[CMake] Support stripping and linking output to .build-id directory

When installing runtimes with install-runtimes-stripped, we don't want
to just strip them, we also want to preserve the debugging information
for potential debugging. To make it possible to later find the stripped
debugging information, we want to use the .build-id layout:

https://fedoraproject.org/wiki/RolandMcGrath/BuildID#Find_files_by_build_ID

That is, for libfoo.so with build ID abcdef1234, the debugging information
will be installed into lib/debug/.build-id/ab/cdef1234. llvm-objcopy
already has support for stripping files and linking the debugging
stripped output into the right location. However, CMake doesn't support
customizing strip invocation for the *-stripped targets. So instead, we
replace CMAKE_STRIP with a custom script that invokes llvm-objcopy with
the right command line flags.

Differential Revision: https://reviews.llvm.org/D59127

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355765 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/LLVMExternalProjectUtils.cmake

@@ -35,12 +35,14 @@ endfunction()
 #     Extra targets in the subproject to generate targets for
 #   PASSTHROUGH_PREFIXES prefix...
 #     Extra variable prefixes (name is always included) to pass down
+#   STRIP_TOOL path
+#     Use provided strip tool instead of the default one.
 #   )
 function(llvm_ExternalProject_Add name source_dir)
   cmake_parse_arguments(ARG
     "USE_TOOLCHAIN;EXCLUDE_FROM_ALL;NO_INSTALL;ALWAYS_CLEAN"
     "SOURCE_DIR"
-    "CMAKE_ARGS;TOOLCHAIN_TOOLS;RUNTIME_LIBRARIES;DEPENDS;EXTRA_TARGETS;PASSTHROUGH_PREFIXES"
+    "CMAKE_ARGS;TOOLCHAIN_TOOLS;RUNTIME_LIBRARIES;DEPENDS;EXTRA_TARGETS;PASSTHROUGH_PREFIXES;STRIP_TOOL"
     ${ARGN})
   canonicalize_tool_name(${name} nameCanon)
   if(NOT ARG_TOOLCHAIN_TOOLS)
@@ -125,12 +127,16 @@ function(llvm_ExternalProject_Add name source_dir)
     if(llvm-objcopy IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_OBJCOPY=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-objcopy)
     endif()
-    if(llvm-strip IN_LIST TOOLCHAIN_TOOLS)
+    if(llvm-strip IN_LIST TOOLCHAIN_TOOLS AND NOT ARG_STRIP_TOOL)
       list(APPEND compiler_args -DCMAKE_STRIP=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-strip)
     endif()
     list(APPEND ARG_DEPENDS ${TOOLCHAIN_TOOLS})
   endif()
 
+  if(ARG_STRIP_TOOL)
+    list(APPEND compiler_args -DCMAKE_STRIP=${ARG_STRIP_TOOL})
+  endif()
+
   add_custom_command(
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp
     DEPENDS ${ARG_DEPENDS}

runtimes/CMakeLists.txt

@@ -318,6 +318,14 @@ else() # if this is included from LLVM's CMake
     list(APPEND runtime_names ${projName})
   endforeach()
 
+  if(LLVM_RUNTIME_BUILD_ID_LINK_TARGETS)
+    configure_file(
+      ${CMAKE_CURRENT_SOURCE_DIR}/llvm-strip-link.in
+      ${CMAKE_CURRENT_BINARY_DIR}/llvm-strip-link
+      @ONLY
+    )
+  endif()
+
   function(runtime_default_target)
     cmake_parse_arguments(ARG "" "" "DEPENDS;PREFIXES" ${ARGN})
 
@@ -426,6 +434,10 @@ else() # if this is included from LLVM's CMake
       endif()
     endforeach()
 
+    if(target IN_LIST LLVM_RUNTIME_BUILD_ID_LINK_TARGETS)
+      list(APPEND EXTRA_ARGS STRIP_TOOL ${CMAKE_CURRENT_BINARY_DIR}/llvm-strip-link)
+    endif()
+
     llvm_ExternalProject_Add(runtimes-${name}
                              ${CMAKE_CURRENT_SOURCE_DIR}
                              DEPENDS ${${name}_deps}

runtimes/llvm-strip-link.in

@@ -0,0 +1,27 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+import os
+import sys
+import subprocess
+
+
+ELF_MAGIC = '\x7fELF'
+
+with open(sys.argv[1], "rb") as f:
+    buf = f.read(len(ELF_MAGIC))
+    if buf != ELF_MAGIC:
+        sys.exit(0)
+
+llvm_objcopy = os.path.join('@LLVM_RUNTIME_OUTPUT_INTDIR@', 'llvm-objcopy')
+install_dir = os.path.join(os.getenv('DESTDIR', ''), '@CMAKE_INSTALL_PREFIX@')
+link_dir = os.path.join(install_dir, 'lib', 'debug', '.build-id')
+
+sys.exit(subprocess.call([
+    llvm_objcopy,
+    '--strip-sections',
+    '--build-id-link-dir=' + link_dir,
+    '--build-id-link-input=.debug',
+    '--build-id-link-output=',
+    sys.argv[1],
+]))