https://bugs.kde.org/show_bug.cgi?id=454040
Bug ID: 454040
Summary: s390x: False-positive memcheck:cond in memmem on
arch13 systems
Product: valgrind
Version: unspecified
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: ar...@linux.ibm.com
Target Milestone: ---
On a system that supports the vector enhancements facility 2 (arch13 or
higher), glibc runs an optimized version of memmem that uses the "vector string
search" instruction. That implementation contains a conditional jump that may
depend on undefined values; however, the end result of the function is still
independent from these undefined values. Since memcheck can't see that, it may
report a false positive, as reproduced like this:
$ valgrind perl -e "use lib '.'; require BarXXXXXXXXXXXXXXX;"
...
==3271940== Conditional jump or move depends on uninitialised value(s)
==3271940== at 0x4CAABB6: __memmem_arch13 (memmem-arch13.S:65)
==3271940== by 0x49B64FF: Perl_pp_require (in
/usr/lib64/libperl.so.5.32.1)
==3271940== by 0x49654C1: Perl_runops_standard (in
/usr/lib64/libperl.so.5.32.1)
==3271940== by 0x48DC3F5: perl_run (in /usr/lib64/libperl.so.5.32.1)
==3271940== by 0x108E37: main (in /usr/bin/perl)
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