From: Peter Smith <Peter.Smith@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>
Cc: Stefan Agner <stefan@agner.ch>, Tony Lindgren <tony@atomide.com>,
Russell King <linux@armlinux.org.uk>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>, nd <nd@arm.com>
Subject: Re: [PATCH] ARM: OMAP2+: drop unnecessary adrl
Date: Thu, 2 Apr 2020 11:50:06 +0000 [thread overview]
Message-ID: <DBBPR08MB4823129E272220712B470716F8C60@DBBPR08MB4823.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <CAMj1kXGYiMobkue642iDRdOjEHQK=KXpp=Urrgik9UU-eWWibQ@mail.gmail.com>
> I take it this implies that the LLVM linker does not support the
> R_ARM_ALU_PC_Gn relocations? Since otherwise, adrl could simply be
> expanded to a pair of adds with the appropriate relocations, letting
> the linker fix up the immediates (and the ADD vs SUB bits)
Not at the moment. I have a patch in review to add the G0 variants for these in Arm state at reviews.llvm.org/D75349 . As far as I know LLVM MC does not have support for generating the relocations either. This could be added though. I agree that using the G* relocations with a pair of add/sub instructions would be the ideal solution. The adrl psuedo is essentially that but implemented at assembly time. I think it would be possible to implement in LLVM but at the time (4+ years ago) I wasn't confident in finding someone that would think that adrl support was worth the disruption, for example the current Arm assembly backend can only produce 1 instruction as output and adrl requires two.
I'd be happy to look at group relocation support in LLD, I haven't got a lot of spare time so progress is likely to be slow though.
Peter
next prev parent reply other threads:[~2020-04-02 11:50 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-29 20:33 [PATCH] ARM: OMAP2+: drop unnecessary adrl Stefan Agner
2020-04-01 18:02 ` Nick Desaulniers
2020-04-02 9:48 ` Ard Biesheuvel
2020-04-02 11:50 ` Peter Smith [this message]
2020-04-02 12:05 ` Ard Biesheuvel
2020-04-02 14:34 ` Stefan Agner
2020-04-02 14:36 ` Ard Biesheuvel
2020-04-17 15:23 ` Tony Lindgren
2020-04-02 17:50 ` Peter Smith
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