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[libunwind][AIX] Fix up TOC register if unw_getcontext is called from a different module #66549

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Merged
merged 2 commits into from
Sep 19, 2023
Merged

[libunwind][AIX] Fix up TOC register if unw_getcontext is called from a different module #66549

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d42f6f3
The TOC register (r2) was changed by the glue code if unw_getcontext
xingxue-ibm Sep 15, 2023
b9b6bed
Addressed comment.
xingxue-ibm Sep 18, 2023
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28 changes: 26 additions & 2 deletions libunwind/src/UnwindRegistersSave.S
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Original file line number Diff line number Diff line change
Expand Up @@ -305,9 +305,21 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
mflr 0
std 0, PPC64_OFFS_SRR0(3) // store lr as ssr0
PPC64_STR(1)
PPC64_STR(4) // Save r4 first since it will be used for fixing r2.
#if defined(_AIX)
// The TOC register (r2) was changed by the glue code if unw_getcontext
// is called from a different module. Save the original TOC register
// in the context if this is the case.
mflr 4
lwz 4, 0(4) // Get the first instruction at the return address.
xoris 0, 4, 0xe841 // Is it reloading the TOC register "ld 2,40(1)"?
cmplwi 0, 0x28
bne 0, LnoR2Fix // No need to fix up r2 if it is not.
ld 2, 40(1) // Use the saved TOC register in the stack.
LnoR2Fix:
#endif
PPC64_STR(2)
PPC64_STR(3)
PPC64_STR(4)
PPC64_STR(5)
PPC64_STR(6)
PPC64_STR(7)
Expand Down Expand Up @@ -547,9 +559,21 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
mflr 0
stw 0, 0(3) // store lr as ssr0
stw 1, 12(3)
stw 4, 24(3) // Save r4 first since it will be used for fixing r2.
#if defined(_AIX)
// The TOC register (r2) was changed by the glue code if unw_getcontext
// is called from a different module. Save the original TOC register
// in the context if this is the case.
mflr 4
lwz 4, 0(4) // Get the instruction at the return address.
xoris 0, 4, 0x8041 // Is it reloading the TOC register "ld 2,40(1)"?
cmplwi 0, 0x14
bne 0, LnoR2Fix // No need to fix up r2 if it is not.
lwz 2, 20(1) // Use the saved TOC register in the stack.
LnoR2Fix:
#endif
stw 2, 16(3)
stw 3, 20(3)
stw 4, 24(3)
stw 5, 28(3)
stw 6, 32(3)
stw 7, 36(3)
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3 changes: 0 additions & 3 deletions libunwind/test/unw_resume.pass.cpp
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Expand Up @@ -10,9 +10,6 @@
// Ensure that unw_resume() resumes execution at the stack frame identified by
// cursor.

// TODO: Investigate this failure on AIX system.
// XFAIL: target={{.*}}-aix{{.*}}

// TODO: Figure out why this fails with Memory Sanitizer.
// XFAIL: msan

Expand Down