Fix LLVM_ENABLE_PIC under Unix/Linux

[aguinet]

Summary

The -pie linker flag must be set, or the final binary isn't PIE.

[chill]

Hello,

Per https://llvm.org/docs/DeveloperPolicy.html and https://llvm.org/docs/Phabricator.html
llvm-commits mailing list should be added as a Subscriber.

Also, take a look at CODE_OWNERS.txt and/or last few people to have touched this code and around it (git blame) and add them as reviewers.

Best regards,
chill

[aguinet]

Hello Chill,

Sorry about missing llvm-commits as a reviewer (I think I missed it while reading the links you provided).

IIRC, I had also added @momchil.velikov (which means you :)) as a reviewer because git blame "blamed" you at the time :)

cmake/modules/HandleLLVMOptions.cmake

if( LLVM_ENABLE_PIC )
   if( XCODE )
     # Xcode has -mdynamic-no-pic on by default, which overrides -fPIC. I don't
     # know how to disable this, so just force ENABLE_PIC off for now.
     message(WARNING "-fPIC not supported with Xcode.")
   elseif( WIN32 OR CYGWIN)
     # On Windows all code is PIC. MinGW warns if -fPIC is used.
   else()
     add_flag_or_print_warning("-fPIC" FPIC)
+    append("-pie"
+      CMAKE_EXE_LINKER_FLAGS CMAKE_MODULE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
   endif()
 endif()
 
 if(NOT WIN32 AND NOT CYGWIN)
   # MinGW warns if -fvisibility-inlines-hidden is used.
   check_cxx_compiler_flag("-fvisibility-inlines-hidden" SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG)
   append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG "-fvisibility-inlines-hidden" CMAKE_CXX_FLAGS)
 endif()