https://bugs.kde.org/show_bug.cgi?id=419271
Bug ID: 419271
Summary: false positives due to not recognizing vpxor as
dependency breaking idiom
Product: valgrind
Version: 3.13.0
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: memcheck
Assignee: jsew...@acm.org
Reporter: rzarz...@redhat.com
Target Milestone: ---
Following code is a variant of dependency breaking idiom:
vmovdqa %xmm0,%xmm3
vpxor %xmm0,%xmm3,%xmm3
Value of xmm3 will always be cleared but it seems Valgrind misses that
when computing the validity bits:
(gdb) info registers xmm3 xmm3s1 xmm3s2
xmm3 {... uint128 = 0x00000000000000000000000000000000}
xmm3s1 {... uint128 = 0xffffffffffffff000000000000000000}
More output from gdb on debugging `gcm_ghash_avx` of OpenSSL:
Breakpoint 2, gcm_ghash_avx () at ghash-x86_64.s:1365
1365 vzeroupper
(gdb) stepi
...
1598 vmovdqa %xmm0,%xmm3
(gdb) info registers xmm0 xmm0s1 xmm0s2
xmm0 {... uint128 = 0x0000000000b4560115ffdd21dcc25ea8}
xmm0s1 {... uint128 = 0xffffffffffffff000000000000000000}
xmm0s2 {... uint128 = 0x00000000000000000000000000000000}
(gdb) stepi
1599 vmovdqa %xmm1,%xmm4
(gdb) info registers xmm3 xmm3s1 xmm3s2
xmm3 {... uint128 = 0x0000000000b4560115ffdd21dcc25ea8}
xmm3s1 {... uint128 = 0xffffffffffffff000000000000000000}
xmm3s2 {... uint128 = 0x00000000000000000000000000000000}
(gdb) stepi
1600 vmovdqa %xmm2,%xmm5
(gdb) stepi
1601 subq $0x10,%rcx
(gdb)
1602 jz .Ltail_avx
(gdb)
1696 vpxor %xmm10,%xmm15,%xmm15
(gdb)
1698 vpunpckhqdq %xmm15,%xmm15,%xmm8
(gdb)
1699 vpxor %xmm0,%xmm3,%xmm3
(gdb) stepi
1700 vpclmulqdq $0x00,%xmm6,%xmm15,%xmm0
(gdb) info registers xmm0 xmm0s1 xmm0s2
xmm0 {... uint128 = 0x0000000000b4560115ffdd21dcc25ea8}
xmm0s1 {... uint128 = 0xffffffffffffff000000000000000000}
xmm0s2 {... uint128 = 0x00000000000000000000000000000000}
(gdb) info registers xmm3 xmm3s1 xmm3s2
xmm3 {... uint128 = 0x00000000000000000000000000000000}
xmm3s1 {... uint128 = 0xffffffffffffff000000000000000000}
xmm3s2 {... uint128 = 0x00000000000000000000000000000000}
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