[docs] Add ARM64X release notes (NFC)

[cjacek]

No description provided.

[llvmorg-github-actions]

@llvm/pr-subscribers-lld

Author: Jacek Caban (cjacek)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/209249.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.md (+5)
• (modified) lld/docs/ReleaseNotes.rst (+8)
• (modified) llvm/docs/ReleaseNotes.md (+3)

diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index bbd42848a98c2..754de16430f5a 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -467,6 +467,11 @@ latest release, please see the [Clang Web Site](https://clang.llvm.org) or the
   "1". The previous functionality remains unchanged.
 - The `-fms-kernel` flag will now implicitly add `-fno-delete-null-pointer-checks`.
   Still `-fdelete-null-pointer-checks` can be used to override this behavior.
+- Extended the `-marm64x` flag to support compiling to object files. When used
+  in this mode, separate compilation jobs are run for ARM64 and ARM64EC object
+  files, which are then merged into a single file using a new `.obj.arm64ec`
+  section. Consumers must support this extension. Currently, this requires
+  LLD for linking or `llvm-ar`/`llvm-lib` for archiving.
 
 ### Removed Compiler Flags
 
diff --git a/lld/docs/ReleaseNotes.rst b/lld/docs/ReleaseNotes.rst
index 058173413e41a..c873fea2cc1b7 100644
--- a/lld/docs/ReleaseNotes.rst
+++ b/lld/docs/ReleaseNotes.rst
@@ -63,6 +63,9 @@ Breaking changes
 COFF Improvements
 -----------------
 
+* Added support for ``.obj.arm64ec`` sections to allow embedding ARM64EC object
+  files inside ARM64 object files.
+
 MinGW Improvements
 ------------------
 
@@ -70,6 +73,11 @@ MinGW Improvements
   when used with the ELF linker: The state of ``--Bstatic``/``--Bdynamic`` and
   ``--whole-archive`` are pushed onto a stack and popped from it.
 
+* Added the ``--native-def`` option to specify the native module-definition
+  file for ARM64X targets. If a module-definition file is passed without this
+  option, it is used for both native and EC views. ``--native-def=`` can be
+  used to prevent the native view from using the default file.
+
 MachO Improvements
 ------------------
 
diff --git a/llvm/docs/ReleaseNotes.md b/llvm/docs/ReleaseNotes.md
index 4548be37e7f4c..2d24cbc5fc3a3 100644
--- a/llvm/docs/ReleaseNotes.md
+++ b/llvm/docs/ReleaseNotes.md
@@ -400,6 +400,9 @@ Makes programs 10x faster by doing Special New Thing.
 * Fixed `llvm-ar` to correctly handle the `N` count modifier on Windows for archive members whose names differ only
   in case (e.g. `FOO.OBJ` and `foo.obj`). Previously, `-N 2` would fail with "not found" even when two matching members existed.
 * `llvm-readobj` and `llvm-readelf` now support the `--call-graph-section` option to dump the contents of the experimental [call graph section](CallGraphSection.md).
+* Added support for hybrid ARM64X object files to `llvm-ar` and `llvm-lib`. When these files are added to
+  an archive, they are automatically split into separate native and EC members. Because the resulting members
+  are no longer hybrid object files, consumers of these archives do not need to support the hybrid format themselves.
 
 ### Changes to LLDB
 

[mstorsjo]

LGTM, thanks! Very nice.