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

[Lobron, David]

Hey All-

The -fgnu-runtime is for using the runtime that comes with the GNU compiler (gcc).

More specifically, it is for telling GCC to use the runtime that comes with GCC.  If you wish to use the GCC runtime with clang, the correct flag is -fobjc-runtime=gcc (optionally with a version, though clang currently ignores the version because it doesn’t know of any changes to the GCC runtime ABI since clang shipped - I don’t think there are any).

I just wanted to let people know that this was fixed when I upgrade my gnustep-make from 2.6.x to 2.7.0, which has support for the --with-library-combo=ng-gnu-gnu option.  That stopped the -fgnu-runtime flag from being issued, and C++ exceptions now work in my ObjC++ code.

I did encounter one other issue: the linker complained that it could not find libobjcxx.so.4.6, needed by libobjc.so, even though those are in the same directory, and there is a "libobjcxx.so" symlink that points to libobjcxx.so.4.6.  The directory is being specified in the -L options, and it's clearly being found, because libobjc.so is found there:

$ ls -l libobj*
lrwxrwxrwx 1 dlobron staff     14 Dec  1 16:08 libobjc.so -> libobjc.so.4.6
-rw-r--r-- 1 dlobron staff 246455 Dec  1 16:08 libobjc.so.4.6
lrwxrwxrwx 1 dlobron staff     16 Dec  1 16:08 libobjcxx.so -> libobjcxx.so.4.6
-rw-r--r-- 1 dlobron staff  19112 Dec  1 16:08 libobjcxx.so.4.6

I worked around this by adding "-l :libobjcxx.so" to my link options, which fixed the problem.  However, I'm curious as to why the linker doesn't find libobjcxx.so on its own, without the explicit -l prompt.  I've copied the link command and error below, in case any compiler/linker expert has knowledge of this.

Thanks again for all the help here.

--David

Linker error that occurs when linking my program:

/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang++  -rdynamic     -m64  -rdynamic  -pthread  -fexceptions -fobjc-runtime=gnustep-1.8 -fblocks -o obj/mapmaker \
                ./obj/mapmaker.obj/FirstPointDomainAdditions.m.o ./obj/mapmaker.obj/PropertyInstanceAdditions.m.o ./obj/mapmaker.obj/DsaRebaser.mm.o ./obj/mapmaker.obj/DynamicConfig.mm.o ./obj/mapmaker.obj/GeoTreeParser.mm.o ./obj/mapmaker.obj/FallBackTreeRebaser.mm.o ./obj/mapmaker.obj/IpWatchRebaser.mm.o ./obj/mapmaker.obj/LivenessModificationRebaser.mm.o ./obj/mapmaker.obj/LoadBalancer_config.mm.o ./obj/mapmaker.obj/LoadBalancer.mm.o ./obj/mapmaker.obj/LocalityTreeRebaser.mm.o ./obj/mapmaker.obj/MapMaker.mm.o ./obj/mapmaker.obj/MapMakerMainFunc.mm.o ./obj/mapmaker.obj/MappingDecision.mm.o ./obj/mapmaker.obj/NameserverAssociationMessage.mm.o ./obj/mapmaker.obj/NameserverAssociationRebaser.mm.o ./obj/mapmaker.obj/NSDemandsRebaser.mm.o ./obj/mapmaker.obj/PingScoresRebaser.mm.o ./obj/mapmaker.obj/PingState.mm.o ./obj/mapmaker.obj/RegionSelector.mm.o ./obj/mapmaker.obj/ResourceAdditions.mm.o ./obj/mapmaker.obj/ResourceInstanceAdditions.mm.o ./obj/mapmaker.obj/RunningAverage.mm.o ./obj/mapmaker.obj/ScoreList.mm.o ./obj/mapmaker.obj/SelectCenters.mm.o ./obj/mapmaker.obj/Statistics.mm.o ./obj/mapmaker.obj/StatisticsXMLWriter.mm.o ./obj/mapmaker.obj/TimeOfDayRebaser.mm.o ./GeoMap/obj/subproject.o ./Resources/obj/subproject.o ./Utils/obj/subproject.o \
                  -L../common/lib    -L/home/dlobron/GNUstep/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/System/Library/Libraries   -lFirstPointKit -lAkamaiKit -lXMLKit -lgtmcidrdbv6 -lloadbalancer -lmapmessagestracecollector -lmapdispatch -lcci -lmapmessagesdatacenterstate -lmapmessagesmapmakerheavymappingsummary -lmapmessagesnameserverassociation -lmapmessagesrdp -lswanslib -lmaputils -lmapuuid -lmapfilelog -lradtreev6 -lakamai -lasci -laks -lakautil -lakastack -lopenssl -lz -lunwind -lbfd -liberty -lresolv -lpthread   -lgnustep-base   -lpthread -lobjc -fobjc-nonfragile-abi   -lm
/usr/bin/ld.bfd.real: ./obj/mapmaker.obj/DsaRebaser.mm.o: undefined reference to symbol '_ZTVN7gnustep7libobjc22__objc_class_type_infoE'
/home/dlobron/build/clangport/akamai/common/lib/libobjcxx.so.4.6: error adding symbols: DSO missing from command line
clang-6.0: error: linker command failed with exit code 1 (use -v to see invocation)

