Re: [PATCH v3] riscv: Handle zicsr/zifencei issue between gcc and binutils

Hey,

On Mon, Jul 31, 2023 at 05:59:36PM +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%3Ba=commit%3Bh=aed44286efa8ae... [0] Link: https://gcc.gnu.org/git/?p=gcc.git%3Ba=commit%3Bh=98416dbb0a62579d4a7a4a76ba... [1] Link: https://sourceware.org/git/?p=binutils-gdb.git%3Ba=commit%3Bh=5a1b31e1e1cee6... [2] Link: https://sourceware.org/git/?p=binutils-gdb.git%3Ba=commit%3Bh=729a53530e8697... [3] Link: https://gcc.gnu.org/git/?p=gcc.git%3Ba=commit%3Bh=b03be74bad08c382da47e04800... [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 Signed-off-by: Mingzheng Xing xingmingzheng@iscas.ac.cn

You need to actually put the CC: stable@vger.kernel.org into the commit message for the stable folks to pick things up.

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 4c07b9189c86..2704bd91dfb5 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -570,24 +570,31 @@ config TOOLCHAIN_HAS_ZIHINTPAUSE config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI def_bool y # https://sourceware.org/git/?p=binutils-gdb.git%3Ba=commit%3Bh=aed44286efa8ae...

• 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%3Ba=commit%3Bh=98416dbb0a62579d4a7a4a76ba...
• 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,
  

but this only

•  occurs when binutils >= 2.36 and GCC >= 11.1.0.
  

• It's a different story when binutils < 2.36.
  

I would replace this with something like: 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.

I tried to take the personification out of it & hopefully made it a little clearer what dropping the check to 2.36 does for us.

Also, we have to consider the case of clang paired with binutils.

I think this sentence can go, its covered in the other config text.

I'm sorry for being a bit of a pedant about this, but this has been such a can of worms that I would like things to remain explained well enough that the text is sufficient next time a revisit is required.

Thanks, Conor.

•  To make our lives easier, we relax the check to binutils >= 2.36. >  
  

config TOOLCHAIN_NEEDS_OLD_ISA_SPEC def_bool y depends on TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI # https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e...

• 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%3Ba=commit%3Bh=b03be74bad08c382da47e04800...
• 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

• 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