[libunwind] fix unwinding from signal handler

[azat]

In case of this is frame of signal handler, the IP should be incremented, because the IP saved in the signal handler points to first non-executed instruction, while FDE/CIE expects IP to be after the first non-executed instruction.

Refs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26208

[llvmbot]

@llvm/pr-subscribers-libunwind

Author: Azat Khuzhin (azat)

Changes

In case of this is frame of signal handler, the IP should be incremented, because the IP saved in the signal handler points to first non-executed instruction, while FDE/CIE expects IP to be after the first non-executed instruction.

Refs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26208

---

Full diff: https://github.com/llvm/llvm-project/pull/92291.diff

1 Files Affected:

• (modified) libunwind/src/DwarfInstructions.hpp (+6-1)

diff --git a/libunwind/src/DwarfInstructions.hpp b/libunwind/src/DwarfInstructions.hpp
index bd9ece60ee588..5ea535be4b974 100644
--- a/libunwind/src/DwarfInstructions.hpp
+++ b/libunwind/src/DwarfInstructions.hpp
@@ -365,7 +365,12 @@ int DwarfInstructions<A, R>::stepWithDwarf(A &addressSpace, pint_t pc,
 
       // Return address is address after call site instruction, so setting IP to
       // that does simulates a return.
-      newRegisters.setIP(returnAddress);
+      //
+      // In case of this is frame of signal handler, the IP should be
+      // incremented, because the IP saved in the signal handler points to
+      // first non-executed instruction, while FDE/CIE expects IP to be after
+      // the first non-executed instruction.
+      newRegisters.setIP(returnAddress + cieInfo.isSignalFrame);
 
       // Simulate the step by replacing the register set with the new ones.
       registers = newRegisters;

[azat]

Build and Test libc++ / stage3 (generic-ubsan, libcxx-runners-8-set) (pull_request) Failing after 10m

Looks like unrelated?

2024-05-15T17:48:22.3468783Z ##[error]The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

[azat]

Can someone take a look? Maybe @MaskRay @compnerd (according to the most frequent reviewers from Reviewed By tag)

[compnerd]

Thanks, this seems like the right place to handle this.

[compnerd]

@azat do you need this to be committed on your behalf?

[azat]

@azat do you need this to be committed on your behalf?

I would be very much appreciate that, since I don't have write access.

[ldionne]

Is it possible to add a test case for this?

[daltenty]

This is breaking a number of tests for the UBSAN on AIX, the traceback produced by the runtime are no longer correct.

Before this change:

UndefinedBehaviorSanitizer:DEADLYSIGNAL
==52887862==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address 0x00000000 (pc 0x10000784 bp 0x2ff22020 sp 0x2ff22020 T59639729)
==52887862==The signal is caused by a UNKNOWN memory access.
==52887862==Hint: address points to the zero page.
    #0 0x10000784 in .void Xyz::Abc<int, int>() /home/daltenty/llvm/dev/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/dedup_token_length_test.cpp:20
    #1 0x1000073c in .bar /home/daltenty/llvm/dev/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/dedup_token_length_test.cpp:25
    #2 0x100007cc in .FOO() /home/daltenty/llvm/dev/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/dedup_token_length_test.cpp:29
    #3 0x10000834 in .main /home/daltenty/llvm/dev/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/dedup_token_length_test.cpp:33
    #4 0x100002d0 in .__start (/home/daltenty/llvm/dev/build/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/ubsan-powerpc-AIX/Posix/Output/dedup_token_length_test.cpp.tmp+0x100002d0)

DEDUP_TOKEN: .void Xyz::Abc<int, int>()--.bar
UndefinedBehaviorSanitizer can not provide additional info.
SUMMARY: UndefinedBehaviorSanitizer: SEGV /home/daltenty/llvm/dev/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/dedup_token_length_test.cpp:20 in .void Xyz::Abc<int, int>()
==52887862==ABORTING

After:

UndefinedBehaviorSanitizer:DEADLYSIGNAL
==1704572==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address 0x00000000 (pc 0x10000784 bp 0x2ff221b0 sp 0x2ff221b0 T56035233)
==1704572==The signal is caused by a UNKNOWN memory access.
==1704572==Hint: address points to the zero page.
    #0 0x10000784 in .void Xyz::Abc<int, int>() /home/daltenty/llvm/dev/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/dedup_token_length_test.cpp:20
    #1 0x1001d764 in .ubsan_GetStackTrace(__sanitizer::BufferedStackTrace*, unsigned int, unsigned int, unsigned int, void*, bool) /home/daltenty/llvm/dev/llvm-project/compiler-rt/lib/ubsan/ubsan_diag.cpp:41
    #2 0x10025ca4 in .__ubsan::OnStackUnwind(__sanitizer::SignalContext const&, void const*, __sanitizer::BufferedStackTrace*) /home/daltenty/llvm/dev/llvm-project/compiler-rt/lib/ubsan/ubsan_signals_standalone.cpp:53
    #3 0x1001cd10 in ReportDeadlySignalImpl /home/daltenty/llvm/dev/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_report.cpp:272
    #4 0x1001cd10 in .__sanitizer::ReportDeadlySignal(__sanitizer::SignalContext const&, unsigned int, void (*)(__sanitizer::SignalContext const&, void const*, __sanitizer::BufferedStackTrace*), void const*) /home/daltenty/llvm/dev/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_report.cpp:286
    #5 0x1001d2d4 in .__sanitizer::HandleDeadlySignal(void*, void*, unsigned int, void (*)(__sanitizer::SignalContext const&, void const*, __sanitizer::BufferedStackTrace*), void const*) /home/daltenty/llvm/dev/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_report.cpp:295

DEDUP_TOKEN: .void Xyz::Abc<int, int>()--.ubsan_GetStackTrace(__sanitizer::BufferedStackTrace*, unsigned int, unsigned int, unsigned int, void*, bool)
UndefinedBehaviorSanitizer can not provide additional info.
SUMMARY: UndefinedBehaviorSanitizer: SEGV /home/daltenty/llvm/dev/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/dedup_token_length_test.cpp:20 in .void Xyz::Abc<int, int>()
==1704572==ABORTING