https://bugs.kde.org/show_bug.cgi?id=502324
Bug ID: 502324
Summary: s390x: Memcheck false positives with TMxx and TM/TMY
Classification: Developer tools
Product: valgrind
Version: unspecified
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: vex
Assignee: jsew...@acm.org
Reporter: ar...@linux.ibm.com
Target Milestone: ---
It has been observed that memcheck reports false positives on s390x when a
partially undefined value is tested with one of the TMLL, TMLH, TMHL, or TMHH
instructions. These instructions test an operand against a given mask. Zero
mask bits indicate that the corresponding bits in the operand shall be "don't
care". But memcheck complains anyway if one of these bits is undefined and the
resulting condition code is used outside the current block.
One example how this may happen is like this:
tmll %r5,0x0080 # condition code is generated
mvc ... # new block, since mvc results in a loop
jne 1f # condition code is used
Let's assume that only the lowest byte of %r5 was initialized. This would be
perfectly fine for the result of tmll, but memcheck would still complain.
Essentially the same issue exists with TM and TMY.
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