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Message-ID: <CAJF2gTTDnqXKuEBGttN-1sJD9GH8Y5FLP2R5cpxnWnkfyqaFVA@mail.gmail.com>
Date: Mon, 16 May 2022 14:55:24 +0800
From: Guo Ren <guoren@...nel.org>
To: Heiko Stuebner <heiko@...ech.de>
Cc: Palmer Dabbelt <palmer@...belt.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Albert Ou <aou@...s.berkeley.edu>,
linux-riscv <linux-riscv@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Wei Fu <wefu@...hat.com>, liush <liush@...winnertech.com>,
Atish Patra <atishp@...shpatra.org>,
Anup Patel <anup@...infault.org>,
Drew Fustini <drew@...gleboard.org>,
Christoph Hellwig <hch@....de>, Arnd Bergmann <arnd@...db.de>,
Chen-Yu Tsai <wens@...e.org>,
Maxime Ripard <maxime@...no.tech>,
Greg Favor <gfavor@...tanamicro.com>,
Andrea Mondelli <andrea.mondelli@...wei.com>,
Jonathan Behrens <behrensj@....edu>,
"Xinhaoqu (Freddie)" <xinhaoqu@...wei.com>,
Nick Kossifidis <mick@....forth.gr>,
Allen Baum <allen.baum@...erantotech.com>,
Josh Scheid <jscheid@...tanamicro.com>,
Richard Trauben <rtrauben@...il.com>,
Samuel Holland <samuel@...lland.org>,
Christoph Muellner <cmuellner@...ux.com>,
Philipp Tomsich <philipp.tomsich@...ll.eu>
Subject: Re: [PATCH 06/12] riscv: prevent compressed instructions in alternatives
Reviewed-by: Guo Ren <guoren@...nel.org>
On Thu, May 12, 2022 at 3:29 AM Heiko Stuebner <heiko@...ech.de> wrote:
>
> Instructions are opportunistically compressed by the RISC-V assembler
> when possible, but in alternatives-blocks both the old and new content
> need to be the same size, so having the toolchain do somewhat random
> optimizations will cause strange side-effects like
> "attempt to move .org backwards" compile-time errors.
>
> Already a simple "and" used in alternatives assembly will cause these
> mismatched code sizes.
>
> So prevent compressed instructions to be generated in alternatives-
> code and use option-push and -pop to only limit this to the relevant
> code blocks
>
> Signed-off-by: Heiko Stuebner <heiko@...ech.de>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Philipp Tomsich <philipp.tomsich@...ll.eu>
> ---
> arch/riscv/include/asm/alternative-macros.h | 24 +++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/arch/riscv/include/asm/alternative-macros.h b/arch/riscv/include/asm/alternative-macros.h
> index 8c2bbc7bbe50..e13b1f6bb400 100644
> --- a/arch/riscv/include/asm/alternative-macros.h
> +++ b/arch/riscv/include/asm/alternative-macros.h
> @@ -21,7 +21,11 @@
> .popsection
> .subsection 1
> 888 :
> + .option push
> + .option norvc
> + .option norelax
> \new_c
> + .option pop
> 889 :
> .previous
> .org . - (889b - 888b) + (887b - 886b)
> @@ -31,7 +35,11 @@
>
> .macro __ALTERNATIVE_CFG old_c, new_c, vendor_id, errata_id, enable
> 886 :
> + .option push
> + .option norvc
> + .option norelax
> \old_c
> + .option pop
> 887 :
> ALT_NEW_CONTENT \vendor_id, \errata_id, \enable, \new_c
> .endm
> @@ -42,7 +50,11 @@
> .macro __ALTERNATIVE_CFG_2 old_c, new_c_1, vendor_id_1, errata_id_1, enable_1, \
> new_c_2, vendor_id_2, errata_id_2, enable_2
> 886 :
> + .option push
> + .option norvc
> + .option norelax
> \old_c
> + .option pop
> 887 :
> ALT_NEW_CONTENT \vendor_id_1, \errata_id_1, \enable_1, \new_c_1
> ALT_NEW_CONTENT \vendor_id_2, \errata_id_2, \enable_2, \new_c_2
> @@ -76,7 +88,11 @@
> ".popsection\n" \
> ".subsection 1\n" \
> "888 :\n" \
> + ".option push\n" \
> + ".option norvc\n" \
> + ".option norelax\n" \
> new_c "\n" \
> + ".option pop\n" \
> "889 :\n" \
> ".previous\n" \
> ".org . - (887b - 886b) + (889b - 888b)\n" \
> @@ -85,7 +101,11 @@
>
> #define __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, enable) \
> "886 :\n" \
> + ".option push\n" \
> + ".option norvc\n" \
> + ".option norelax\n" \
> old_c "\n" \
> + ".option pop\n" \
> "887 :\n" \
> ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c)
>
> @@ -97,7 +117,11 @@
> new_c_2, vendor_id_2, errata_id_2, \
> enable_2) \
> "886 :\n" \
> + ".option push\n" \
> + ".option norvc\n" \
> + ".option norelax\n" \
> old_c "\n" \
> + ".option pop\n" \
> "887 :\n" \
> ALT_NEW_CONTENT(vendor_id_1, errata_id_1, enable_1, new_c_1) \
> ALT_NEW_CONTENT(vendor_id_2, errata_id_2, enable_2, new_c_2)
> --
> 2.35.1
>
--
Best Regards
Guo Ren
ML: https://lore.kernel.org/linux-csky/
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