llvm dev - Sep 2020 - binutils extensions: (1) dependency list in .a (2) SHF_GNU_RETAIN for GC roots in linking

I have recently seen two GNU binutils/GNU ABI extensions on binutils at
sourceware.org
They may potentially affect LLD and LLVM binary utilities, so I bring them
to your attention:)

https://sourceware.org/pipermail/binutils/2020-September/

(1) "dependency list for static libraries  "
   This adds a special member __.LIBDEP to an archive to represent
   something similar to DT_NEEDED in a shared object.

   This currently affects ar. ld is supposed to be affected but there is
   no patch yet. This may affect llvm-ar and LLD.

   I have one reply at
https://sourceware.org/pipermail/binutils/2020-September/113444.html
   You can click "Next message" to get the author's response.

(2) "[PATCH] Support SHF_GNU_RETAIN ELF section flag" and
     "[PATCH v2] Support for SHF_GNU_RETAIN ELF Section Flag"

   Basically, add a new section flag from SHF_MASKOS bits to express that
   a section has GC root semantics (ld --gc-sections).
   People mentioned GCC __attribute__((used)) could use this and the
   author appears to be working on it (but a reply says that the frontend
   feature do not need to hold up this proposal, so there is risk that it
   is committed before the design is done).

   This may affect Clang, LLVM's integrated assembler and LLD.

   I have one reply at
https://sourceware.org/pipermail/binutils/2020-September/113527.html
   (main points: (a) there are several alternative forms, e.g. SHT_GROUP, a
   new SHT_* for GC root (b) the way they design the new section flag
   adds one exception to "gas: error for section type, attr, or entsize
   change")


Many people may not be subscribed to binutils at sourceware.org
If you want to reply with proper In-Reply-To: , you can get Message-ID:
from https://sourceware.org/pipermail/binutils/2020-September.txt.gz
Though I think you may simply reply with Re: $original_subject

Updates:

On 2020-09-29, Fangrui Song wrote:
>I have recently seen two GNU binutils/GNU ABI extensions on binutils at
sourceware.org
>They may potentially affect LLD and LLVM binary utilities, so I bring them
>to your attention:)
>
>https://sourceware.org/pipermail/binutils/2020-September/
>
>(1) "dependency list for static libraries  "
>  This adds a special member __.LIBDEP to an archive to represent
>  something similar to DT_NEEDED in a shared object.
>
>  This currently affects ar. ld is supposed to be affected but there is
>  no patch yet. This may affect llvm-ar and LLD.
>
>  I have one reply at
https://sourceware.org/pipermail/binutils/2020-September/113444.html
>  You can click "Next message" to get the author's response.
Peter Smith shared some concerns as well. Still, GNU ar has adopted the change
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f3016d6ce178b76002edde12c30ebe7f608a8e21

The next step is a GNU ld change. If some packages start to adopt the feature,
it can impose some compatibility burden on llvm-ar and LLD as well. If you want
to comment on the thread "dependency list for static libraries"
(https://sourceware.org/pipermail/binutils/2020-November/113997.html), you can
use this tag:

   In-Reply-To: <7b118db2-9502-c45e-9f47-6b6f6a5f9646 at symas.com>
>(2) "[PATCH] Support SHF_GNU_RETAIN ELF section flag" and
>    "[PATCH v2] Support for SHF_GNU_RETAIN ELF Section Flag"
>
>  Basically, add a new section flag from SHF_MASKOS bits to express that
>  a section has GC root semantics (ld --gc-sections).
>  People mentioned GCC __attribute__((used)) could use this and the
>  author appears to be working on it (but a reply says that the frontend
>  feature do not need to hold up this proposal, so there is risk that it
>  is committed before the design is done).
>
>  This may affect Clang, LLVM's integrated assembler and LLD.
>
>  I have one reply at
https://sourceware.org/pipermail/binutils/2020-September/113527.html
>  (main points: (a) there are several alternative forms, e.g. SHT_GROUP, a
>  new SHT_* for GC root (b) the way they design the new section flag
>  adds one exception to "gas: error for section type, attr, or entsize
>  change")
This appears to receive good feedback and is likely to be accepted in GNU as
and ld. I personally have no issue with supporting it in LLVM's integrated
assembler and LLD.

There is still a dispute on the assembler directives (`.retain`), though:
https://sourceware.org/pipermail/binutils/2020-November/113993.html (and its
replies).