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

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Date:   Tue, 25 Jul 2023 10:23:44 -0700
From:   Nathan Chancellor <nathan@...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>,
        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
Subject: Re: [PATCH] riscv: Handle zicsr/zifencei issue between gcc and
 binutils

Hi Mingzheng,

Thanks for the patch!

On Wed, Jul 26, 2023 at 01:04:05AM +0800, Mingzheng Xing wrote:
> When compiling the kernel with the toolchain composed of GCC >= 12.1.0 and
> binutils < 2.38, default ISA spec used when building binutils and GCC, the
> following build failure will appear because the
> CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI is not turned on.
> (i.e, gcc-12.1.0 and binutils-2.36, or gcc-12.3.0 and binutils-2.37, use
> default ISA spec.)
> 
>   CC      arch/riscv/kernel/vdso/vgettimeofday.o
>   <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h: Assembler messages:
>   <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:79: Error: unrecognized opcode `csrr a5,0xc01'

The gift that keeps on giving :/

> Binutils has updated the default ISA spec version, and the community has
> responded well to this[1][2][3], but it appears that this is not over yet.
> 
> We also need to consider the situation of binutils < 2.38 but
> GCC >= 12.1.0, since the combination between different versions of GCC and
> binutils is not unique, which is to some extent flexible. GCC release
> 12.1.0 updated the default ISA spec version in GCC commit[4].

I suspect this combination is not too common because binutils 2.38 came
out before GCC 12.1.0 but as you note, it is obviously possible. What
toolchain has this combination in the wild, which would be helpful for
documentation purposes?

> 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")
> 
> [1]: https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/aE1ZeHHCYf4
> [2]: https://lore.kernel.org/all/20230308220842.1231003-1-conor@kernel.org
> [3]: https://lore.kernel.org/all/20230223220546.52879-1-conor@kernel.org
> [4]: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd
> 
> Signed-off-by: Mingzheng Xing <xingmingzheng@...as.ac.cn>
> ---
>  arch/riscv/Kconfig | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 4c07b9189c86..b49cea30f6cc 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -570,11 +570,15 @@ config TOOLCHAIN_HAS_ZIHINTPAUSE
>  config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
>  	def_bool y
>  	# https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
> -	depends on AS_IS_GNU && AS_VERSION >= 23800
> +	# https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd
> +	depends on CC_IS_GCC && GCC_VERSION >= 120100 || \
> +		   AS_IS_GNU && AS_VERSION >= 23800

GCC_VERSION will be 0 for clang, so you don't need the CC_IS_GCC check.
With that change, this should be able to stay on one line:

    depends on GCC_VERSION >= 120100 || (AS_IS_GNU && AS_VERSION >= 23800)

>  	help
>  	  Newer binutils versions default to ISA spec version 20191213 which
>  	  moves some instructions from the I extension to the Zicsr and Zifencei
>  	  extensions.
> +	  Similarly, GCC release 12.1.0 has changed the default ISA spec version to
> +	  20191213, so the above situation requires this option to be enabled.
>  
>  config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
>  	def_bool y
> -- 
> 2.34.1
> 

Cheers,
Nathan