[libunwind] [libunwind][Haiku] Fix signal frame unwinding (PR #135367)

[via cfe-commits]

================
@@ -3032,6 +2983,162 @@ int UnwindCursor<A, R>::stepThroughSigReturn(Registers_s390x &) {
 #endif // defined(_LIBUNWIND_CHECK_LINUX_SIGRETURN) &&
        // defined(_LIBUNWIND_TARGET_S390X)
 
+#if defined(_LIBUNWIND_CHECK_HAIKU_SIGRETURN)
+
+#if defined(B_HAIKU_32_BIT)
+typedef Elf32_Sym elf_sym;
+#define ELF_ST_TYPE ELF32_ST_TYPE
+#elif defined(B_HAIKU_64_BIT)
+typedef Elf64_Sym elf_sym;
+#define ELF_ST_TYPE ELF64_ST_TYPE
+#endif
+
+// Private syscall declared as a weak symbol to prevent ABI breaks.
+extern "C" status_t __attribute__((weak))
+_kern_read_kernel_image_symbols(image_id id, elf_sym *symbolTable,
+                                int32 *_symbolCount, char *stringTable,
+                                size_t *_stringTableSize, addr_t *_imageDelta);
+
+static addr_t signalHandlerBegin = 0;
+static addr_t signalHandlerEnd = 0;
+
+template <typename A, typename R>
+bool UnwindCursor<A, R>::setInfoForSigReturn() {
+  if (signalHandlerBegin == 0) {
+    // If we do not have the addresses yet, find them now.
+
+    // Determine if the private function is there and usable.
+    if (_kern_read_kernel_image_symbols == nullptr) {
+      signalHandlerBegin = (addr_t)-1;
+      return false;
+    }
+
+    // Get the system commpage and enumerate its symbols.
+    image_id commpageImage = -1;
+    image_info info;
+    int32 cookie = 0;
+    while (get_next_image_info(B_SYSTEM_TEAM, &cookie, &info) == B_OK) {
----------------
waddlesplash wrote:

Those sound like good ideas. What APIs do other OSes provide here, is there something we can copy directly?

https://github.com/llvm/llvm-project/pull/135367