[lld-macho] Release notes for 15.x

[int3]

Summary

From inspection of

git log origin/release/14.x..origin/release/15.x -- lld/MachO

[int3]

[thakis]

LG.

Want to add that we now support $ld$previous symbols with symbols name? (Not yet merged to 15.0, but will be). ("Programs using swift linked with the 14.0 sdk but an older deployment target no longer crash at startup when running on older iOS versions" or something like that.)

[int3]

mention diff too

[int3]

Good point, done :)

[int3]

Closed by https://github.com/llvm/llvm-project/commit/b128f6feaa467e9f1f53c995848b7b750d00dd23.

[thakis]

Wait, isn't this also missing the eh frame support? (And maybe the release notes should mention the new clang flag to emit less eh free data too?)

There are a lot of cool changes in this release :)

[int3]

Oh that was already added previously. See the first bullet point right above the changes in this diff

But yes, there are a lot of cool changes :D

lld/docs/ReleaseNotes.rst

 ------------------
 
 * We now support proper relocation and pruning of EH frames. **Note:** this
   comes at some performance overhead on x86_64 builds, and we recommend adding
   the ``-femit-compact-unwind=no-compact-unwind`` compile flag to avoid it.
   (`D129540 <https://reviews.llvm.org/D129540>`_,
   `D122258 <https://reviews.llvm.org/D122258>`_)
 
