Re: Mysterious crash in NSRunLoop, using libobjc2 on Linux

[Lobron, David]

>> The line in frame 2 is a NS_ENDHANDLER call, inside of a method called  "- 
>> (NSDate*) limitDateForMode: (NSString*)mode".  There's no call to abort in 
>> that code.  I tried stepping line by line, but I did not see any exception 
>> being thrown here.
> 
> _Unwind_Resume is the function that is used to resume stack unwinding after a 
> cleanup.  It should only be called in Objective-C code at the end of an 
> @finally block (with no corresponding catch block, just @try { … @throw … } 
> @finally {}) or as the result of using __attribute__((cleanup)).
> 
> I believe that if you are targetting the gnustep runtime prior to 1.7 (or 
> using a very old version of clang), it will be emitted by clang, but I don’t 
> remember precisely what the EH ABI looked like before I fixed it (I think it 
> called objc_exception_throw(), not _Unwind_Resume).

I'm targeting the gnustep-1.8 in my gnustep-make flags, and all of my own code 
is being built with -fobjc-runtime=gnustep-1.8.  However, I now see that a few 
.o files in libobjc2 are being compiled with -fobjc-runtime=gnustep-1.7 rather 
than 1.8.  Could that be the problem?  I've copied those compile commands at 
the end of this message.  I'm using clang-6.0.0, from llvm-5.0.0, which should 
be the latest stable version.

> Please can you use a debug build of libobjc2 (that should prevent tail-call 
> optimisation) and stick a breakpoint on _Unwind_Resume and see where it’s 
> called from? 

Done.  The last few lines of the backtrace look like this:

#0  _Unwind_Resume (exc=0xa6c82e0) at ../../../src/libgcc/unwind.inc:224
#1  0x00007ffff6f2851d in -[RadixTree 
initWithFileDescriptor:symbolParserFunction:context:] (self=<optimized out>, 
_cmd=<optimized out>, fd=<optimized out>, 
    parser=0x4d2430 <parsePingTreeSymbol(NSString*, void*)>, context=0x2dee800) 
at RadixTree.mm:863
#2  0x00000000004d23e7 in -[PingTreeParser pingTreeWithFile:] 
(self=0x7fffffffb998, _cmd=<optimized out>, path=0x0) at PingState.mm:305

RadixTree.mm is a file from my own codebase.  Line 863 of that code is an 
NS_ENDHANDLER block.  The lines leading up to, and including, line 863 look 
like this:

        readTree(self, _root, indexMap);
        gzclose(_gzFile);
        _gzFile = 0;
    } NS_HANDLER {
        [self release];
        [localException retain];
        [pool release];
        [[localException autorelease] raise];
    } NS_ENDHANDLER

I can send a longer excerpt if it would be helpful.  The code itself has been 
around a long time, and has worked under gcc/gnu runtime for a long time.  
Also, it's running fine with clang/libobjc2 on a number of similar inputs in 
other unit tests- it's just this one particular test that triggers the 
SIGABORT.  

Is there another debugging step I might take here, or does this output suggest 
the source of the problem?

Thank you,

David

Possibly problematic compile lines that target gnustep-1.7:

