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References: <20230731095534.22842-1-xingmingzheng@iscas.ac.cn> <20230731150511.38140-1-xingmingzheng@iscas.ac.cn>
In-Reply-To: <20230731150511.38140-1-xingmingzheng@iscas.ac.cn>
From:   Guo Ren <guoren@kernel.org>
Date:   Tue, 1 Aug 2023 18:59:45 +0800
Message-ID: <CAJF2gTQ75bFm+=dZBV1dijNv5h-kKuAYKHkakgq-seTS5BWOBw@mail.gmail.com>
Subject: Re: [PATCH] riscv: Handle zicsr/zifencei issue between gcc and binutils
To:     Mingzheng Xing <xingmingzheng@iscas.ac.cn>
Cc:     Conor Dooley <conor@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, Bin Meng <bmeng@tinylab.org>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, stable@vger.kernel.org
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On Mon, Jul 31, 2023 at 11:06=E2=80=AFPM Mingzheng Xing
<xingmingzheng@iscas.ac.cn> wrote:
>
> Binutils-2.38 and GCC-12.1.0 bumped[0][1] the default ISA spec to the new=
er
> 20191213 version which moves some instructions from the I extension to th=
e
> Zicsr and Zifencei extensions. So if one of the binutils and GCC exceeds
> that version, we should explicitly specifying Zicsr and Zifencei via -mar=
ch
> to cope with the new changes. but this only occurs when binutils >=3D 2.3=
6
> and GCC >=3D 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 >=3D 12.1.0.
>
> To make our lives easier, let's relax the check to binutils >=3D 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 a=
nd binutils")
> Link: https://sourceware.org/git/?p=3Dbinutils-gdb.git;a=3Dcommit;h=3Daed=
44286efa8ae8717a77d94b51ac3614e2ca6dc [0]
> Link: https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dcommit;h=3D98416dbb0a62579=
d4a7a4a76bab51b5b52fec2cd [1]
> Link: https://sourceware.org/git/?p=3Dbinutils-gdb.git;a=3Dcommit;h=3D5a1=
b31e1e1cee6e9f1c92abff59cdcfff0dddf30 [2]
> Link: https://sourceware.org/git/?p=3Dbinutils-gdb.git;a=3Dcommit;h=3D729=
a53530e86972d1143553a415db34e6e01d5d2 [3]
> Link: https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dcommit;h=3Db03be74bad08c38=
2da47e048007a78fa3fb4ef49 [4]
> Link: https://lore.kernel.org/all/20230308220842.1231003-1-conor@kernel.o=
rg
> Link: https://lore.kernel.org/all/20230223220546.52879-1-conor@kernel.org
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Mingzheng Xing <xingmingzheng@iscas.ac.cn>
> ---
>  arch/riscv/Kconfig                     | 32 +++++++++++++++-----------
>  arch/riscv/kernel/compat_vdso/Makefile |  8 ++++++-
>  2 files changed, 26 insertions(+), 14 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 4c07b9189c86..10e7a7ad175a 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -570,24 +570,30 @@ config TOOLCHAIN_HAS_ZIHINTPAUSE
>  config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
>         def_bool y
>         # https://sourceware.org/git/?p=3Dbinutils-gdb.git;a=3Dcommit;h=
=3Daed44286efa8ae8717a77d94b51ac3614e2ca6dc
> -       depends on AS_IS_GNU && AS_VERSION >=3D 23800
> -       help
> -         Newer binutils versions default to ISA spec version 20191213 wh=
ich
> -         moves some instructions from the I extension to the Zicsr and Z=
ifencei
> -         extensions.
> +       # https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dcommit;h=3D98416dbb0a6=
2579d4a7a4a76bab51b5b52fec2cd
> +       depends on AS_IS_GNU && AS_VERSION >=3D 23600
> +       help
> +         Binutils-2.38 and GCC-12.1.0 bumped the default ISA spec to the=
 newer
> +         20191213 version, which moves some instructions from the I exte=
nsion to
> +         the Zicsr and Zifencei extensions. This requires explicitly spe=
cifying
> +         Zicsr and Zifencei when binutils >=3D 2.38 or GCC >=3D 12.1.0. =
Zicsr
> +         and Zifencei are supported in binutils from version 2.36 onward=
s.
> +         To make life easier, and avoid forcing toolchains that default =
to a
> +         newer ISA spec to version 2.2, relax the check to binutils >=3D=
 2.36.
> +         For clang < 17 or GCC < 11.1.0, for which this is not possible,=
 this is
> +         dealt with in CONFIG_TOOLCHAIN_NEEDS_OLD_ISA_SPEC.
>
>  config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
>         def_bool y
>         depends on TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
>         # https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943=
c0c0d4498694e15bf8a16
> -       depends on CC_IS_CLANG && CLANG_VERSION < 170000
> -       help
> -         Certain versions of clang do not support zicsr and zifencei via=
 -march
> -         but newer versions of binutils require it for the reasons noted=
 in the
> -         help text of CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI. Th=
is
> -         option causes an older ISA spec compatible with these older ver=
sions
> -         of clang to be passed to GAS, which has the same result as pass=
ing zicsr
> -         and zifencei to -march.
> +       # https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dcommit;h=3Db03be74bad0=
8c382da47e048007a78fa3fb4ef49
> +       depends on (CC_IS_CLANG && CLANG_VERSION < 170000) || (CC_IS_GCC =
&& GCC_VERSION < 110100)
> +       help
> +         Certain versions of clang and GCC do not support zicsr and zife=
ncei via
> +         -march. This option causes an older ISA spec compatible with th=
ese older
> +         versions of clang and GCC to be passed to GAS, which has the sa=
me result
> +         as passing zicsr and zifencei to -march.
>
>  config FPU
>         bool "FPU support"
> diff --git a/arch/riscv/kernel/compat_vdso/Makefile b/arch/riscv/kernel/c=
ompat_vdso/Makefile
> index 189345773e7e..b86e5e2c3aea 100644
> --- a/arch/riscv/kernel/compat_vdso/Makefile
> +++ b/arch/riscv/kernel/compat_vdso/Makefile
> @@ -11,7 +11,13 @@ compat_vdso-syms +=3D flush_icache
>  COMPAT_CC :=3D $(CC)
>  COMPAT_LD :=3D $(LD)
>
> -COMPAT_CC_FLAGS :=3D -march=3Drv32g -mabi=3Dilp32
> +# binutils 2.35 does not support the zifencei extension, but in the ISA
> +# spec 20191213, G stands for IMAFD_ZICSR_ZIFENCEI.
> +ifdef CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
Acked-by: Guo Ren <guoren@kernel.org>

> +       COMPAT_CC_FLAGS :=3D -march=3Drv32g -mabi=3Dilp32
> +else
> +       COMPAT_CC_FLAGS :=3D -march=3Drv32imafd -mabi=3Dilp32
> +endif


>  COMPAT_LD_FLAGS :=3D -melf32lriscv
>
>  # Disable attributes, as they're useless and break the build.
> --
> 2.34.1
>


--=20
Best Regards
 Guo Ren