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Bug 1056

Summary: Frequent crashes in Touch events by simply touching the screen (currently in iPhone Simulator)
Product: SDL Reporter: Pavel Kanzelsberger <kanzels>
Component: eventsAssignee: Sam Lantinga <slouken>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: critical    
Priority: P2 CC: joseba.gar, kanzels
Version: HG 2.0   
Hardware: iPhone/iPod touch   
OS: iOS 3   

Description Pavel Kanzelsberger 2010-09-21 06:41:30 UTC 
Program received signal:  “EXC_BAD_ACCESS”.
(gdb) bt
#0  0x000e995b in SDL_GetFingerIndexId (touch=0x0, fingerid=97068992) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/events/SDL_touch.c:67
#1  0x000e999a in SDL_GetFinger (touch=0x0, id=97068992) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/events/SDL_touch.c:77
#2  0x000ea41b in SDL_SendTouchMotion (id=1, fingerid=97068992, relative=0, xin=181, yin=158, pressurein=1) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/events/SDL_touch.c:400
#3  0x000c2f0c in -[SDL_uikitview touchesMoved:withEvent:] (self=0x5c5ed70, _cmd=0x221dc6c, touches=0x70830e0, event=0x5c16020) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/video/uikit/SDL_uikitview.m:190
#4  0x008ca2a9 in -[UIWindow _sendTouchesForEvent:] ()
#5  0x008ac1ec in -[UIApplication sendEvent:] ()
#6  0x008b0ac4 in _UIApplicationHandleEvent ()
#7  0x03e43afa in PurpleEventCallback ()
#8  0x029f2dc4 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
#9  0x02953737 in __CFRunLoopDoSource1 ()
#10 0x029509c3 in __CFRunLoopRun ()
#11 0x02950280 in CFRunLoopRunSpecific ()
#12 0x029501a1 in CFRunLoopRunInMode ()
#13 0x000c1f6b in UIKit_PumpEvents (_this=0x6041200) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/video/uikit/SDL_uikitevents.m:51
#14 0x0006ffff in SDL_PumpEvents () at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/events/SDL_events.c:434
#15 0x0007006e in SDL_WaitEventTimeout (event=0xbfffdc60, timeout=-1) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/events/SDL_events.c:468
#16 0x00070047 in SDL_WaitEvent (event=0xbfffdc60) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/events/SDL_events.c:456
#17 0x00008267 in GUI_MAINLOOP (POLL=false, CALLBACKS=false) at gui.s:2771
#18 0x000120a3 in GUI_LAYOUTDEFAULTCALLBACK_MOUSEBUTTON (LAYOUT=0xdd56420, OBJ=0x0, TAB=-1, X=171, Y=7, BUTTONS=1) at gui.s:25161
#19 0x0001158b in GUI_LAYOUTMOUSEBUTTONDOWN (LAYOUT=0xdd56420, X=181, Y=157, BUTTONS=1) at gui.s:23671
#20 0x0000839e in GUI_MAINLOOP (POLL=false, CALLBACKS=4294967295) at gui.s:2866
#21 0x00008c47 in GUI_RUNAPP () at gui.s:3563
#22 0x00006776 in APPSTART () at PascalLibrary.s:5227
#23 0x0000251f in SDL_main (argc=1, argv=0x5c0f680) at /Users/pavel/Projects/iPhone/iPhoneEAGL/main.m:14
#24 0x000c44cf in -[SDLUIKitDelegate postFinishLaunch] (self=0x5c18530, _cmd=0x196850) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/video/uikit/SDL_uikitappdelegate.m:75
#25 0x0260dcea in __NSFireDelayedPerform ()
#26 0x029f2d43 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ ()
#27 0x029f4384 in __CFRunLoopDoTimer ()
#28 0x02950d09 in __CFRunLoopRun ()
#29 0x02950280 in CFRunLoopRunSpecific ()
#30 0x029501a1 in CFRunLoopRunInMode ()
#31 0x03e422c8 in GSEventRunModal ()
#32 0x03e4238d in GSEventRun ()
#33 0x008b4b58 in UIApplicationMain ()
#34 0x000c43d8 in main (argc=1, argv=0xbffff004) at /Users/pavel/Sources/SDL/Xcode-iPhoneOS/SDL/../../src/video/uikit/SDL_uikitappdelegate.m:53
Comment 1 Joseba García Echebarria 2010-12-15 01:55:22 UTC 
I believe the crash is caused by a check not being performed on wether an SDL_Touch element is NULL before using it in the SDL_SendTouchMotion function in src/events/SDL_touch.c around line 400.
Judging from the rest of the code, there's a missing

    if (!touch) {
        return 0;
    }

before using "touch" as SDL_GetFinger(), SDL_GetFingerIndexId() use touch->num_fingers without checking.

I can attach a patch if you like. It seems pretty straightforward, though.

I have yet to discover why touch is being returned as NULL as this error is only triggered when an actual gesture has been performed, maybe something related to SDL_AddTouch()?

If it serves of any help I'm compiling from standard Makefile's, not from XCode. The "Touch" and "Fireworks" demos in the repository seem to be working fine when compiled from Xcode.
I will try to compile those examples with my Makefile to see if missing compilation flags are to be blamed for this.
Comment 2 Joseba García Echebarria 2010-12-17 03:41:14 UTC 
As additional info, this was happening in iOS 4.2 too, the additional check fixes the crash.
Comment 3 Sam Lantinga 2011-01-28 10:22:44 UTC 
This is fixed in the repository, thanks!