[llvm] Align LLVM_EXTERNALIZE_DEBUGINFO_EXTENSION behaviour on Linux w/ Darwin (PR #75059)

[Jo Shields via llvm-commits]

https://github.com/directhex created https://github.com/llvm/llvm-project/pull/75059

Ported from D111740

Despite what it says in the documentation[1], LLVM_EXTERNALIZE_DEBUGINFO is not only for Darwin, and has been functional on Linux since 2017[2].

However, it is hardcoded to emit ${name}.debug in the same directory, whereas macOS allows overriding both the extension and the output dir.

This commit adds support for LLVM_EXTERNALIZE_DEBUGINFO_EXTENSION and LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR on Linux.

[1] https://www.llvm.org/docs/CMake.html#llvm-related-variables
[2] https://reviews.llvm.org/D28575

>From 42ab239d087b7d77805d2bf8b67ea84081c050b7 Mon Sep 17 00:00:00 2001
From: Jo Shields <directhex at apebox.org>
Date: Mon, 11 Dec 2023 09:55:37 -0500
Subject: [PATCH] Ported from D111740

Despite what it says in the documentation[1], LLVM_EXTERNALIZE_DEBUGINFO is not only for Darwin, and has been functional on Linux since 2017[2].

However, It is hardcoded to emit ${name}.debug in the same directory, whereas macOS allows overriding both the extension and the output dir.

This commit adds support for LLVM_EXTERNALIZE_DEBUGINFO_EXTENSION and LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR on Linux.

[1] https://www.llvm.org/docs/CMake.html#llvm-related-variables
[2] https://reviews.llvm.org/D28575
---
 llvm/cmake/modules/AddLLVM.cmake | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index c9bca30c8f33d1..d8307c2b4b63a1 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -2293,10 +2293,28 @@ function(llvm_externalize_debuginfo name)
       ${strip_command}
       )
   else()
+    if(LLVM_EXTERNALIZE_DEBUGINFO_EXTENSION)
+      set(file_ext ${LLVM_EXTERNALIZE_DEBUGINFO_EXTENSION})
+    else()
+      set(file_ext debug)
+    endif()
+    set(output_name "$<TARGET_FILE_NAME:${name}>.${file_ext}")
+    if(LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR)
+      set(output_path "${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}/${output_name}")
+      # If an output dir is specified, it must be manually mkdir'd on Linux,
+      # as that directory needs to exist before we can pipe to a file in it.
+      add_custom_command(TARGET ${name} POST_BUILD
+        WORKING_DIRECTORY ${LLVM_RUNTIME_OUTPUT_INTDIR}
+        COMMAND ${CMAKE_COMMAND} -E make_directory ${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}
+        )
+    else()
+      set(output_path "${output_name}")
+    endif()
     add_custom_command(TARGET ${name} POST_BUILD
-      COMMAND ${CMAKE_OBJCOPY} --only-keep-debug $<TARGET_FILE:${name}> $<TARGET_FILE:${name}>.debug
+      WORKING_DIRECTORY ${LLVM_RUNTIME_OUTPUT_INTDIR}
+      COMMAND ${CMAKE_OBJCOPY} --only-keep-debug $<TARGET_FILE:${name}> ${output_path}
       ${strip_command} -R .gnu_debuglink
-      COMMAND ${CMAKE_OBJCOPY} --add-gnu-debuglink=$<TARGET_FILE:${name}>.debug $<TARGET_FILE:${name}>
+      COMMAND ${CMAKE_OBJCOPY} --add-gnu-debuglink=${output_path} $<TARGET_FILE:${name}>
       )
   endif()
 endfunction()