[lld][ELF] Add some release notes

[MaskRay]

Summary

Based on release/10.x

[MaskRay]

Mention -Ttext=0

[atanasyan]

lld/docs/ReleaseNotes.rst

39

Why did you remove this line?

[MaskRay]

Add more items

[MaskRay]

lld/docs/ReleaseNotes.rst

39

IIUC, you meant https://reviews.llvm.org/rL371554.

But this size optimization is generic. It also removes upto 3*maxpagesize for other targets.

For example, defaultMaxPageSize is also 65536 on AArch64/powerpc32/powerpc64.

[MaskRay]

lld/docs/ReleaseNotes.rst

107

Range extension thunks with addens are implemented for AArch64, PowerPC32 and PowerPC64.

@atanasyan It'd be nice to fix this for MIPS as well, or make it clear that MIPS does not need it.

[MaskRay]

lld/docs/ReleaseNotes.rst

95

@psmith Maybe you can find ARM contacts who are concerned about this matter.
I believe PT_GNU_PROPERTY in binutils/glibc is not going well. https://sourceware.org/ml/binutils/2020-02/msg00512.html

[grimar]

lld/docs/ReleaseNotes.rst

80–91

Seems you're missing empty lines between improvements.

[atanasyan]

lld/docs/ReleaseNotes.rst

39

I agree that this change is generic. Does it make a sense to mention about it in the release notes in a generic form?

107

MIPS does not use range extension thunks.

[hans]

lld/docs/ReleaseNotes.rst

99

I think this note is too small for something that's clearly a breaking change for some projects. Could it be lifted out into a "breaking changes" section, with the migration information clearly laid out?

102

Ditto.

[psmith]

Thanks for taking the lead on this. I've put a few suggestions for some cosmetic changes.

lld/docs/ReleaseNotes.rst

80–91

I suggest "with a" rather than "of a".
For certain "undefined symbol" errors, a definition with a close spelling will be suggested.

87

I suggest "3 times maxpagesize." as 3 maxpagesizes isn't the name of an option.

95

Thanks for pointing that out. The request to add PT_GNU_PROPERTY came from the Android team as the kernel required PT_GNU_PROPERTY. I'll mention it to them.

107

typo: "with addends"

113

Suggest no longer, as it more strongly implies a change.
The ARM port will no longer insert interworking thunks for non STT_FUNC symbols.

115

Insert

• The ARM port will no longer interwork via changing a BL to a BLX for non STT_FUNC symbols. A warning will be given if this results in a change from previous LLD releases.

(D73542 <https://reviews.llvm.org/D73542_)

[MaskRay]

Address comments

lld/docs/ReleaseNotes.rst

39

It is covered by the -z noseparate-code item below.

115

D73542 is not in the release/10.x branch.

@psmith I think it makes sense to cherry pick https://reviews.llvm.org/rG29c13615576b80129c8167df1d77f1ce98a97ae7 to release/10.x . Is that your intention?

[psmith]

lld/docs/ReleaseNotes.rst

115

Sorry, my mistake. Yes you are correct, I'm not intending for that to be cherry-picked.

[hans]

lld/docs/ReleaseNotes.rst

84

Can you please put the migration information here in the notes instead?

[MaskRay]

lld/docs/ReleaseNotes.rst

84

Where should I write the notes?

[hans]

lld/docs/ReleaseNotes.rst

84

Right here :-)

``-Ttext=0`` is no longer supported. (See PRxxx)
This is how to deal with it: ...

[MaskRay]

Reword -Ttext=0

[hans]

Thanks!

[MaskRay]

Closed by release/10.x commit e705da06e22b12ee5d75076a2a1ae7b479a566e1

lld/docs/ReleaseNotes.rst

* Glob pattern, which you can use in linker scripts or version scripts,
   with GNU now. (`r375051
   <https://github.com/llvm/llvm-project/commit/48993d5ab9413f0e5b94dfa292a233ce55b09e3e>`_)
 
 * New ``elf32btsmipn32_fbsd`` and ``elf32ltsmipn32_fbsd`` emulations
   are supported.
 
