logging/diag: Enable stacktrace diagnostic if config'd

This commit adds a signal handler for SIGSEGV when configured. The
signal handler emits a one line stack trace using SCLogError. The intent
is to provide diagnostic information in deployments where core files are
not possible.

The diagnostic message is from the offending thread and includes the
stack trace; each frame includes the symbol + offset.

src/suricata.c

@@ -298,6 +298,53 @@ static void SignalHandlerSigterm(/*@unused@*/ int sig)
 {
     sigterm_count = 1;
 }
+#ifndef OS_WIN32
+#if HAVE_LIBUNWIND
+#define UNW_LOCAL_ONLY
+#include <libunwind.h>
+static void SignalHandlerUnexpected(int sig_num, siginfo_t *info, void *context)
+{
+    char msg[SC_LOG_MAX_LOG_MSG_LEN];
+    unw_cursor_t cursor;
+    int r;
+    if ((r = unw_init_local(&cursor, (unw_context_t *)(context)) != 0)) {
+        fprintf(stderr, "unable to obtain stack trace: unw_init_local: %s\n", unw_strerror(r));
+        goto terminate;
+    }
+
+    char *temp = msg;
+    int cw = snprintf(temp, SC_LOG_MAX_LOG_MSG_LEN - (temp - msg), "stacktrace:sig %d:", sig_num);
+    temp += cw;
+    r = 1;
+    while (r > 0) {
+        if (unw_is_signal_frame(&cursor) == 0) {
+            unw_word_t off;
+            char name[256];
+            if (unw_get_proc_name(&cursor, name, sizeof(name), &off) == UNW_ENOMEM) {
+                cw = snprintf(temp, SC_LOG_MAX_LOG_MSG_LEN - (temp - msg), "[unknown]:");
+            } else {
+                cw = snprintf(
+                        temp, SC_LOG_MAX_LOG_MSG_LEN - (temp - msg), "%s+0x%08" PRIx64, name, off);
+            }
+            temp += cw;
+        }
+
+        r = unw_step(&cursor);
+        if (r > 0) {
+            cw = snprintf(temp, SC_LOG_MAX_LOG_MSG_LEN - (temp - msg), ";");
+            temp += cw;
+        }
+    }
+    SCLogError(SC_ERR_SIGNAL, "%s", msg);
+
+terminate:
+    // Terminate with SIGABRT ... but first, restore that signal's default handling
+    signal(SIGABRT, SIG_DFL);
+    abort();
+}
+#undef UNW_LOCAL_ONLY
+#endif /* HAVE_LIBUNWIND */
+#endif /* !OS_WIN32 */
 #endif
 
 #ifndef OS_WIN32
@@ -2005,6 +2052,22 @@ static int InitSignalHandler(SCInstance *suri)
 #ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
     UtilSignalHandlerSetup(SIGINT, SignalHandlerSigint);
     UtilSignalHandlerSetup(SIGTERM, SignalHandlerSigterm);
+#if HAVE_LIBUNWIND
+    int enabled;
+    if (ConfGetBool("logging.stacktrace-on-signal", &enabled) == 0) {
+        enabled = 1;
+    }
+
+    if (enabled) {
+        SCLogInfo("Preparing unexpected signal handling");
+        struct sigaction stacktrace_action;
+        memset(&stacktrace_action, 0, sizeof(stacktrace_action));
+        stacktrace_action.sa_sigaction = SignalHandlerUnexpected;
+        stacktrace_action.sa_flags = SA_SIGINFO;
+        sigaction(SIGSEGV, &stacktrace_action, NULL);
+        sigaction(SIGABRT, &stacktrace_action, NULL);
+    }
+#endif /* HAVE_LIBUNWIND */
 #endif
 #ifndef OS_WIN32
     UtilSignalHandlerSetup(SIGHUP, SignalHandlerSigHup);