Index: cfe/trunk/cmake/caches/Fuchsia-stage2.cmake
===================================================================
--- cfe/trunk/cmake/caches/Fuchsia-stage2.cmake
+++ cfe/trunk/cmake/caches/Fuchsia-stage2.cmake
@@ -15,6 +15,7 @@
 set(LLVM_EXTERNALIZE_DEBUGINFO ON CACHE BOOL "")
 set(LLVM_INCLUDE_EXAMPLES OFF CACHE BOOL "")
 set(LLVM_INCLUDE_DOCS OFF CACHE BOOL "")
+set(LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO ON CACHE BOOL "")
 
 set(CLANG_DEFAULT_CXX_STDLIB libc++ CACHE STRING "")
 if(NOT APPLE)
Index: llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
+++ llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
@@ -977,3 +977,19 @@
     endif()
   endif()
 endif()
+
+option(LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO "Use relative paths in debug info" OFF)
+set(LLVM_SOURCE_PREFIX "" CACHE STRING "Use prefix for sources in debug info")
+
+if(LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO)
+  check_c_compiler_flag("-fdebug-prefix-map=foo=bar" SUPPORTS_FDEBUG_PREFIX_MAP)
+  if(LLVM_ENABLE_PROJECTS_USED)
+    get_filename_component(source_root "${LLVM_MAIN_SRC_DIR}/.." ABSOLUTE)
+  else()
+    set(source_root "${LLVM_MAIN_SRC_DIR}")
+  endif()
+  file(RELATIVE_PATH relative_root "${source_root}" "${CMAKE_BINARY_DIR}")
+  append_if(SUPPORTS_FDEBUG_PREFIX_MAP "-fdebug-prefix-map=${CMAKE_BINARY_DIR}=${relative_root}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  append_if(SUPPORTS_FDEBUG_PREFIX_MAP "-fdebug-prefix-map=${source_root}/=${LLVM_SOURCE_PREFIX}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  add_flag_if_supported("-no-canonical-prefixes" NO_CANONICAL_PREFIXES)
+endif()
Index: llvm/trunk/cmake/modules/LLVMExternalProjectUtils.cmake
===================================================================
--- llvm/trunk/cmake/modules/LLVMExternalProjectUtils.cmake
+++ llvm/trunk/cmake/modules/LLVMExternalProjectUtils.cmake
@@ -231,6 +231,8 @@
                -DLLVM_ENABLE_WERROR=${LLVM_ENABLE_WERROR}
                -DLLVM_HOST_TRIPLE=${LLVM_HOST_TRIPLE}
                -DLLVM_HAVE_LINK_VERSION_SCRIPT=${LLVM_HAVE_LINK_VERSION_SCRIPT}
+               -DLLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO=${LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO}
+               -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
                -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
Index: llvm/trunk/runtimes/CMakeLists.txt
===================================================================
--- llvm/trunk/runtimes/CMakeLists.txt
+++ llvm/trunk/runtimes/CMakeLists.txt
@@ -375,6 +375,7 @@
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${TARGET_TRIPLE}
+                                        -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                         -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
                                         -DCMAKE_C_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_CXX_COMPILER_TARGET=${TARGET_TRIPLE}
@@ -464,6 +465,7 @@
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${target}
+                                        -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                         -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
                                         -DCMAKE_C_COMPILER_TARGET=${target}
                                         -DCMAKE_CXX_COMPILER_TARGET=${target}