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

[phosek]

Summary

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.

[phosek]

llvm/runtimes/CMakeLists.txt

455

We should probably only enable this for ELF targets since that's the only one that currently supports the .build-id scheme.

llvm/runtimes/llvm-strip-link.in

14

@jakehehrlich llvm-objcopy complains when you give it unrecognized file as an input, in our case it's libc++.so which is a linker script. Is there a better way to do this?

[jakehehrlich]

LGTM

llvm/runtimes/llvm-strip-link.in

14

No this is the best way I can think to do it. If a file starts with the elf magic it's highly unlikely to be anything else, and certainly it won't be a linker script so I think this is good.

[smeenai]

Build parts look good to me.

llvm/cmake/modules/LLVMExternalProjectUtils.cmake

38

I think STRIP_TOOL or STRIP_PATH or STRIP_TOOL_PATH would be more standard, but I don't care too much.

[smeenai]

LLVM already has LLVM_EXTERNALIZE_DEBUGINFO, btw ... idk if that could be easily extended for this use case.

[smeenai]

llvm/runtimes/CMakeLists.txt

455

Yup.

[phosek]

I've updated the patch to make the .build-id linking an option that can be set in the cache file, how does that look to you?

[smeenai]

LGTM

llvm/runtimes/CMakeLists.txt

436

list(APPEND)

llvm/cmake/modules/LLVMExternalProjectUtils.cmake

 #   TOOLCHAIN_TOOLS targets...
 #     Targets for toolchain tools (defaults to clang;lld)
 #   DEPENDS targets...
 #     Targets that this project depends on
 #   EXTRA_TARGETS targets...
 #     Extra targets in the subproject to generate targets for
 #   PASSTHROUGH_PREFIXES prefix...
 #     Extra variable prefixes (name is always included) to pass down
+#   USE_STRIP path
+#     Use provided strip tool/script 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;USE_STRIP"
     ${ARGN})
   canonicalize_tool_name(${name} nameCanon)
   if(NOT ARG_TOOLCHAIN_TOOLS)
     set(ARG_TOOLCHAIN_TOOLS clang lld)
     if(NOT APPLE AND NOT WIN32)
       list(APPEND ARG_TOOLCHAIN_TOOLS llvm-ar llvm-ranlib llvm-nm llvm-objcopy llvm-objdump llvm-strip)
     endif()
   endif()
if(llvm-nm IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_NM=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-nm)
     endif()
     if(llvm-objdump IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_OBJDUMP=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-objdump)
     endif()
     if(llvm-objcopy IN_LIST TOOLCHAIN_TOOLS)
       list(APPEND compiler_args -DCMAKE_OBJCOPY=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-objcopy)
     endif()
-    if(llvm-strip IN_LIST TOOLCHAIN_TOOLS)
+    if(llvm-strip IN_LIST TOOLCHAIN_TOOLS AND NOT ARG_USE_STRIP)
       list(APPEND compiler_args -DCMAKE_STRIP=${LLVM_RUNTIME_OUTPUT_INTDIR}/llvm-strip)
     endif()
     list(APPEND ARG_DEPENDS ${TOOLCHAIN_TOOLS})
   endif()
 
+  if(ARG_USE_STRIP)
+    list(APPEND compiler_args -DCMAKE_STRIP=${ARG_USE_STRIP})
+  endif()
+
   add_custom_command(
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp
     DEPENDS ${ARG_DEPENDS}
     COMMAND ${CMAKE_COMMAND} -E touch ${BINARY_DIR}/CMakeCache.txt
     COMMAND ${CMAKE_COMMAND} -E touch ${STAMP_DIR}/${name}-mkdir
     COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp
     COMMENT "Clobbering bootstrap build and stamp directories"
     )

llvm/runtimes/CMakeLists.txt

foreach(entry ${runtimes})
 
     string(FIND ${projName} "lib" LIB_IDX)
     if(LIB_IDX EQUAL 0)
       string(SUBSTRING ${projName} 3 -1 projName)
     endif()
     list(APPEND runtime_names ${projName})
   endforeach()
 
+  configure_file(
+    ${CMAKE_CURRENT_SOURCE_DIR}/llvm-strip-link.in
+    ${CMAKE_CURRENT_BINARY_DIR}/llvm-strip-link
+    @ONLY
+  )
+
   function(runtime_default_target)
     cmake_parse_arguments(ARG "" "" "DEPENDS;PREFIXES" ${ARGN})
 
     include(${LLVM_BINARY_DIR}/runtimes/Components.cmake OPTIONAL)
     set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${LLVM_BINARY_DIR}/runtimes/Components.cmake)
 
     foreach(runtime_name ${runtime_names})
       list(APPEND extra_targets
foreach(variableName ${variableNames})
         list(APPEND ${name}_extra_args "-D${new_name}=${${variableName}}")
       elseif(variableName MATCHES "^RUNTIMES_${target}")
         string(REPLACE "RUNTIMES_${target}_" "" new_name ${variableName})
         list(APPEND ${name}_extra_args "-D${new_name}=${${variableName}}")
       endif()
     endforeach()
 
     llvm_ExternalProject_Add(runtimes-${name}
                              ${CMAKE_CURRENT_SOURCE_DIR}
                              DEPENDS ${${name}_deps}
                              # Builtins were built separately above
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_LIBRARY_DIR=${LLVM_LIBRARY_DIR}
                                         -DLLVM_DEFAULT_TARGET_TRIPLE=${target}
                                         -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON
                                         -DCMAKE_C_COMPILER_TARGET=${target}
                                         -DCMAKE_CXX_COMPILER_TARGET=${target}
                                         -DCMAKE_ASM_COMPILER_TARGET=${target}
                                         -DCMAKE_C_COMPILER_WORKS=ON
                                         -DCMAKE_CXX_COMPILER_WORKS=ON
                                         -DCMAKE_ASM_COMPILER_WORKS=ON
                                         -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON
                                         -DLLVM_RUNTIMES_TARGET=${name}
                                         ${${name}_extra_args}
                              PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                              TOOLCHAIN_TOOLS clang lld llvm-ar llvm-ranlib llvm-nm llvm-objcopy llvm-objdump llvm-strip
+                             USE_STRIP ${CMAKE_CURRENT_BINARY_DIR}/llvm-strip-link
                              EXTRA_TARGETS ${${name}_extra_targets}
                                            ${${name}_test_targets}
                              USE_TOOLCHAIN
                              ${EXTRA_ARGS})
   endfunction()
 
   if(runtimes)
     # Create a runtimes target that uses this file as its top-level CMake file.

llvm/runtimes/llvm-strip-link.in

+#!/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],
+]))