gh-96055: Update faulthandler to emit proper unexpect signal name

Author: corona10

Misc/NEWS.d/next/Core and Builtins/2022-11-06-22-59-02.gh-issue-96055.TmQuJn.rst

@@ -0,0 +1,2 @@
+Update :mod:`faulthandler` to emit an error message with the proper
+unexpected signal name. Patch by Dong-hee Na.

Modules/faulthandler.c

@@ -6,7 +6,7 @@
 #include "pycore_traceback.h"     // _Py_DumpTracebackThreads
 
 #include <object.h>
-#include <signal.h>
+#include <signal.h>               // sys_signame
 #include <stdlib.h>               // abort()
 #if defined(HAVE_PTHREAD_SIGMASK) && !defined(HAVE_BROKEN_PTHREAD_SIGMASK) && defined(HAVE_PTHREAD_H)
 #  include <pthread.h>
@@ -333,14 +333,17 @@ faulthandler_fatal_error(int signum)
     size_t i;
     fault_handler_t *handler = NULL;
     int save_errno = errno;
+    int found = 0;
 
     if (!fatal_error.enabled)
         return;
 
     for (i=0; i < faulthandler_nsignals; i++) {
         handler = &faulthandler_handlers[i];
-        if (handler->signum == signum)
+        if (handler->signum == signum) {
+            found = 1;
             break;
+        }
     }
     if (handler == NULL) {
         /* faulthandler_nsignals == 0 (unlikely) */
@@ -350,9 +353,16 @@ faulthandler_fatal_error(int signum)
     /* restore the previous handler */
     faulthandler_disable_fatal_handler(handler);
 
-    PUTS(fd, "Fatal Python error: ");
-    PUTS(fd, handler->name);
-    PUTS(fd, "\n\n");
+    if (found) {
+        PUTS(fd, "Fatal Python error: ");
+        PUTS(fd, handler->name);
+        PUTS(fd, "\n\n");
+    }
+    else {
+        PUTS(fd, "Fatal Python error from unexpected signal: ");
+        PUTS(fd, strdup(sys_signame[signum]));
+        PUTS(fd, "\n\n");
+    }
 
     faulthandler_dump_traceback(fd, fatal_error.all_threads,
                                 fatal_error.interp);