The symbol is in libobjcxx.so:

$ nm -C ../common/lib/libobjcxx.so|grep -i objc_class_type_i|grep typeinfo
0000000000202d20 D typeinfo for gnustep::libobjc::__objc_class_type_info
0000000000001d40 R typeinfo name for gnustep::libobjc::__objc_class_type_info

Linking works when "-l :libobjcxx.so" is added:

$ cat link.sh
#!/bin/bash

/home/dlobron/build/clangport/akamai/llvm/llvm-5.0.0.install/bin/clang++  -rdynamic     -m64  -rdynamic  -pthread  -fexceptions -fobjc-runtime=gnustep-1.8 -fblocks -o obj/mapmaker \
./obj/mapmaker.obj/FirstPointDomainAdditions.m.o ./obj/mapmaker.obj/PropertyInstanceAdditions.m.o ./obj/mapmaker.obj/DsaRebaser.mm.o ./obj/mapmaker.obj/DynamicConfig.mm.o ./obj/mapmaker.obj/GeoTreeParser.mm.o ./obj/mapmaker.obj/FallBackTreeRebaser.mm.o ./obj/mapmaker.obj/IpWatchRebaser.mm.o ./obj/mapmaker.obj/LivenessModificationRebaser.mm.o ./obj/mapmaker.obj/LoadBalancer_config.mm.o ./obj/mapmaker.obj/LoadBalancer.mm.o ./obj/mapmaker.obj/LocalityTreeRebaser.mm.o ./obj/mapmaker.obj/MapMaker.mm.o ./obj/mapmaker.obj/MapMakerMainFunc.mm.o ./obj/mapmaker.obj/MappingDecision.mm.o ./obj/mapmaker.obj/NameserverAssociationMessage.mm.o ./obj/mapmaker.obj/NameserverAssociationRebaser.mm.o ./obj/mapmaker.obj/NSDemandsRebaser.mm.o ./obj/mapmaker.obj/PingScoresRebaser.mm.o ./obj/mapmaker.obj/PingState.mm.o ./obj/mapmaker.obj/RegionSelector.mm.o ./obj/mapmaker.obj/ResourceAdditions.mm.o ./obj/mapmaker.obj/ResourceInstanceAdditions.mm.o ./obj/mapmaker.obj/RunningAverage.mm.o ./obj/mapmaker.obj/ScoreList.mm.o ./obj/mapmaker.obj/SelectCenters.mm.o ./obj/mapmaker.obj/Statistics.mm.o ./obj/mapmaker.obj/StatisticsXMLWriter.mm.o ./obj/mapmaker.obj/TimeOfDayRebaser.mm.o ./GeoMap/obj/subproject.o ./Resources/obj/subproject.o ./Utils/obj/subproject.o \
-l :libobjcxx.so \
-L../common/lib    -L/home/dlobron/GNUstep/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/Local/Library/Libraries -L/home/dlobron/build/clangport/akamai/common/GNUstep/System/Library/Libraries   -lFirstPointKit -lAkamaiKit -lXMLKit -lgtmcidrdbv6 -lloadbalancer -lmapmessagestracecollector -lmapdispatch -lcci -lmapmessagesdatacenterstate -lmapmessagesmapmakerheavymappingsummary -lmapmessagesnameserverassociation -lmapmessagesrdp -lswanslib -lmaputils -lmapuuid -lmapfilelog -lradtreev6 -lakamai -lasci -laks -lakautil -lakastack -lopenssl -lz -lunwind -lbfd -liberty -lresolv -lpthread   -lgnustep-base   -lpthread -lobjc -fobjc-nonfragile-abi   -lm

$ ./link.sh
$