cmake: Set CMAKE_INSTALL_RPATH in Clang when building separately from LLVM

[plevine]

Summary

LLVM sets CMAKE_INSTALL_RPATH in its top-level CMakeLists.txt to "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}". When Clang is built with LLVM, this propagates to Clang as well and ensures that even if CMAKE_INSTALL_PREFIX is set, installed binaries always find their dependent libraries.

When compiling clang as a separately build, no such rpath is set. If CMAKE_INSTALL_PREFIX is not set and libraries are installed to standard locations, this is not a problem. But when defining CMAKE_INSTALL_PREFIX, even if the same as that of LLVM, and installing and then executing binaries like clang, it results in

error while loading shared libraries: libLLVMBPFCodeGen.so.4.0: cannot open shared object file: No such file or directory

In the case of using a separate CMAKE_INSTALL_PREFIX from LLVM's, eg., "/usr/lib/clang-4.0.0", the build needs rpaths for both its own libraries and that of LLVM. The build should set "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}:${LLVM_LIBRARY_DIR}" as the rpath in the general case. The rpath section was taken and modified from the top-level LLVM CMakeLists.txt.

[mgorny]

I presume you copied it out of LLVM. If that's the case, please add an comment above stating where it's been copied from.

[plevine]

In D25267#561955, @mgorny wrote:

I presume you copied it out of LLVM. If that's the case, please add an comment above stating where it's been copied from.

Yes. I copied it from LLVM's top-level CMakeLists.txt and added ${LLVM_LIBRARY_DIR} to the rpath.

[beanz]

This is actually not the right fix here. We should actually fix this in LLVM to setup the rpath correctly on the targets during llvm_add_executable, then we can remove this hack from LLVM instead of copying it to Clang. It might also let us fix the RPATH goop in other tools too.

[plevine]

In D25267#562941, @beanz wrote:

This is actually not the right fix here. We should actually fix this in LLVM to setup the rpath correctly on the targets during llvm_add_executable, then we can remove this hack from LLVM instead of copying it to Clang. It might also let us fix the RPATH goop in other tools too.

Submitted for review: https://reviews.llvm.org/D25304

[plevine]

Fixed with rL285714.

CMakeLists.txt

if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
   set(LLVM_LIBRARY_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})
   if(WIN32 OR CYGWIN)
     # DLL platform -- put DLLs into bin.
     set(LLVM_SHLIB_OUTPUT_INTDIR ${LLVM_RUNTIME_OUTPUT_INTDIR})
   else()
     set(LLVM_SHLIB_OUTPUT_INTDIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
   endif()
 
+  set(CMAKE_BUILD_WITH_INSTALL_RPATH OFF)
+  if (APPLE)
+    set(CMAKE_INSTALL_NAME_DIR "@rpath")
+    set(CMAKE_INSTALL_RPATH "@executable_path/../lib:${LLVM_LIBRARY_DIR}")
+  else(UNIX)
+    if(NOT DEFINED CMAKE_INSTALL_RPATH)
+      set(CMAKE_INSTALL_RPATH "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}:${LLVM_LIBRARY_DIR}")
+      if(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)")
+        set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-z,origin")
+        set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-z,origin")
+      endif()
+    endif(NOT DEFINED CMAKE_INSTALL_RPATH)
+  endif()
+
   option(LLVM_INSTALL_TOOLCHAIN_ONLY
     "Only include toolchain files in the 'install' target." OFF)
 
   option(LLVM_FORCE_USE_OLD_HOST_TOOLCHAIN
     "Set to ON to force using an old, unsupported host toolchain." OFF)
   option(CLANG_ENABLE_BOOTSTRAP "Generate the clang bootstrap target" OFF)
 
   include(AddLLVM)