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

On Mon, Jul 31, 2023 at 11:06 PM Mingzheng Xing xingmingzheng@iscas.ac.cn 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 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=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;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/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;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@kernel.org

•   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