affected. Some
> > distributions have this fixed in their latest versions.
> >
> > Signed-off-by: Carlos Martín Nieto <cmn@elego.de>
> > ---
> >
> >>> I think 3.6.1 doesn't need it, as Debian's 1:3.5.0+3.6.0svn20100609-1
> >>> version is reportedly fixed.
> >>
> >>Ah, nice. A phrase like "some versions of valgrind before 3.6.1"
> >>would be fine with me fwiw. :)
> >
> > I just downloaded and compiled the upstream release 2.6.1 and it's
> > still affected (it does fix some other related
> > false-positives). Fedorea rawhide has the fix in, according to their
> > bug tracker. I haven't tested the reportedly-fixed version in Debian
> > yet.
>
> I take it that you meant 3.6.1 in both places above?
>
Yeah, I blame the kernel ;)
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> This somehow reminds me of my past life where I saw a buggy implementation
> of strlen() in the C library loaded one word too many from memory, and
> segfaulted even when the string ended before the end of a mapped page when
> the next page was unmapped.
>
> Anyway, nice digging.
If all else fails, google will point you to the bug tracker :)
Carlos Martín Nieto <cmn@elego.de>