GNU bug report logs - #8410
make_invisible_cursor returns garbage if XCreateBitmapFromData fails

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: bug-gnu-emacs <at> gnu.org
Subject: make_invisible_cursor returns garbage if XCreateBitmapFromData fails
Date: Fri, 01 Apr 2011 19:21:34 -0700

I found this bug via static analysis, using GCC 4.6.0's warnings.
src/xfns.c's make_invisible_cursor returns a garbage value if
XCreateBitmapFromData fails.  I plan to fix it as follows.
I don't know that returning 0 fixes the bug, so I'd like someone
who's expert in this area to look at this.  Since the patch replaces
undefined behavior with defined behavior it isn't likely to be
introducing a bug, so it shouldn't hurt to install the patch.

* xfns.c (make_invisible_cursor): Don't return garbage
if XCreateBitmapFromData fails.
=== modified file 'src/xfns.c'
--- src/xfns.c	2011-04-01 20:30:45 +0000
+++ src/xfns.c	2011-04-01 23:01:33 +0000
@@ -855,19 +855,20 @@
   static char const no_data[] = { 0 };
   Pixmap pix;
   XColor col;
-  Cursor c;
+  Cursor c = 0;

   x_catch_errors (dpy);
   pix = XCreateBitmapFromData (dpy, FRAME_X_DISPLAY_INFO (f)->root_window,
                                no_data, 1, 1);
   if (! x_had_errors_p (dpy) && pix != None)
     {
+      Cursor pixc;
       col.pixel = 0;
       col.red = col.green = col.blue = 0;
       col.flags = DoRed | DoGreen | DoBlue;
-      c = XCreatePixmapCursor (dpy, pix, pix, &col, &col, 0, 0);
-      if (x_had_errors_p (dpy) || c == None)
-        c = 0;
+      pixc = XCreatePixmapCursor (dpy, pix, pix, &col, &col, 0, 0);
+      if (! x_had_errors_p (dpy) && pixc != None)
+        c = pixc;
       XFreePixmap (dpy, pix);
     }

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