[PATCH] D82733: [clang][docs] Add note about using `-flto` with `-g` on macOS

[Philippe Blain via Phabricator via cfe-commits]

phil-blain created this revision.
phil-blain added reviewers: echristo, dblaikie.
Herald added subscribers: dexonsmith, inglorion.
Herald added a reviewer: JDevlieghere.
Herald added a project: clang.

If `-Wl,object_path_lto,<lto-filename>.o` is not passed at link time
when compiling and linking in separate steps with `-flto` and `-g`, the
temporary file used for Link Time Optimization is deleted by the linker,
so the executable is missing debug symbols and can't be easily debugged,
and `dsymutil` can't be run.

Document this behaviour.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D82733

Files:
  clang/docs/CommandGuide/clang.rst


Index: clang/docs/CommandGuide/clang.rst
===================================================================
--- clang/docs/CommandGuide/clang.rst
+++ clang/docs/CommandGuide/clang.rst
@@ -474,6 +474,14 @@
   optimization. With "thin", :doc:`ThinLTO <../ThinLTO>`
   compilation is invoked instead.
 
+  Note: on Darwin, when using :option:`-flto` along with :option:`-g` and
+  compiling and linking in separate steps, you also need to pass
+  `-Wl,object_path_lto,<lto-filename>.o` at the linking step to instruct the
+  ld64 linker not to delete the temporary object file generated during Link
+  Time Optimization (this flag is automatically passed to the linker by Clang
+  if compilation and linking are done in a single step). This allows debugging
+  the executable as well as generating the `.dSYM` bundle using :manpage:`dsymutil(1)`.
+
 Driver Options
 ~~~~~~~~~~~~~~
 


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