Occasional crash when foregrounding modal GUI app

[Patryk Laurent]

Hello,

Building GNUstep from the latest source (last commit of libs-gui is Jul 28),  clicking to foreground a just-launched modal alert view app occasionally crashes. The app tries to raise an exception and for some reason this is triggering an abort. 

The app is being compiled with ARC, libobjc2 1.9, on Aarch64. 

Oddly, sometimes when running this test in lldb, upon clicking or alt-tabbing to foreground the app instead of an abort I see that the process was “stopped and restarted” with “thread 1 received signal: SIGCHLD” and the app continues to run. 

(1) Does anyone understand by libs-gui would be occasionally throwing this exception in the first place?  Could it be some kind of race condition?

(2) Why would the exception throwing result in an abort()?  (Please see stack trace below).

Thank you,

Patryk

(lldb) run

Process 11479 launched: '/home/patryk/Desktop/gnustep-build/GUITest.app/GUITest' (aarch64)

Process 11479 stopped

* thread #1, name = 'GUITest', stop reason = signal SIGABRT

    frame #0: 0x0000007fb65e5528 libc.so.6`gsignal + 56

libc.so.6`gsignal:

->  0x7fb65e5528 <+56>: cmn    x0, #0x1, lsl #12         ; =0x1000 

    0x7fb65e552c <+60>: b.hi   0x7fb65e5550              ; <+96>

    0x7fb65e5530 <+64>: ret    

    0x7fb65e5534 <+68>: nop    

(lldb) fr va

(lldb) up

frame #1: 0x0000007fb65e69e0 libc.so.6`abort + 432

libc.so.6`abort:

    0x7fb65e69e0 <+432>: add    x0, x19, #0x9d8           ; =0x9d8 

    0x7fb65e69e4 <+436>: ldr    x1, [x0, #0x8]

    0x7fb65e69e8 <+440>: cmp    x20, x1

    0x7fb65e69ec <+444>: b.eq   0x7fb65e6a20              ; <+496>

(lldb) up

frame #2: 0x0000007fb67bcc08 libobjc.so.4.6`objc_exception_throw(object=0x0000000000d3b808) at eh_personality.c:188

   185 _objc_unexpected_exception(object);

   186 }

   187 DEBUG_LOG("Throw returned %d\n",(int) err);

-> 188 abort();

   189 }

   190 

   191 static Class get_type_table_entry(struct _Unwind_Context *context,

(lldb) up

frame #3: 0x0000007fb6c53268 libgnustep-base.so.1.26`-[NSException raise](self=0x0000000000d3b808, _cmd="\x85") at NSException.m:1513

   1510     }

   1511

   1512 #if     defined(_NATIVE_OBJC_EXCEPTIONS)

-> 1513   @throw self;

   1514 #else

   1515 {

   1516   NSThread      *thread;

(lldb) up

frame #4: 0x0000007fb77b8fd8 libgnustep-gui.so.0.27`-[NSApplication runModalForWindow:](self=0x0000000000806d78, _cmd="z\x1c", theWindow=0x0000000000aac598) at NSApplication.m:1808

   1805 }

   1806       if ([[localException name] isEqual: NSAbortModalException] == NO)

   1807 {

-> 1808   [localException raise];

   1809     } 

   1810       code = NSRunAbortedResponse;

   1811     }

(lldb) up

frame #5: 0x0000007fb77985bc libgnustep-gui.so.0.27`-[NSAlert runModal](self=0x00000000009d9ad8, _cmd="`\x1c") at NSAlert.m:2016

   2013   else

   2014     {

   2015       [self _setupPanel];

-> 2016       [NSApp runModalForWindow: _window];

   2017       [_window orderOut: self];

   2018       _result = [(GSAlertPanel*)_window result];

   2019       DESTROY(_window);

(lldb) up

frame #6: 0x0000000000401018 GUITest`main at guitest.m:11

   8     NSAlert * alert = [[NSAlert alloc] init];

   9     [alert setMessageText:@"Hello alert"];

   10    [alert addButtonWithTitle:@"All done"];

-> 11    int result = [alert runModal];

   12    if (result == NSAlertFirstButtonReturn) {

   13      NSLog(@"First button pressed");

   14    }

(lldb)