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Bug 602

Summary: SDL based apps crash when run remotely from sparc64 and being dispayed on a i386 system
Product: SDL Reporter: Brad Smith <brad>
Component: videoAssignee: Ryan C. Gordon <icculus>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: major    
Priority: P2    
Version: 1.2.13   
Hardware: x86   
OS: OpenBSD   

Description Brad Smith 2008-07-05 18:00:19 UTC 
Trying to run SDL based apps on a sparc64 system and having the display output targeted towards a i386 system results in the apps crashing. The handful of apps I have tried all crash in the same function in the SDL library.

#0  0x000000004ab475b4 in SDL_XF86VidModeGetModeLine ()
   from /usr/local/lib/libSDL.so.8.0
#1  0x000000004ab3a630 in save_mode () from /usr/local/lib/libSDL.so.8.0
#2  0x000000004ab3bccc in X11_GetVideoModes () from /usr/local/lib/libSDL.so.8.0
#3  0x000000004ab3dd18 in X11_VideoInit () from /usr/local/lib/libSDL.so.8.0
#4  0x000000004ab2efe4 in SDL_VideoInit () from /usr/local/lib/libSDL.so.8.0
#5  0x000000004ab07890 in SDL_InitSubSystem () from /usr/local/lib/libSDL.so.8.0
#6  0x000000004ab078d4 in SDL_Init () from /usr/local/lib/libSDL.so.8.0
#7  0x0000000000108328 in ?? ()
#8  0x0000000000108328 in ?? ()
Comment 1 Blue Swirl 2008-09-03 09:20:13 UTC 
I fixed this with the following patch (sorry, the attachment thing doesn't work):
--- src/video/Xext/Xxf86vm/XF86VMode.c.orig     Mon Dec 31 04:48:09 2007
+++ src/video/Xext/Xxf86vm/XF86VMode.c  Fri Aug 22 18:59:44 2008
@@ -281,7 +281,8 @@
        }
        _XRead(dpy, (char*)modeline->private, modeline->privsize * sizeof(INT32));
     } else {
-       modeline->private = NULL;
+       // Avoid unaligned trap on Sparc64
+       memset(&modeline->private, '\0', sizeof(modeline->private));
     }
     UnlockDisplay(dpy);
     SyncHandle();
Comment 2 Brad Smith 2008-09-03 13:13:27 UTC 
> I fixed this with the following patch

As we had talked about in private I tried out your diff and SDL is still crashing. I double checked and rebuilt the library just to make sure and indeed it is still crashing.
Comment 3 Blue Swirl 2008-09-07 05:13:41 UTC 
(In reply to comment #2)
> > I fixed this with the following patch
> 
> As we had talked about in private I tried out your diff and SDL is still
> crashing. I double checked and rebuilt the library just to make sure and indeed
> it is still crashing.
> 

Sorry, I had changed the compiler flags from -O2 to -g, and with -O2 level gcc optimizes the memset back to stx which we want to avoid. This version works by calling memset more indirectly.

--- src/video/Xext/Xxf86vm/XF86VMode.c.orig     Mon Dec 31 04:48:09 2007
+++ src/video/Xext/Xxf86vm/XF86VMode.c  Sun Sep  7 11:48:19 2008
@@ -211,6 +211,11 @@
     return True;
 }
 
+static inline void zap_ptr(char *ptr, size_t size)
+{
+    memset(ptr, '\0', size);
+}
+
 Bool
 SDL_NAME(XF86VidModeGetModeLine)(dpy, screen, dotclock, modeline)
     Display* dpy;
@@ -281,7 +286,8 @@
        }
        _XRead(dpy, (char*)modeline->private, modeline->privsize * sizeof(INT32));
     } else {
-       modeline->private = NULL;
+       // Avoid unaligned trap on Sparc64
+       zap_ptr((char *)&modeline->private, sizeof(modeline->private));
     }
     UnlockDisplay(dpy);
     SyncHandle();
Comment 4 Brad Smith 2008-09-07 17:25:25 UTC 
Yes, that does the trick.
Comment 5 Ryan C. Gordon 2008-09-08 00:38:30 UTC 
Fixed in svn revision #4083 for the 1.2 branch, and #4084 for the 1.3 branch.

Thanks!

--ryan.
Comment 6 Ryan C. Gordon 2008-09-15 13:54:39 UTC 
svn revisions #4097 and #4098 have a hopefully-better fix for this.

--ryan.