pytest: backtrace on internal errors in subdaemons.

A backtrace which makes it much easier to figure out what's happening.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/daemon.c

@@ -32,17 +32,25 @@ static int backtrace_status(void *unused UNUSED, uintptr_t pc,
 	return 0;
 }
 
-static void crashdump(int sig)
+void send_backtrace(const char *why)
 {
 	/* We do stderr first, since it's most reliable. */
-	warnx("Fatal signal %d (version %s)", sig, version());
+	warnx("%s (version %s)", why, version());
 	if (backtrace_state)
 		backtrace_print(backtrace_state, 0, stderr);
 
 	/* Now send to parent. */
-	bt_print("FATAL SIGNAL %d (version %s)", sig, version());
+	bt_print("%s (version %s)", why, version());
 	if (backtrace_state)
 		backtrace_full(backtrace_state, 0, backtrace_status, NULL, NULL);
+}
+
+static void crashdump(int sig)
+{
+	char why[100];
+
+	snprintf(why, 100, "FATAL SIGNAL %d", sig);
+	send_backtrace(why);
 
 	/* Probably shouldn't return. */
 	bt_exit();
@@ -66,6 +74,10 @@ static void crashlog_activate(void)
 	sigaction(SIGSEGV, &sa, NULL);
 	sigaction(SIGBUS, &sa, NULL);
 }
+#else
+void send_backtrace(const char *why)
+{
+}
 #endif
 
 int daemon_poll(struct pollfd *fds, nfds_t nfds, int timeout)

common/daemon.h

@@ -11,6 +11,9 @@ void daemon_setup(const char *argv0,
 /* Exposed for lightningd's use. */
 int daemon_poll(struct pollfd *fds, nfds_t nfds, int timeout);
 
+/* Print a backtrace to stderr, and via backtrace_print */
+void send_backtrace(const char *why);
+
 /* Shutdown for a valgrind-clean exit (frees everything) */
 void daemon_shutdown(void);
 

common/status.c

@@ -5,6 +5,7 @@
 #include <ccan/fdpass/fdpass.h>
 #include <ccan/read_write_all/read_write_all.h>
 #include <ccan/tal/str/str.h>
+#include <common/daemon.h>
 #include <common/daemon_conn.h>
 #include <common/gen_status_wire.h>
 #include <common/status.h>
@@ -167,6 +168,10 @@ void status_failed(enum status_failreason reason, const char *fmt, ...)
 	str = tal_vfmt(NULL, fmt, ap);
 	va_end(ap);
 
+	/* Give a nice backtrace when this happens! */
+	if (reason == STATUS_FAIL_INTERNAL_ERROR)
+		send_backtrace(str);
+
 	status_send_fatal(take(towire_status_fail(NULL, reason, str)),
 			  -1, -1);
 }