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

[Guo Ren]

On Mon, Jul 31, 2023 at 11:06 PM Mingzheng Xing
<xingmingzheng@xxxxxxxxxxx> 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@xxxxxxxxxx
> Link: https://lore.kernel.org/all/20230223220546.52879-1-conor@xxxxxxxxxx
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Mingzheng Xing <xingmingzheng@xxxxxxxxxxx>
> ---
>  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=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
> -       depends on 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.
> +       # https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd
> +       depends on AS_IS_GNU && AS_VERSION >= 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 extension to
> +         the Zicsr and Zifencei extensions. This requires explicitly specifying
> +         Zicsr and Zifencei when binutils >= 2.38 or GCC >= 12.1.0. Zicsr
> +         and Zifencei are supported in binutils from version 2.36 onwards.
> +         To make life easier, and avoid forcing toolchains that default to a
> +         newer ISA spec to version 2.2, relax the check to binutils >= 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/22e199e6afb1263c943c0c0d4498694e15bf8a16
> -       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. This
> -         option causes an older ISA spec compatible with these older versions
> -         of clang to be passed to GAS, which has the same result as passing zicsr
> -         and zifencei to -march.
> +       # https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b03be74bad08c382da47e048007a78fa3fb4ef49
> +       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 zifencei via
> +         -march. This option causes an older ISA spec compatible with these older
> +         versions of clang and GCC to be passed to GAS, which has the same 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/compat_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 += flush_icache
>  COMPAT_CC := $(CC)
>  COMPAT_LD := $(LD)
>
> -COMPAT_CC_FLAGS := -march=rv32g -mabi=ilp32
> +# 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@xxxxxxxxxx>

> +       COMPAT_CC_FLAGS := -march=rv32g -mabi=ilp32
> +else
> +       COMPAT_CC_FLAGS := -march=rv32imafd -mabi=ilp32
> +endif


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


-- 
Best Regards
 Guo Ren