[Unwind][AArch64] Match sigreturn instructions in big endian

[hstk30-hw]

Since insns are always stored LE, on a BE system the opcodes will be loaded byte-reversed. Therefore, define two sets of opcodes, one for LE and one for BE.

[llvmbot]

@llvm/pr-subscribers-libunwind

Author: None (hstk30-hw)

Changes

Since insns are always stored LE, on a BE system the opcodes will be loaded byte-reversed. Therefore, define two sets of opcodes, one for LE and one for BE.

---

Full diff: https://github.com/llvm/llvm-project/pull/167139.diff

1 Files Affected:

• (modified) libunwind/src/UnwindCursor.hpp (+9-1)

diff --git a/libunwind/src/UnwindCursor.hpp b/libunwind/src/UnwindCursor.hpp
index 7ec5f9e91578a..9414fd8a81525 100644
--- a/libunwind/src/UnwindCursor.hpp
+++ b/libunwind/src/UnwindCursor.hpp
@@ -58,6 +58,14 @@
 #include "RWMutex.hpp"
 #include "Unwind-EHABI.h"
 
+#if defined(__AARCH64EB__)
+#define MOVZ_X8_8B 0x681180d2
+#define SVC_0 0x010000d4
+#else
+#define MOVZ_X8_8B 0xd2801168
+#define SVC_0 0xd4000001
+#endif
+
 #if defined(_LIBUNWIND_SUPPORT_SEH_UNWIND)
 // Provide a definition for the DISPATCHER_CONTEXT struct for old (Win7 and
 // earlier) SDKs.
@@ -2827,7 +2835,7 @@ bool UnwindCursor<A, R>::setInfoForSigReturn(Registers_arm64 &) {
     return false;
   auto *instructions = reinterpret_cast<const uint32_t *>(pc);
   // Look for instructions: mov x8, #0x8b; svc #0x0
-  if (instructions[0] != 0xd2801168 || instructions[1] != 0xd4000001)
+  if (instructions[0] != MOVZ_X8_8B || instructions[1] != SVC_0)
     return false;
 
   _info = {};

[ajordanr-google]

This LGTM, and is simple enough, though I shouldn't be an authoritative reviewer on this. @rprichard hopefully can give a more proper review.

[rprichard]

Seems fine to me too.

I'm wondering to what extent libunwind can be used to unwind a non-native architecture.

[hstk30-hw]

I'm wondering to what extent libunwind can be used to unwind a non-native architecture.

This patch only affects the native architecture.
SigReturn function is wrapped by macro _LIBUNWIND_TARGET_LINUX and _LIBUNWIND_TARGET_XX,
which controled by _LIBUNWIND_IS_NATIVE_ONLY.