[gnome-shell] main: call gjs_dumpstack on aborts and traps and optionally on segfaults

[Marco Trevisan <marcotrevi src gnome org>]

commit f90b225eaa99423b39d00a7fe49864e1815de90d
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Fri Oct 20 05:41:59 2017 -0500

    main: call gjs_dumpstack on aborts and traps and optionally on segfaults
    
    In order to debug issues triggered by JS code we might need to
    see the stack of it, this is not normally visible in static stack traces,
    thus we need to call gjs_dumpstack () before dying the process.
    
    Intercepting signals SIGABRT, SIGTRAP (needed for catching fatal glib
    errors) SIGFPE and SIGIOT by default, while introducing a new
    'backtrace-segfaults' flag for the SHELL_DEBUG environment variable to
    do the same on SIGSEGV and SIGBUS (this is a precaution to avoid that we
    corrupt the stack for automatic errors trackers).
    
    In any case after dumping the stack we raise the signal again, in order
    to make the system aware of it.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=789237

 src/main.c |   62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 61 insertions(+), 1 deletions(-)
---
diff --git a/src/main.c b/src/main.c
index 9a89aa4..214d2a5 100644
--- a/src/main.c
+++ b/src/main.c
@@ -38,12 +38,14 @@ extern GType gnome_shell_plugin_get_type (void);
 
 static gboolean is_gdm_mode = FALSE;
 static char *session_mode = NULL;
+static int caught_signal = 0;
 
 #define DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER 1
 #define DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER 4
 
 enum {
   SHELL_DEBUG_BACKTRACE_WARNINGS = 1,
+  SHELL_DEBUG_BACKTRACE_SEGFAULTS = 2,
 };
 static int _shell_debug;
 
@@ -290,7 +292,8 @@ static void
 shell_init_debug (const char *debug_env)
 {
   static const GDebugKey keys[] = {
-    { "backtrace-warnings", SHELL_DEBUG_BACKTRACE_WARNINGS }
+    { "backtrace-warnings", SHELL_DEBUG_BACKTRACE_WARNINGS },
+    { "backtrace-segfaults", SHELL_DEBUG_BACKTRACE_SEGFAULTS },
   };
 
   _shell_debug = g_parse_debug_string (debug_env, keys,
@@ -328,6 +331,52 @@ shut_up (const char     *domain,
 {
 }
 
+static void
+dump_gjs_stack_alarm_sigaction (int        signo,
+                                siginfo_t *info,
+                                void      *data)
+{
+  g_warning ("Failed to dump Javascript stack, got stuck");
+
+  raise (caught_signal);
+}
+
+static void
+dump_gjs_stack_on_signal_handler (int signo)
+{
+  /* Waiting at least 5 seconds for the dumpstack, if it fails, we raise the error */
+  struct sigaction sa;
+
+  caught_signal = signo;
+  memset (&sa, 0, sizeof (sigaction));
+  sigemptyset (&sa.sa_mask);
+
+  sa.sa_flags     = SA_SIGINFO;
+  sa.sa_sigaction = dump_gjs_stack_alarm_sigaction;
+
+  sigaction (SIGALRM, &sa, NULL);
+
+  alarm (5);
+  gjs_dumpstack ();
+  alarm (0);
+
+  raise (signo);
+}
+
+static void
+dump_gjs_stack_on_signal (int signo)
+{
+  struct sigaction sa;
+
+  memset (&sa, 0, sizeof (sigaction));
+  sigemptyset (&sa.sa_mask);
+
+  sa.sa_flags   = SA_RESETHAND;
+  sa.sa_handler = dump_gjs_stack_on_signal_handler;
+
+  sigaction (signo, &sa, NULL);
+}
+
 static gboolean
 list_modes (const char  *option_name,
             const char  *value,
@@ -459,6 +508,17 @@ main (int argc, char **argv)
 
   shell_prefs_init ();
 
+  dump_gjs_stack_on_signal (SIGABRT);
+  dump_gjs_stack_on_signal (SIGFPE);
+  dump_gjs_stack_on_signal (SIGIOT);
+  dump_gjs_stack_on_signal (SIGTRAP);
+
+  if ((_shell_debug & SHELL_DEBUG_BACKTRACE_SEGFAULTS))
+    {
+      dump_gjs_stack_on_signal (SIGBUS);
+      dump_gjs_stack_on_signal (SIGSEGV);
+    }
+
   ecode = meta_run ();
 
   g_debug ("Doing final cleanup");