Bug 183072 – Clang reports undefined reference errors of poison variables while building LLIntOffsetsExtractor with -gsplit-dwarf

• Component: JavaScriptCore
• Status: RESOLVED INVALID

[Fujii Hironori]

CC=clang-5.0 CXX=clang++-5.0 ./Tools/Scripts/build-webkit --gtk --debug

> [1/2400] Linking CXX executable bin/LLIntOffsetsExtractor
> FAILED: bin/LLIntOffsetsExtractor 
> : && /usr/bin/clang++-5.0  -fdiagnostics-color=always -fcolor-diagnostics -Wno-parentheses-equality -Wno-noexcept-type -Qunused-arguments -Wwrite-strings -Wundef -Wpointer-arith -Wmissing-format-attribute -Wformat-security -Wcast-align -Wextra -Wall  -fno-strict-aliasing -fno-exceptions -std=c++14 -fno-rtti -gsplit-dwarf -g  -L/home/fujii/work/webkit/ga/WebKitBuild/DependenciesGTK/Root/lib -fuse-ld=gold -Wl,--disable-new-dtags -Wl,--gdb-index   -rdynamic Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o  -o bin/LLIntOffsetsExtractor  lib/libWTFGTK.a lib/libbmalloc.a -ldl -licudata -licui18n -licuuc -lpthread -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lz && :
> Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o(.debug_addr+0x8): error: undefined reference to 'g_NativeCodePoison'
> Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o(.debug_addr+0x10): error: undefined reference to 'g_JITCodePoison'
> Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o(.debug_addr+0x18): error: undefined reference to 'g_UnlinkedSourceCodePoison'
> Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o(.debug_addr+0x20): error: undefined reference to 'g_JSFunctionPoison'
> Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o(.debug_addr+0x28): error: undefined reference to 'g_GlobalDataPoison'
> Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o(.debug_addr+0x30): error: undefined reference to 'g_JSGlobalObjectPoison'
> Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o(.debug_addr+0x38): error: undefined reference to 'g_CodeBlockPoison'
> clang: error: linker command failed with exit code 1 (use -v to see invocation)

[Fujii Hironori]

I created a reduced LLIntOffsetsExtractor.cpp:
https://gist.github.com/fujii/9940945fc788aba2577e41eb06ec7271

This is caused by -gsplit-dwarf.

> fujii@ubuntu $ clang++-5.0 -std=c++14 -gsplit-dwarf  LLIntOffsetsExtractor.cpp
> /tmp/LLIntOffsetsExtractor-15eec5.o:(.debug_addr+0x0): undefined reference to `g_JITCodePoison'
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
> fujii@ubuntu $ clang++-5.0 -std=c++14  LLIntOffsetsExtractor.cpp
> fujii@ubuntu $

This is a document about .debug_addr.
https://gcc.gnu.org/wiki/DebugFission

[Fujii Hironori]

GTK port release builds has no problem because it doesn't use -gsplit-dwarf.

> [1/1] : && /usr/bin/clang++-5.0  -fdiagnostics-color=always -fcolor-diagnostics -Wno-parentheses-equality -Wno-noexcept-type -Qunused-arguments -Wwrite-strings -Wundef -Wpointer-arith -Wmissing-format-attribute -Wformat-security -Wcast-align -Wextra -Wall  -fno-strict-aliasing -fno-exceptions -std=c++14 -fno-rtti -O3 -DNDEBUG  -L/home/fujii/work/webkit/ga/WebKitBuild/DependenciesGTK/Root/lib -fuse-ld=gold -Wl,--disable-new-dtags   -rdynamic Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o  -o bin/LLIntOffsetsExtractor  lib/libWTFGTK.a lib/libbmalloc.a -ldl -licudata -licui18n -licuuc -lpthread -lgio-2.0 -lgobject-2.0 -lglib-2.0 -lz && :

[Fujii Hironori]

GCC doesn't seem to have this issue.

$ g++-7 -std=c++14 -gsplit-dwarf  LLIntOffsetsExtractor.cpp

[Fujii Hironori]

Created attachment 334505 [details]
Patch

[EWS Watchlist]

Attachment 334505 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/llint/LLIntOffsetsExtractor.cpp:68:  POISON_KEY_NAME is incorrectly named. Don't use underscores in your identifier names.  [readability/naming/underscores] [4]
Total errors found: 1 in 2 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Mark Lam]

Comment on attachment 334505 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=334505&action=review

> Source/JavaScriptCore/llint/LLIntOffsetsExtractor.cpp:69
> +#define DEFINE_POISON(poisonID) \
> +    uintptr_t POISON_KEY_NAME(poisonID);
> +FOR_EACH_JSC_POISON(DEFINE_POISON)

Why is this necessary at all?  We don't ever use these as offsets.  So, I find it suspicious that we need them here.

Secondly, the LLInt asm code only refers to them as global addresses that should come from the JavaScriptCore library.  Fabricating a second set of such variables here in LLIntOffsetsExtractor will only at best stop the compiler from complaining, but any addresses or offsets generated from these will have nothing to do with the versions in the JavaScriptCore library.  As such, you'll definitely be getting wrong values.  Hence, I'm not sure that this is not the right solution.  r- for now.

Can you explain what -gsplit-dwarf is and what does it have to do with triggering this issue?

[Fujii Hironori]

I don't see this issue with the latest GTK port. Closed as INVALID.