[CMake] Enable the use of -ffile-prefix-map

[phosek]

Summary

This handles not paths embedded in debug info, but also in sources.
Since the use of this flag is controlled by an option, rather than
replacing the new option, we add a new option.

[leonardchan]

I also tried this but am still finding some paths embedded in libunwind and libclang_rt for some reason.

leonardchan@cp-snakewater:~/llvm-monorepo/llvm-build-1-master-fuchsia-toolchain$ strings ./install/lib/aarch64-unknown-fuchsia/c++/asan/libunwind.so.1.0 |& less
...
3 32 624 9 cursor:93 784 528 5 uc:94 1440 72 7 info:95
/usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-1/libunwind/src/libunwind.cpp
libunwind: %s - %s
_Unwind_Resume
_Unwind_Resume() can't return
unwind_phase2
during phase1 personality function said it would stop here, but now in phase2 it did not stop here
/usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-1/libunwind/src/UnwindLevel1.c
libunwind: %s - %s
_Unwind_Resume_or_Rethrow
...

I can assert from comparing an unstripped to the stripped binary that the __FILE__ path that we see in _LIBUNWIND_ABORT is stripped and resolved to just libunwind/src/UnwindLevel1.c, but there seems to be a separate instance of this absolute path (/usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-1/libunwind/src/UnwindLevel1.c) that I can see in the stripped binary that includes the full path.

I suppose it would be ok to submit this still since it saves space from some trimmed paths. I was hesitant to submit it yet since I haven't found a complete solution yet or figured out where this absolute path I'm finding came from.

llvm/cmake/modules/HandleLLVMOptions.cmake

1024

nit: update the name + description since it doesn't just affect debug info only now (perhaps just LLVM_USE_RELATIVE_PATHS)

I also think it would be good to add a section for this flag in llvm/docs/CMake.rst.

[phosek]

This change only covers LLVM, not the runtimes. I'll make a follow up change to do the same for runtimes which should cover the cases you mentioned.

[phosek]

@smeenai does this look reasonable to you?

[leonardchan]

Oh, I think you'll need to add it to llvm/cmake/modules/LLVMExternalProjectUtils.cmake also:

--- a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
+++ b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
@@ -221,6 +221,9 @@ function(llvm_ExternalProject_Add name source_dir)
     set(cmake_args ${ARG_CMAKE_ARGS})
   endif()

   ExternalProject_Add(${name}
     DEPENDS ${ARG_DEPENDS} llvm-config
     ${name}-clobber
@@ -239,6 +242,7 @@ function(llvm_ExternalProject_Add name source_dir)
                -DLLVM_HOST_TRIPLE=${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_USE_RELATIVE_PATHS_IN_FILES=${LLVM_USE_RELATIVE_PATHS_IN_FILES}
                -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}

[phosek]

In D76018#1930398, @leonardchan wrote:

Oh, I think you'll need to add it to llvm/cmake/modules/LLVMExternalProjectUtils.cmake also:

--- a/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
+++ b/llvm/cmake/modules/LLVMExternalProjectUtils.cmake
@@ -221,6 +221,9 @@ function(llvm_ExternalProject_Add name source_dir)
     set(cmake_args ${ARG_CMAKE_ARGS})
   endif()

   ExternalProject_Add(${name}
     DEPENDS ${ARG_DEPENDS} llvm-config
     ${name}-clobber
@@ -239,6 +242,7 @@ function(llvm_ExternalProject_Add name source_dir)
                -DLLVM_HOST_TRIPLE=${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_USE_RELATIVE_PATHS_IN_FILES=${LLVM_USE_RELATIVE_PATHS_IN_FILES}
                -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}

Good catch, done.

llvm/cmake/modules/HandleLLVMOptions.cmake

elseif( NOT DEFINED LLVM_ENABLE_SUPPORT_XCODE_SIGNPOSTS )
       # defined.
     else()
       message(FATAL_ERROR "Unknown value for LLVM_ENABLE_SUPPORT_XCODE_SIGNPOSTS:"
                           " \"${LLVM_ENABLE_SUPPORT_XCODE_SIGNPOSTS}\"!")
     endif()
   endif()
 endif()
 
+set(LLVM_SOURCE_PREFIX "" CACHE STRING "Use prefix for sources")
+
 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()
+
+option(LLVM_USE_RELATIVE_PATHS_IN_FILES "Use relative paths in sources and debug info" OFF)
+
+if(LLVM_USE_RELATIVE_PATHS_IN_FILES)
+  check_c_compiler_flag("-ffile-prefix-map=foo=bar" SUPPORTS_FFILE_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_FFILE_PREFIX_MAP "-ffile-prefix-map=${CMAKE_BINARY_DIR}=${relative_root}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  append_if(SUPPORTS_FFILE_PREFIX_MAP "-ffile-prefix-map=${source_root}/=${LLVM_SOURCE_PREFIX}" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  add_flag_if_supported("-no-canonical-prefixes" NO_CANONICAL_PREFIXES)
+endif()

llvm/cmake/modules/LLVMExternalProjectUtils.cmake

CMAKE_ARGS ${${nameCanon}_CMAKE_ARGS}
                -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
                ${sysroot_arg}
                -DLLVM_BINARY_DIR=${PROJECT_BINARY_DIR}
                -DLLVM_CONFIG_PATH=${llvm_config_path}
                -DLLVM_ENABLE_WERROR=${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=${LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO}
+               -DLLVM_USE_RELATIVE_PATHS_IN_FILES=${LLVM_USE_RELATIVE_PATHS_IN_FILES}
                -DLLVM_SOURCE_PREFIX=${LLVM_SOURCE_PREFIX}
                -DPACKAGE_VERSION=${PACKAGE_VERSION}
                -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
                -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
                -DCMAKE_EXPORT_COMPILE_COMMANDS=1
                ${cmake_args}
                ${PASSTHROUGH_VARIABLES}
     INSTALL_COMMAND ""

llvm/docs/CMake.rst

 
 **LLVM_ENABLE_BINDINGS**:BOOL
   If disabled, do not try to build the OCaml and go bindings.
 
 **LLVM_ENABLE_Z3_SOLVER**:BOOL
   If enabled, the Z3 constraint solver is activated for the Clang static analyzer.
   A recent version of the z3 library needs to be available on the system.
 
+**LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO**:BOOL
+  Rewrite absolute source paths in debug info to relative ones. The source prefix
+  can be adjusted via the LLVM_SOURCE_PREFIX variable.
+
+**LLVM_USE_RELATIVE_PATHS_IN_FILES**:BOOL
+  Rewrite absolute source paths in sources and debug info to relative ones. The
+  source prefix can be adjusted via the LLVM_SOURCE_PREFIX variable.
+
 CMake Caches
 ============
 
 Recently LLVM and Clang have been adding some more complicated build system
 features. Utilizing these new features often involves a complicated chain of
 CMake variables passed on the command line. Clang provides a collection of CMake
 cache scripts to make these features more approachable.