[libunwind] [libunwind] Unwind through AArch64 FreeBSD signal trampolines (PR #235065)

[via cfe-commits]

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@@ -3329,6 +3344,65 @@ int UnwindCursor<A, R>::stepThroughSigReturn(Registers_s390x &) {
 #endif // defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN) &&
        // defined(_LIBUNWIND_TARGET_S390X)
 
+#if defined(_LIBUNWIND_CHECK_FREEBSD_SIGRETURN)
+template <typename A, typename R>
+bool UnwindCursor<A, R>::setInfoForSigReturn() {
+  // Ask the kernel rather than reading instructions at a possibly invalid PC.
+  // This is only used when no unwind information was found. Keep the result
+  // local to avoid shared mutable state when unwinding from a signal handler.
+  struct kinfo_sigtramp kst = {};
+  size_t len = sizeof(kst);
+  int mib[] = {CTL_KERN, KERN_PROC, KERN_PROC_SIGTRAMP, getpid()};
+  const int savedErrno = errno;
+  const int result = sysctl(mib, 4, &kst, &len, nullptr, 0);
+  errno = savedErrno;
+  if (result != 0)
+    return false;
+
+  const pint_t pc = static_cast<pint_t>(this->getReg(UNW_REG_IP));
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aokblast wrote:

Oh. I miss this. They do this by vdso. It makes sense now.

https://github.com/llvm/llvm-project/pull/235065