Replace exit with backtrace in crash dialog

When the user hits 'b', attach gdb and dump a backtrace to the tmpdir

src/sighandler.c

@@ -16,11 +16,14 @@
 #include <ev.h>
 #include <iconv.h>
 #include <signal.h>
+#include <sys/wait.h>
 
 #include <xcb/xcb_event.h>
 
 #include <X11/keysym.h>
 
+static void open_popups(void);
+
 static xcb_gcontext_t pixmap_gc;
 static xcb_pixmap_t pixmap;
 static int raised_signal;
@@ -29,11 +32,84 @@ static char *crash_text[] = {
     "i3 just crashed.",
     "To debug this problem, either attach gdb now",
     "or press",
-    "- 'e' to exit and get a core-dump,",
+    "- 'b' to save a backtrace (needs GDB),",
     "- 'r' to restart i3 in-place or",
     "- 'f' to forget the current layout and restart"
 };
 static int crash_text_longest = 5;
+static int backtrace_string_index = 3;
+static int backtrace_done = 0;
+
+/*
+ * Attach gdb to pid_parent and dump a backtrace to i3-backtrace.$pid in the
+ * tmpdir
+ */
+static int backtrace(void) {
+    char *tmpdir = getenv("TMPDIR");
+    if (tmpdir == NULL)
+        tmpdir = "/tmp";
+
+    pid_t pid_parent = getpid();
+
+    char *filename = NULL;
+    if (sasprintf(&filename, "%s/i3-backtrace.%d.txt", tmpdir, pid_parent) == -1
+            || filename == NULL)
+        filename = "i3-backtrace.txt";
+
+    pid_t pid_gdb = fork();
+    if (pid_gdb < 0) {
+        DLOG("Failed to fork for GDB\n");
+        return -1;
+    } else if (pid_gdb == 0) {
+        /* child */
+
+        /* close standard streams in case i3 is started from a terminal; gdb
+         * needs to run without controlling terminal for it to work properly in
+         * this situation */
+        close(STDIN_FILENO);
+        close(STDOUT_FILENO);
+        close(STDERR_FILENO);
+
+        char *pid_s = NULL;
+        sasprintf(&pid_s, "%d", pid_parent);
+
+        char *gdb_log_cmd = NULL;
+        if (sasprintf(&gdb_log_cmd, "set logging file %s", filename) == -1
+                || gdb_log_cmd == NULL)
+            gdb_log_cmd = "set logging file i3-backtrace.txt";
+
+        char *args[] = {
+            "gdb",
+            start_argv[0],
+            "-p",
+            pid_s,
+            "-batch",
+            "-nx",
+            "-ex", gdb_log_cmd,
+            "-ex", "set logging on",
+            "-ex", "bt full",
+            "-ex", "quit",
+            NULL
+        };
+        execvp(args[0], args);
+        DLOG("Failed to exec GDB\n");
+        exit(1);
+    }
+    int status = 0;
+    struct stat bt;
+
+    waitpid(pid_gdb, &status, 0);
+
+    /* see if the backtrace was succesful or not */
+    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+        DLOG("GDB did not run properly\n");
+        return -1;
+    } else if (stat(filename, &bt) == -1) {
+        DLOG("GDB executed succesfully, but no backtrace was generated\n");
+        return -1;
+    }
+    return 1;
+}
 
 /*
  * Draw the window containing the info text
@@ -51,9 +127,23 @@ static int sig_draw_window(xcb_window_t win, int width, int height, int font_hei
     /* restore font color */
     set_font_colors(pixmap_gc, get_colorpixel("#FFFFFF"), get_colorpixel("#000000"));
 
+    char *bt_colour = "#FFFFFF";
+    if (backtrace_done < 0)
+        bt_colour = "#AA0000";
+    else if (backtrace_done > 0)
+        bt_colour = "#00AA00";
+
     for (int i = 0; crash_text_i3strings[i] != NULL; ++i) {
+        /* fix the colour for the backtrace line when it finished */
+        if (i == backtrace_string_index)
+            set_font_colors(pixmap_gc, get_colorpixel(bt_colour), get_colorpixel("#000000"));
+
         draw_text(crash_text_i3strings[i], pixmap, pixmap_gc,
                 8, 5 + i * font_height, width - 16);
+
+        /* and reset the colour again for other lines */
+        if (i == backtrace_string_index)
+            set_font_colors(pixmap_gc, get_colorpixel("#FFFFFF"), get_colorpixel("#000000"));
     }
 
     /* Copy the contents of the pixmap to the real window */
@@ -64,7 +154,7 @@ static int sig_draw_window(xcb_window_t win, int width, int height, int font_hei
 }
 
 /*
- * Handles keypresses of 'e' or 'r' to exit or restart i3
+ * Handles keypresses of 'b', 'r' and 'f' to get a backtrace or restart i3
  *
  */
 static int sig_handle_key_press(void *ignored, xcb_connection_t *conn, xcb_key_press_event_t *event) {
@@ -77,10 +167,15 @@ static int sig_handle_key_press(void *ignored, xcb_connection_t *conn, xcb_key_p
 
     xcb_keysym_t sym = xcb_key_press_lookup_keysym(keysyms, event, state);
 
-    if (sym == 'e') {
+    if (sym == 'b') {
-        DLOG("User issued exit-command, raising error again.\n");
+        DLOG("User issued core-dump command.\n");
-        raise(raised_signal);
+
-        exit(1);
+        /* fork and exec/attach GDB to the parent to get a backtrace in the
+         * tmpdir */
+        backtrace_done = backtrace();
+
+        /* re-open the windows to indicate that it's finished */
+        open_popups();
     }
 
     if (sym == 'r')
@@ -129,20 +224,7 @@ static xcb_window_t open_input_window(xcb_connection_t *conn, Rect screen_rect,
     return win;
 }
 
-/*
+static void open_popups() {
- * Handle signals
- * It creates a window asking the user to restart in-place
- * or exit to generate a core dump
- *
- */
-void handle_signal(int sig, siginfo_t *info, void *data) {
-    DLOG("i3 crashed. SIG: %d\n", sig);
-
-    struct sigaction action;
-    action.sa_handler = SIG_DFL;
-    sigaction(sig, &action, NULL);
-    raised_signal = sig;
-
     /* width and height of the popup window, so that the text fits in */
     int crash_text_num = sizeof(crash_text) / sizeof(char*);
     int height = 13 + (crash_text_num * config.font.height);
@@ -182,6 +264,23 @@ void handle_signal(int sig, siginfo_t *info, void *data) {
         sig_draw_window(win, width, height, config.font.height, crash_text_i3strings);
         xcb_flush(conn);
     }
+}
+
+/*
+ * Handle signals
+ * It creates a window asking the user to restart in-place
+ * or exit to generate a core dump
+ *
+ */
+void handle_signal(int sig, siginfo_t *info, void *data) {
+    DLOG("i3 crashed. SIG: %d\n", sig);
+
+    struct sigaction action;
+    action.sa_handler = SIG_DFL;
+    sigaction(sig, &action, NULL);
+    raised_signal = sig;
+
+    open_popups();
 
     xcb_generic_event_t *event;
     /* Yay, more own eventhandlers… */