Build libFuzzer with -fPIC

[george.karpenkov]

Summary

Strangely enough, otherwise we get the following linker error only on Linux only when using Swift:

...
/usr/bin/ld.gold: error: /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@2/branch-master-next/buildbot_linux/swift-linux-x86_64/lib/swift/clang/lib/linux/libclang_rt.fuzzer-x86_64.a(FuzzerDriver.cpp.o): requires unsupported dynamic reloc 11; recompile with -fPIC
/usr/bin/ld.gold: error: /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@2/branch-master-next/buildbot_linux/swift-linux-x86_64/lib/swift/clang/lib/linux/libclang_rt.fuzzer-x86_64.a(FuzzerDriver.cpp.o): requires unsupported dynamic reloc 11; recompile with -fPIC
/usr/bin/ld.gold: error: /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@2/branch-master-next/buildbot_linux/swift-linux-x86_64/lib/swift/clang/lib/linux/libclang_rt.fuzzer-x86_64.a(FuzzerDriver.cpp.o): requires dynamic R_X86_64_PC32 reloc against '_Znwm' which may overflow at runtime; recompile with -fPIC
/usr/bin/ld.gold: error: /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@2/branch-master-next/buildbot_linux/swift-linux-x86_64/lib/swift/clang/lib/linux/libclang_rt.fuzzer-x86_64.a(FuzzerDriver.cpp.o): requires dynamic R_X86_64_PC32 reloc against '_ZdlPv' which may overflow at runtime; recompile with -fPIC
/usr/bin/ld.gold: error: /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@2/branch-master-next/buildbot_linux/swift-linux-x86_64/lib/swift/clang/lib/linux/libclang_rt.fuzzer-x86_64.a(FuzzerDriver.cpp.o): requires dynamic R_X86_64_PC32 reloc against '_ZdlPv' which may overflow at runtime; recompile with -fPIC
/usr/bin/ld.gold: error: /home/buildnode/jenkins/workspace/swift-PR-Linux-smoke-test@2/branch-master-next/buildbot_linux/swift-linux-x86_64/lib/swift/clang/lib/linux/libclang_rt.fuzzer-x86_64.a(FuzzerDriver.cpp.o): requires dynamic R_X86_64_32 reloc against '_ZTSSt19_Sp_make_shared_tag' which may overflow at runtime; recompile with -fPIC
...

[kcc]

of course. :)

Please add a lit test that builds a puzzle with "-fPIC -pie", such test should fail w/o this change.
The change itself LGTM, thanks!

[george.karpenkov]

@kcc I can't get the test to fail without this option: -fPIC -pie does not seem to be enough.

[kcc]

Actually, running ninja -v on linux gives me this command line:
clang++ -D_DEBUG -D_GNU_SOURCE -DSTDC_CONSTANT_MACROS -DSTDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Iprojects/compiler-rt/lib/fuzzer -I/usr/local/google/home/kcc/llvm/projects/compiler-rt/lib/fuzzer -I/usr/include/libxml2 -Iinclude -I/usr/local/google/home/kcc/llvm/include -fPIC -fvisibility-inlines-hidden -Werror=date-time -std=c++11 -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fcolor-diagnostics -ffunction-sections -fdata-sections -Wall -std=c++11 -Wno-unused-parameter -O3 -UNDEBUG -fPIC -fvisibility-inlines-hidden -Werror=date-time -std=c++11 -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fcolor-diagnostics -ffunction-sections -fdata-sections -Wall -std=c++11 -Wno-unused-parameter -m64 -MMD -MT projects/compiler-rt/lib/fuzzer/CMakeFiles/RTfuzzer.x86_64.dir/FuzzerLoop.cpp.o -MF projects/compiler-rt/lib/fuzzer/CMakeFiles/RTfuzzer.x86_64.dir/FuzzerLoop.cpp.o.d -o projects/compiler-rt/lib/fuzzer/CMakeFiles/RTfuzzer.x86_64.dir/FuzzerLoop.cpp.o -c /usr/local/google/home/kcc/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp

I.e. -fPIC is already there.
No surprise you can't make a test fail.
But it *is* is surprise why this change fixes anything.

[kcc]

LGTM

[george.karpenkov]

Abandoned in favor of https://reviews.llvm.org/D37225

lib/fuzzer/CMakeLists.txt

CHECK_CXX_SOURCE_COMPILES("
   " HAS_THREAD_LOCAL)
 
 if (CMAKE_CXX_FLAGS MATCHES "fsanitize-coverage")
   set(LIBFUZZER_CFLAGS -fno-sanitize-coverage=trace-pc-guard,edge,trace-cmp,indirect-calls,8bit-counters)
 endif()
 if(NOT HAS_THREAD_LOCAL)
   set(LIBFUZZER_CFLAGS "${LIBFUZZER_CFLAGS} -Dthread_local=__thread")
 endif()
+set(LIBFUZZER_CFLAGS "${LIBFUZZER_CFLAGS} -fPIC")
 
 if(APPLE)
   set(FUZZER_SUPPORTED_OS osx)
 endif()
 
 add_compiler_rt_object_libraries(RTfuzzer
   OS ${FUZZER_SUPPORTED_OS}
   ARCHS ${FUZZER_SUPPORTED_ARCH}