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List:       kde-bugs-dist
Subject:    [Bug 273007] New: registers messed up (--db-attach=yes related?)
From:       Pierre Habouzit <madcoder () debian ! org>
Date:       2011-05-11 6:10:20
Message-ID: bug-273007-17878 () http ! bugs ! kde ! org/
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https://bugs.kde.org/show_bug.cgi?id=273007

           Summary: registers messed up (--db-attach=yes related?)
           Product: valgrind
           Version: unspecified
          Platform: Unlisted Binaries
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: NOR
         Component: general
        AssignedTo: jseward@acm.org
        ReportedBy: madcoder@debian.org


Created an attachment (id=59891)
 --> (http://bugs.kde.org/attachment.cgi?id=59891)
zigtest.s

Here is a cut&paste from a Debian bug
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=576236), which still applies
to 3.6.1:

I've attached a .s file from a test program of unclear bugginess, which
we tried to use valgrind to check.  (It had fun and exciting strict
aliasing issues.)  In the course of debugging it, we found an error in
valgrind --db-attach=yes.

Steps to reproduce:

1) gcc zigtest.s -o zigtest
2) valgrind --db-attach=yes ./zigtest
3) When valgrind stops at an uninitialized value warning, say y to
   attach gdb.
4) "p/x $r8", which gave the value 0x30ecb1.
5) End gdb and let valgrind finish.
6) gdb ./zigtest
7) "break *0x0000000000400663"  (the address of the instruction valgrind
   stopped at)
8) "run"
9) "p/x $r8", which gave the value 0xb1.
10) Use "disas" on main to confirm that the instruction right before the
    point valgrind stopped at runs "movzbl %r8b, %r8d", which should
    zero all but the low 8 bits of %r8.  Thus, valgrind's value seems
    wrong.

- Josh Triplett

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