+New flags
+#########
+
+* ``-load_hidden`` and ``-hidden-l`` are now supported.
+  (`D130473 <https://reviews.llvm.org/D130473>`_,
+  `D130529 <https://reviews.llvm.org/D130529>`_)
+* ``-alias`` is now supported. (`D129938 <https://reviews.llvm.org/D129938>`_)
+* ``-no_exported_symbols`` and  ``-exported_symbols_list <empty file>`` are now
+  supported. (`D127562 <https://reviews.llvm.org/D127562>`_)
+* ``-w`` -- to suppress warnings -- is now supported.
+  (`D127564 <https://reviews.llvm.org/D127564>`_)
+* ``-non_global_symbols_strip_list``, ``-non_global_symbols_no_strip_list``, and
+  ``-x`` are now supported. (`D126046 <https://reviews.llvm.org/D126046>`_)
+* ``--icf=safe`` is now supported.
+  (`D128938 <https://reviews.llvm.org/D128938>`_,
+  `D123752 <https://reviews.llvm.org/D123752>`_)
+* ``-why_live`` is now supported.
+  (`D120377 <https://reviews.llvm.org/D120377>`_)
+* ``-pagezero_size`` is now supported.
+  (`D118724 <https://reviews.llvm.org/D118724>`_)
+
+Improvements
+############
+
+* Linker optimization hints are now supported.
+  (`D129427 <https://reviews.llvm.org/D129427>`_,
+  `D129059 <https://reviews.llvm.org/D129059>`_,
+  `D128942 <https://reviews.llvm.org/D128942>`_,
+  `D128093 <https://reviews.llvm.org/D128093>`_)
+* Rebase opcodes are now encoded more compactly.
+  (`D130180 <https://reviews.llvm.org/D130180>`_,
+  `D128798 <https://reviews.llvm.org/D128798>`_)
+* C-strings are now aligned more compactly.
+  (`D121342 <https://reviews.llvm.org/D121342>`_)
+* ``--deduplicate-literals`` (and ``--icf={safe,all}``) now fold the
+  ``__cfstring`` section.
+  (`D130134  <https://reviews.llvm.org/D130134>`_,
+  `D120137 <https://reviews.llvm.org/D120137>`_)
+* ICF now folds the ``__objc_classrefs`` section.
+  (`D121053 <https://reviews.llvm.org/D121053>`_)
+* ICF now folds functions with identical LSDAs.
+  (`D129830 <https://reviews.llvm.org/D129830>`_)
+* STABS entries for folded functions are now omitted.
+  (`D123252 <https://reviews.llvm.org/D123252>`_)
+* ``__objc_imageinfo`` sections are now folded.
+  (`D130125 <https://reviews.llvm.org/D130125>`_)
+* Dylibs with ``LC_DYLD_EXPORTS_TRIE`` can now be read.
+  (`D129430 <https://reviews.llvm.org/D129430>`_)
+* Writing zippered dylibs is now supported.
+  (`D124887 <https://reviews.llvm.org/D124887>`_)
+* C-string literals are now included in the mapfile.
+  (`D118077 <https://reviews.llvm.org/D118077>`_)
+* Symbol names in several more diagnostics are now demangled.
+  (`D130490 <https://reviews.llvm.org/D130490>`_,
+  `D127110 <https://reviews.llvm.org/D127110>`_,
+  `D125732 <https://reviews.llvm.org/D125732>`_)
+* Source information is now included in symbol error messages.
+  (`D128425 <https://reviews.llvm.org/D128425>`_,
+  `D128184 <https://reviews.llvm.org/D128184>`_)
+* Numerous other improvements were made to diagnostic messages.
+  (`D127753 <https://reviews.llvm.org/D127753>`_,
+  `D127696 <https://reviews.llvm.org/D127696>`_,
+  `D127670 <https://reviews.llvm.org/D127670>`_,
+  `D118903 <https://reviews.llvm.org/D118903>`_,
+  `D118798 <https://reviews.llvm.org/D118798>`_)
+* Many performance and memory improvements were made.
+  (`D130000 <https://reviews.llvm.org/D130000>`_,
+  `D128298 <https://reviews.llvm.org/D128298>`_,
+  `D128290 <https://reviews.llvm.org/D128290>`_,
+  `D126800 <https://reviews.llvm.org/D126800>`_,
+  `D126785 <https://reviews.llvm.org/D126785>`_,
+  `D121052 <https://reviews.llvm.org/D121052>`_)
+* Order files and call graph sorting can now be used together.
+  (`D117354 <https://reviews.llvm.org/D117354>`_)
+* Give LTO more precise symbol resolutions, which allows optimizations to be
+  more effective.
+  (`D119506 <https://reviews.llvm.org/D119506>`_,
+  `D119372 <https://reviews.llvm.org/D119372>`_,
+  `D119767 <https://reviews.llvm.org/D119767>`_)
+* Added partial support for linking object files built with DTrace probes.
+  (`D129062 <https://reviews.llvm.org/D129062>`_)
+
+Fixes
+#####
+
+* Programs using Swift linked with the 14.0 SDK but an older deployment target
+  no longer crash at startup when running on older iOS versions. This is because
+  we now correctly support ``$ld$previous`` symbols that contain an explicit
+  symbol name. (`D130725 <https://reviews.llvm.org/D130725>`_)
+* Match ld64's behavior when an archive is specified both via
+  ``LC_LINKER_OPTION`` and via the command line.
+  (`D129556 <https://reviews.llvm.org/D129556>`_)
+* ``-ObjC`` now correctly loads archives with Swift sections.
+  (`D125250 <https://reviews.llvm.org/D125250>`_)
+* ``-lto_object_path`` now accepts a filename (instead of just a directory
+  name.) (`D129705 <https://reviews.llvm.org/D129705>`_)
+* The ``LC_UUID`` hash now includes the output file's name.
+  (`D122843 <https://reviews.llvm.org/D122843>`_)
+* ``-flat_namespace`` now correctly makes all extern symbols in a dylib
+  interposable. (`D119294 <https://reviews.llvm.org/D119294>`_)
+* Fixed compact unwind output when linking on 32-bit hosts.
+  (`D129363 <https://reviews.llvm.org/D129363>`_)
+* Exporting private symbols no longer triggers an assertion.
+  (`D124143 <https://reviews.llvm.org/D124143>`_)
+* MacOS-only ``.tbd`` files are now supported when targeting Catalyst.
+  (`D124336 <https://reviews.llvm.org/D124336>`_)
+* Thunk symbols now have local visibility, avoiding false duplicate symbol
+  errors. (`D122624 <https://reviews.llvm.org/D122624>`_)
+* Fixed handling of relocatable object files within frameworks.
+  (`D114841 <https://reviews.llvm.org/D114841>`_)
+
 WebAssembly Improvements
 ------------------------