 * Relax MIPS ``jalr``and ``jr`` instructions marked by the ``R_MIPS_JALR``
   relocation.
+* For certain "undefined symbol" errors, a definition with a close spelling will be suggested.
+  (`D67039 <https://reviews.llvm.org/D67039>`_)
+* ``extern "C"`` is suggested if an undefined reference is mangled(unmangled) while there
+  is a likely unmangled(mangled) definition.
+  (`D69592 <https://reviews.llvm.org/D69592>`_ `D69650 <https://reviews.llvm.org/D69650>`_)
+* New ``-z noseparate-code``, ``-z separate-code`` and ``-z separate-loadable-segments``.
+  ``-z noseparate-code`` is the default, which can reduce sizes of linked binaries by up to
+  3 times maxpagesize.
+  (`D64903 <https://reviews.llvm.org/D64903>`_ `D67481 <https://reviews.llvm.org/D67481>`_)
+* ``-z force-bti`` and ``-z pac-plt`` are added for AArch64 Branch Target Identification and Pointer Authentication.
+  (`D62609 <https://reviews.llvm.org/D62609>`_)
+* ``--fix-cortex-a8`` is added to fix erratum 657417.
+  (`D67284 <https://reviews.llvm.org/D67284>`_)
+* ``-z force-ibt`` and ``-z shstk`` are added for Intel Control-flow Enforcement Technology.
+  (`D59780 <https://reviews.llvm.org/D59780>`_)
+* ``PT_GNU_PROPERTY`` is added to help loaders locate the ``.note.gnu.property`` section.
+  It may be used by a future Linux kernel.
+  (`D70961 <https://reviews.llvm.org/D70961>`_)
+* For ``--compress-debug-sections=zlib``, ``-O0`` and ``-O1`` enable compression level 1
+  while ``-O2`` enables compression level 6. ``-O1`` (default) is faster than before.
+  (`D70658 <https://reviews.llvm.org/D70658>`_)
+* Range extension thunks with addends are implemented for AArch64, PowerPC32 and PowerPC64.
+  (`D70637 <https://reviews.llvm.org/D70637>`_ `D70937 <https://reviews.llvm.org/D70937>`_
+  `D73424 <https://reviews.llvm.org/D73424>`_)
+* ``R_RISCV_ALIGN`` will be errored because linker relaxation for RISC-V is not supported.
+  Pass ``-mno-relax`` to disable ``R_RISCV_ALIGN``.
+  (`D71820 <https://reviews.llvm.org/D71820>`_)
+* The ARM port will no longer insert interworking thunks for non STT_FUNC symbols.
+  (`D73474 <https://reviews.llvm.org/D73474>`_)
+* The quality of PowerPC32 port has been greatly improved (canonical PLT, copy
+  relocations, non-preemptible IFUNC, range extension thunks with addends).
+  It can link FreeBSD 13.0 userland.
+* The PowerPC64 port supports non-preemptible IFUNC.
+  (`D71509 <https://reviews.llvm.org/D71509>`_)
+* lld creates a RO PT_LOAD and a RX PT_LOAD without a linker script.
+  lld creates a unified RX PT_LOAD with a linker script.
+  A future release will eliminate this difference and use a RO PT_LOAD and a RX PT_LOAD by default.
+  The linker script case will require ``--no-rosegment`` to restore the current behavior.
+* GNU style compressed debug sections ``.zdebug`` (obsoleted by ``SHF_COMPRESSED``)
+  are supported for input files, but not for the output.
+  A future release may drop ``.zdebug`` support.
 
-* Reduced size of linked MIPS binaries.
+Breaking changes
+----------------
+
+* ``-Ttext=$base`` (base is usually 0) is no longer supported.
+  If PT_PHDR is needed, use ``--image-base=$base`` instead.
+  If PT_PHDR is not needed, use a linker script with `.text 0 : { *(.text*) }` as the first
+  output section description.
+  See https://bugs.llvm.org/show_bug.cgi?id=44715 for more information.
+  (`D67325 <https://reviews.llvm.org/D67325>`_)
+* ``-Ttext-segment`` is no longer supported. Its meaning was different from GNU ld's and
+  could cause subtle bugs.
+  (`D70468 <https://reviews.llvm.org/D70468>`_)
 
 COFF Improvements
 -----------------
 
 * ...
 
 MinGW Improvements
 ------------------
 
 * Allow using custom .edata sections from input object files (for use
   by Wine)
   (`dadc6f248868 <https://reviews.llvm.org/rGdadc6f248868>`)
 
 * Don't implicitly create import libraries unless requested
   (`6540e55067e3 <https://reviews.llvm.org/rG6540e55067e3>`)
 
 * Support merging multiple resource object files
   (`3d3a9b3b413d <https://reviews.llvm.org/rG3d3a9b3b413d>`)
   and properly handle the default manifest object files that GCC can pass
   (`d581dd501381 <https://reviews.llvm.org/rGd581dd501381>`)
 
 * Demangle itanium symbol names in warnings/error messages
   (`a66fc1c99f3e <https://reviews.llvm.org/rGa66fc1c99f3e>`)
 
 * Print source locations for undefined references and duplicate symbols,
   if possible
   (`1d06d48bb346 <https://reviews.llvm.org/rG1d06d48bb346>`)
   and
   (`b38f577c015c <https://reviews.llvm.org/rGb38f577c015c>`)
 
 * Look for more filename patterns when resolving ``-l`` options
   (`0226c35262df <https://reviews.llvm.org/rG0226c35262df>`)