From: Segher Boessenkool <segher@kernel.crashing.org>
To: Alan Modra <amodra@gmail.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [RS6000] Power10 libffi fixes
Date: Tue, 22 Sep 2020 19:16:57 -0500 [thread overview]
Message-ID: <20200923001657.GQ28786@gate.crashing.org> (raw)
In-Reply-To: <20200922003011.GB5452@bubble.grove.modra.org>
Hi!
On Tue, Sep 22, 2020 at 10:00:11AM +0930, Alan Modra wrote:
> Power10 pc-relative code doesn't use or preserve r2 as a TOC pointer.
> That means calling between pc-relative and TOC using code can't be
> done without intervening linker stubs, and a call from TOC code to
> pc-relative code must have a nop after the bl in order to restore r2.
>
> Now the PowerPC libffi assembly code doesn't use r2 except for the
> implicit use when making calls back to C, ffi_closure_helper_LINUX64
> and ffi_prep_args64. So changing the assembly to interoperate with
> pc-relative code without stubs is easily done. Controlling that is a
> new built-in macro.
>
> Upstream libffi currently has a different patch applied to work around
> the power10 build failure. I'll post a delta for upstream.
> Bootstrapped and regression tested on power8, built for power10.
>
> gcc/
> * config/rs6000/rs6000-c.c (rs6000_target_modify_macros):
> Conditionally define __PCREL__.
Please do that as a separate (earlier) patch (because it *is*, and to
simplify backports, etc).
> libffi/
> * src/powerpc/linux64.S (ffi_call_LINUX64): Don't emit global
> entry when __PCREL__. Call using @notoc.
> (ffi_closure_LINUX64, ffi_go_closure_linux64): Likewise.
This is okay for trunk, and for backports (possibly expedited, talk
with Peter for what is wanted/needed for AT).
Thanks!
Segher
next prev parent reply other threads:[~2020-09-23 0:17 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 0:30 Alan Modra
2020-09-23 0:16 ` Segher Boessenkool [this message]
2020-09-24 3:41 ` Alan Modra
2020-09-24 5:39 ` Alan Modra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200923001657.GQ28786@gate.crashing.org \
--to=segher@kernel.crashing.org \
--cc=amodra@gmail.com \
--cc=gcc-patches@gcc.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).