Bug#645592: libc6: 2.11 (maybe?) breaks backwards (binary) compatibility
On Mon, Oct 17, 2011 at 10:43:57AM +0200, Aurelien Jarno wrote:
> On Mon, Oct 17, 2011 at 10:03:44AM +0200, Lionel Elie Mamane wrote:
>> Package: libc6
>> Version: 2.11.1-1
>> Severity: important
>> On amd64, one specific program behaves differently when run with
>> libc6 2.10.2-9 (or earlier) than when run with libc6 2.11.1-1 (or
>> later).
>> (..) it looks like a 2.10 vs 2.11 thing. I vaguely looked at the NEWS file and diff of source code between those versions, the only thing that struck my eye is:
>> * New optimized string functions for x86-64: strstr, strcasestr, memcmp,
>> strcspn, strpbrk, strspn, strcpy, stpcpy, strncpy, strcmp (SSE2, SSE4.2),
>> strncmp (SSE2, SSE4.2), strchr (SSE4.2), strrchr (SSE4.2).
>> Contributed by H.J. Lu.
>> strlen, rawmemchr, strcmp (SSSE3), strncmp (SSSE3).
>> Implemented by Ulrich Drepper.
>> But I think that if these functions were buggy, we would have noticed!
>> So, unlikely.
> This is likely to be these functions actually, and more precisely
> memcpy(). C standards specifies that the source and dest areas
> should not overlap, otherwise memmove() should be used
> instead. Recent version of the libc uses to optimize this function,
> but some binaries use memcpy() while they should use memmove().
> Given your code is closed source and thus can't be fixed, the best
> is to use the provided wrapper, see
> /usr/share/doc/libc6/NEWS.Debian.gz for more information about how
> to use them.
Interesting theory, but according the NEWS.Debian.gz of *sid* and the
BTS entries linked to, the issue you refer to seems to be new to
(e)glibc 2.13, not (e)glibc 2.11... And the problem was originally
observed in *squeeze*. And I've just checked for overlap by running
these on the latrace output:
grep ' memcpy(' | sed 's/[(,)]/ /g' | gawk '{if ( strtonum($8) <= strtonum($5) && strtonum($8) + strtonum($11) >= strtonum($5)) print "overlap: " $5 " " $8 " " $11 }'
grep ' memcpy(' | sed 's/[(,)]/ /g' | gawk '{if ( strtonum($8) >= strtonum($5) && strtonum($5) + strtonum($11) >= strtonum($8)) print "overlap: " $5 " " $8 " " $11 }'
Do you happen to have another theory, that would apply to a change
between 2.10 and 2.11?
--
Lionel
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