libunwind: Implement the unw_strerror function for better nongnu libunwind compatibility (llvm#160887)

As it was explained to me in
https://discourse.llvm.org/t/libunwinds-raison-detre/88283/2 the LLVM
version of libunwind is mostly compatible with nongnu one. This change
improves the compatibility a bit further.

Author: arrowd

libunwind/include/libunwind.h

@@ -234,6 +234,7 @@ extern int unw_is_fpreg(unw_cursor_t *, unw_regnum_t) LIBUNWIND_AVAIL;
 extern int unw_is_signal_frame(unw_cursor_t *) LIBUNWIND_AVAIL;
 extern int unw_get_proc_name(unw_cursor_t *, char *, size_t, unw_word_t *) LIBUNWIND_AVAIL;
 //extern int       unw_get_save_loc(unw_cursor_t*, int, unw_save_loc_t*);
+extern const char *unw_strerror(int) LIBUNWIND_AVAIL;
 
 extern unw_addr_space_t unw_local_addr_space;
 

libunwind/src/libunwind.cpp

@@ -409,6 +409,41 @@ void __unw_remove_dynamic_eh_frame_section(unw_word_t eh_frame_start) {
 }
 
 #endif // defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
+
+/// Maps the UNW_* error code to a textual representation
+_LIBUNWIND_HIDDEN const char *__unw_strerror(int error_code) {
+  switch (error_code) {
+  case UNW_ESUCCESS:
+    return "no error";
+  case UNW_EUNSPEC:
+    return "unspecified (general) error";
+  case UNW_ENOMEM:
+    return "out of memory";
+  case UNW_EBADREG:
+    return "bad register number";
+  case UNW_EREADONLYREG:
+    return "attempt to write read-only register";
+  case UNW_ESTOPUNWIND:
+    return "stop unwinding";
+  case UNW_EINVALIDIP:
+    return "invalid IP";
+  case UNW_EBADFRAME:
+    return "bad frame";
+  case UNW_EINVAL:
+    return "unsupported operation or bad value";
+  case UNW_EBADVERSION:
+    return "unwind info has unsupported version";
+  case UNW_ENOINFO:
+    return "no unwind info found";
+#if defined(_LIBUNWIND_TARGET_AARCH64) && !defined(_LIBUNWIND_IS_NATIVE_ONLY)
+  case UNW_ECROSSRASIGNING:
+    return "cross unwind with return address signing";
+#endif
+  }
+  return "invalid error code";
+}
+_LIBUNWIND_WEAK_ALIAS(__unw_strerror, unw_strerror)
+
 #endif // !defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__wasm__)
 
 #ifdef __APPLE__

libunwind/src/libunwind_ext.h

@@ -46,6 +46,7 @@ extern int __unw_get_proc_info(unw_cursor_t *, unw_proc_info_t *);
 extern int __unw_is_fpreg(unw_cursor_t *, unw_regnum_t);
 extern int __unw_is_signal_frame(unw_cursor_t *);
 extern int __unw_get_proc_name(unw_cursor_t *, char *, size_t, unw_word_t *);
+extern const char *__unw_strerror(int);
 
 #if defined(_AIX)
 extern uintptr_t __unw_get_data_rel_base(unw_cursor_t *);