linux-kernel - Re: [PATCH] riscv: Handle zicsr/zifencei issue between gcc and binutils

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Message-ID: <20230731-legume-commend-9aafd84c1fb2@spud>
Date:   Mon, 31 Jul 2023 16:24:59 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Mingzheng Xing <xingmingzheng@...as.ac.cn>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, Bin Meng <bmeng@...ylab.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, stable@...r.kernel.org,
        Guo Ren <guoren@...nel.org>
Subject: Re: [PATCH] riscv: Handle zicsr/zifencei issue between gcc and
 binutils

On Mon, Jul 31, 2023 at 11:05:11PM +0800, Mingzheng Xing wrote:
> Binutils-2.38 and GCC-12.1.0 bumped[0][1] the default ISA spec to the newer
> 20191213 version which moves some instructions from the I extension to the
> Zicsr and Zifencei extensions. So if one of the binutils and GCC exceeds
> that version, we should explicitly specifying Zicsr and Zifencei via -march
> to cope with the new changes. but this only occurs when binutils >= 2.36
> and GCC >= 11.1.0. It's a different story when binutils < 2.36.
> 
> binutils-2.36 supports the Zifencei extension[2] and splits Zifencei and
> Zicsr from I[3]. GCC-11.1.0 is particular[4] because it add support Zicsr
> and Zifencei extension for -march. binutils-2.35 does not support the
> Zifencei extension, and does not need to specify Zicsr and Zifencei when
> working with GCC >= 12.1.0.
> 
> To make our lives easier, let's relax the check to binutils >= 2.36 in
> CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI. For the other two cases,
> where clang < 17 or GCC < 11.1.0, we will deal with them in
> CONFIG_TOOLCHAIN_NEEDS_OLD_ISA_SPEC.
> 
> For more information, please refer to:
> commit 6df2a016c0c8 ("riscv: fix build with binutils 2.38")
> commit e89c2e815e76 ("riscv: Handle zicsr/zifencei issues between clang and binutils")
> Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc [0]
> Link: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd [1]
> Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=5a1b31e1e1cee6e9f1c92abff59cdcfff0dddf30 [2]
> Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=729a53530e86972d1143553a415db34e6e01d5d2 [3]
> Link: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b03be74bad08c382da47e048007a78fa3fb4ef49 [4]
> Link: https://lore.kernel.org/all/20230308220842.1231003-1-conor@kernel.org
> Link: https://lore.kernel.org/all/20230223220546.52879-1-conor@kernel.org
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Mingzheng Xing <xingmingzheng@...as.ac.cn>

This looks good to me now, thanks! Hopefully the next time we look at
this code is removing support for binutils 2.35 :)
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

Cheers,
Conor.

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