Re: Crash occurs when catching std::exception in Objective-C++ code compiled with clang on Linux and using libobjc2

[David Chisnall]

On 16 Nov 2017, at 20:50, Lobron, David <dlobron@akamai.com> wrote:
> 
> Hi David and gnustep,
> 
>> This test case works perfectly for me on FreeBSD, where clang defaults to 
>> -fobjc-runtime=gnustep.  It segfaults if I add -fobjc-runtime=gcc.  This is 
>> entirely expected, because the GCC ABI for exceptions is makes it impossible 
>> to correctly interop with C++ (I spent a few weeks trying and it always 
>> fails for at least some of the corner cases).  If you specify 
>> -fobjc-runtime=gnustep-1.8, then it will work correctly.
> 
> I updated my gnustep-make (version 2.6.0) to include 
> -fobjc-runtime=gnustep-1.8 in ADDITIONAL_FLAGS, with the following change to 
> common.make:
> 
> 728a729,732
> > # Specify the gnustep-1.8 runtime so we pick up the correct exception 
> > personalities
> > # in ObjCC.
> > ADDITIONAL_FLAGS += -fobjc-runtime=gnustep-1.8 
> 
> This works as expected, as this sample compilation line that has the 
> -fobjc-runtime=gnustep-1.8 flag:
> 
> /home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang++ 
> ResourceAdditions.mm -c \
>       -MMD -MP -idirafter 
> /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/ext -DGNUSTEP 
> -DGNUSTEP_BASE_LIBRARY=1 -DGNU_RUNTIME=1 -DGNUSTEP_BASE_LIBRARY=1 
> -fno-strict-aliasing -fPIC -Wall -DGSWARN -DGSDIAGNOSE -Wno-import 
> -fobjc-runtime=gnustep-1.8 -mfpmath=sse -msse2 -fno-strict-aliasing -Wall 
> -Werror -Wno-multichar -DHAVE_CONFIG_H -D_GNU_SOURCE -m64 -march=opteron 
> -mno-3dnow -ggdb -O2 -Wall -fPIC -fPIC -fgnu-runtime -std=c++11 
> -fconstant-string-class=NSConstantString -I ../common/include -I. 
> -I/home/dlobron/GNUstep/Library/Headers 
> -I/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Headers 
> -I/home/dlobron/build/clangport/akamai/common/GNUstep/System/Library/Headers
> 
> However, I'm still getting the same result: C++ exception objects are nil 
> when caught in Objective-C++ code (.mm files).  As I mentioned, I'm using 
> libobjc2 and building with clang.  This error does not occur when I build 
> with gcc, nor with clang on a Mac - only clang on Linux.
> 
> Is it possible that some key part of my compilation is missing 
> -fobjc-runtime=gnustep-1.8?  It appears everywhere I can think to look, and 
> ADDITIONAL_FLAGS does seem like the right place to put it.  Please let me 
> know if there is something else I might check.  I did notice that the flag 
> "-fgnu-runtime" appears in my compilation line - could that value be 
> incorrect?

-fgnu-runtime is long-deprecated, and I’m not sure what happens if it’s 
specified *after* -fobjc-runtime=.  It may override it (and default to an 
earlier runtime target).  It’s probably best to remove it.

Did you run the libobjc2 tests (which include a test for C++ exceptions in 
Objective-C++), and did they pass?

David