/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang 
-DGC_DEBUG -DGNUSTEP -DNO_LEGACY -DTYPE_DEPENDENT_DISPATCH -D_BSD_SOURCE=1 
-D_XOPEN_SOURCE=700 -D__BSD_VISIBLE=1 -D__OBJC_RUNTIME_INTERNAL__=1 
-Dobjc_EXPORTS  -std=gnu99  -fexceptions -g -O0 -fno-inline -g -fPIC    
-Wno-deprecated-objc-isa-usage -Wno-objc-root-class -fobjc-runtime=gnustep-1.7 
-o CMakeFiles/objc.dir/Protocol2.m.o   -c 
/home/dlobron/build/clangport/akamai/libobjc2/libobjc2-1.8.1/Protocol2.m
[ 82%] Building ASM object CMakeFiles/objc.dir/objc_msgSend.S.o
/usr/bin/clang -DGC_DEBUG -DGNUSTEP -DNO_LEGACY -DTYPE_DEPENDENT_DISPATCH 
-D_BSD_SOURCE=1 -D_XOPEN_SOURCE=700 -D__BSD_VISIBLE=1 
-D__OBJC_RUNTIME_INTERNAL__=1 -Dobjc_EXPORTS  -c   -o 
CMakeFiles/objc.dir/objc_msgSend.S.o -c 
/home/dlobron/build/clangport/akamai/libobjc2/libobjc2-1.8.1/objc_msgSend.S
[ 85%] Building C object CMakeFiles/objc.dir/arc.m.o
/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang 
-DGC_DEBUG -DGNUSTEP -DNO_LEGACY -DTYPE_DEPENDENT_DISPATCH -D_BSD_SOURCE=1 
-D_XOPEN_SOURCE=700 -D__BSD_VISIBLE=1 -D__OBJC_RUNTIME_INTERNAL__=1 
-Dobjc_EXPORTS  -std=gnu99  -fexceptions -g -O0 -fno-inline -g -fPIC    
-Wno-deprecated-objc-isa-usage -Wno-objc-root-class -fobjc-runtime=gnustep-1.7 
-o CMakeFiles/objc.dir/arc.m.o   -c 
/home/dlobron/build/clangport/akamai/libobjc2/libobjc2-1.8.1/arc.m
[ 88%] Building C object CMakeFiles/objc.dir/associate.m.o
/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang 
-DGC_DEBUG -DGNUSTEP -DNO_LEGACY -DTYPE_DEPENDENT_DISPATCH -D_BSD_SOURCE=1 
-D_XOPEN_SOURCE=700 -D__BSD_VISIBLE=1 -D__OBJC_RUNTIME_INTERNAL__=1 
-Dobjc_EXPORTS  -std=gnu99  -fexceptions -g -O0 -fno-inline -g -fPIC    
-Wno-deprecated-objc-isa-usage -Wno-objc-root-class -fobjc-runtime=gnustep-1.7 
-o CMakeFiles/objc.dir/associate.m.o   -c 
/home/dlobron/build/clangport/akamai/libobjc2/libobjc2-1.8.1/associate.m
[ 91%] Building C object CMakeFiles/objc.dir/blocks_runtime.m.o
/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang 
-DGC_DEBUG -DGNUSTEP -DNO_LEGACY -DTYPE_DEPENDENT_DISPATCH -D_BSD_SOURCE=1 
-D_XOPEN_SOURCE=700 -D__BSD_VISIBLE=1 -D__OBJC_RUNTIME_INTERNAL__=1 
-Dobjc_EXPORTS  -std=gnu99  -fexceptions -g -O0 -fno-inline -g -fPIC    
-Wno-deprecated-objc-isa-usage -Wno-objc-root-class -fobjc-runtime=gnustep-1.7 
-o CMakeFiles/objc.dir/blocks_runtime.m.o   -c 
/home/dlobron/build/clangport/akamai/libobjc2/libobjc2-1.8.1/blocks_runtime.m
[ 94%] Building C object CMakeFiles/objc.dir/properties.m.o
/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang 
-DGC_DEBUG -DGNUSTEP -DNO_LEGACY -DTYPE_DEPENDENT_DISPATCH -D_BSD_SOURCE=1 
-D_XOPEN_SOURCE=700 -D__BSD_VISIBLE=1 -D__OBJC_RUNTIME_INTERNAL__=1 
-Dobjc_EXPORTS  -std=gnu99  -fexceptions -g -O0 -fno-inline -g -fPIC    
-Wno-deprecated-objc-isa-usage -Wno-objc-root-class -fobjc-runtime=gnustep-1.7 
-o CMakeFiles/objc.dir/properties.m.o   -c 
/home/dlobron/build/clangport/akamai/libobjc2/libobjc2-1.8.1/properties.m
[ 97%] Building C object CMakeFiles/objc.dir/gc_none.c.o
/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang 
-DGC_DEBUG -DGNUSTEP -DNO_LEGACY -DTYPE_DEPENDENT_DISPATCH -D_BSD_SOURCE=1 
-D_XOPEN_SOURCE=700 -D__BSD_VISIBLE=1 -D__OBJC_RUNTIME_INTERNAL__=1 
-Dobjc_EXPORTS  -std=gnu99  -fexceptions -g -O0 -fno-inline -g -fPIC    
-Wno-deprecated-objc-isa-usage -Wno-objc-root-class -fobjc-runtime=gnustep-1.7 
-o CMakeFiles/objc.dir/gc_none.c.o   -c 
/home/dlobron/build/clangport/akamai/libobjc2/libobjc2-1.8.1/gc_none.c
[100%] Linking C shared library libobjc.so