Re: [PATCH 06/12] riscv: prevent compressed instructions in alternatives

Guo Ren
2022-05-16T06:55:48Z

Reviewed-by: Guo Ren <guoren@kernel.org>

On Thu, May 12, 2022 at 3:29 AM Heiko Stuebner <heiko@sntech.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@sntech.de>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Philipp Tomsich <philipp.tomsich@vrull.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/