[LLVMdev] Gold plugin and LLVM tools documentation

[Todd Jackson]

On Tue, May 1, 2012 at 1:32 PM, Rafael Espíndola
<rafael.espindola at gmail.com> wrote:
>> First, I create libjscore.a with ar, where I've changed the command
>> line to load the plugin:
>> ar cqs --plugin
>> /home/tmjackso/multicompiler/llvm-3.0/release/lib/LLVMgold.so
>> libjscore.a <list of object files>
>
> Note that you shouldn't need to pass --plugin to ar, it searches bfd-plugins.

Ok.  I'll keep that in mind, but I'll leave it in for now.

>> Then I link jsc against libjscore.a:
>> /home/tmjackso/multicompiler/llvm-3.0/release/bin/clang++
>> -Wl,-plugin,/home/tmjackso/multicompiler/llvm-3.0/release/lib/LLVMgold.so
>> -Wl,-rpath,/home/tmjackso/builds/qt/qt-4.8.1/lib
>> -Wl,-rpath,/home/tmjackso/builds/webkit/WebKit-r94287/WebKitBuild/Release/lib
>> -o ./jsc obj/release/jsc.o    -L./release
>> -L/home/tmjackso/builds/qt/qt-4.8.1/lib -ljscore -lQtCore
>> -L/home/tmjackso/builds/qt/qt-4.8.1/lib -lpthread
>> /usr/bin/ld: error: jscore: malformed archive header name at 8
>>
>> When I change the link command to not use "-ljscore" but the path to
>> libjscore.a, it works:
>> /home/tmjackso/multicompiler/llvm-3.0/release/bin/clang++
>> -Wl,-plugin,/home/tmjackso/multicompiler/llvm-3.0/release/lib/LLVMgold.so
>> -Wl,-rpath,/home/tmjackso/builds/qt/qt-4.8.1/lib
>> -Wl,-rpath,/home/tmjackso/builds/webkit/WebKit-r94287/WebKitBuild/Release/lib
>> -o ./jsc obj/release/jsc.o libjscore.a  -L./release
>> -L/home/tmjackso/builds/qt/qt-4.8.1/lib -lQtCore
>> -L/home/tmjackso/builds/qt/qt-4.8.1/lib -lpthread
>>
>> Does anyone know what I'm doing wrong in the first case? The build is
>> managed by qmake, and I'm working on coaxing it into generating the
>> second line.
>
> What does ld -v shows? Can you run nm on  libjscore.a?

$ ld -v
GNU gold (GNU Binutils 2.22) 1.11

Without passing --plugin to nm:
$ nm WebKitBuild/Release/JavaScriptCore/release/libjscore.a
nm: YarrInterpreter.o: File format not recognized
nm: YarrPattern.o: File format not recognized
nm: YarrSyntaxChecker.o: File format not recognized
nm: Assertions.o: File format not recognized
nm: ByteArray.o: File format not recognized
nm: CryptographicallyRandomNumber.o: File format not recognized
...
(...etc)

With passing --plugin to nm:
$ nm --plugin /home/tmjackso/multicompiler/llvm-3.0/release/lib/LLVMgold.so
WebKitBuild/Release/JavaScriptCore/release/libjscore.a | head -n 5

YarrInterpreter.o:
         U WTFReportBacktrace
00000000 W _ZN3JSC4Yarr11Interpreter16matchDisjunctionEPNS0_15ByteDisjunctionEPNS1_18DisjunctionContextEb
00000000 W _ZN3JSC4Yarr11Interpreter16matchParenthesesERNS0_8ByteTermEPNS1_18DisjunctionContextE
00000000 W _ZN3JSC4Yarr11Interpreter17matchAssertionEOLERNS0_8ByteTermE
...

> Not a lot has changed. You should be able to pass -flto when linking
> to causes clang to pass the plugin to the linker automatically btw.

This is what I get when I use just -flto -v:
$ /home/tmjackso/multicompiler/llvm-3.0/release/bin/clang++ -flto -v
-Wl,-rpath,/home/tmjackso/builds/webkit/WebKit-r94287/WebKitBuild/Release/lib
-o ./jsc obj/release/jsc.o    -L./release -L/usr/lib/x86_64-linux-gnu
-ljscore -lQtCore -lpthread
clang version 3.0
(ssh://tmjackso@ssllab.org/gitroot/multicompiler/clang.git
8c04ba90b6edfc97cedd7eae248c91775687805b)
Target: x86_64-unknown-linux-gnu
Thread model: posix
 "/usr/bin/ld" -z relro --hash-style=gnu --build-id --eh-frame-hdr -m
elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o ./jsc
/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/4.6/crtbegin.o -L./release
-L/usr/lib/x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/4.6
-L/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu
-L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/4.6/../../.. -L/lib/x86_64-linux-gnu
-L/lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib -rpath
/home/tmjackso/builds/webkit/WebKit-r94287/WebKitBuild/Release/lib
obj/release/jsc.o -ljscore -lQtCore -lpthread -lstdc++ -lm -lgcc_s
-lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/4.6/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/crtn.o
/usr/bin/ld: error: obj/release/jsc.o:1:3: invalid character
/usr/bin/ld: error: obj/release/jsc.o:1:3: syntax error, unexpected $end
/usr/bin/ld: error: obj/release/jsc.o: not an object or archive
/usr/bin/ld: error: jscore: no archive symbol table (run ranlib)
/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/crt1.o(.text+0x20):
error: undefined reference to 'main'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

When I use -flto -v -Wl,-plugin, it links successfully.

Thanks,

Todd