linux-kernel - [PATCH v2] riscv: Handle zicsr/zifencei issue between gcc and binutils

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Message-Id: <20230726174524.340952-1-xingmingzheng@iscas.ac.cn>
Date:   Thu, 27 Jul 2023 01:45:24 +0800
From:   Mingzheng Xing <xingmingzheng@...as.ac.cn>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>
Cc:     Bin Meng <bmeng@...ylab.org>, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        stable@...r.kernel.org, Mingzheng Xing <xingmingzheng@...as.ac.cn>
Subject: [PATCH v2] riscv: Handle zicsr/zifencei issue between gcc and binutils

Binutils-2.38 and GCC-12.1.0 bump[0] default ISA spec to newer version
20191213 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 turn on TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
to cope with the new changes.

The case of clang is special[1][2], where older clang versions (<17) need
to be rolled back to old ISA spec to fix it. And the less common case,
since older GCC versions (<11.1.0) did not support zicsr and zifencei
extension for -march, also requires a fallback to cope with it.

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://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd [0]
Link: https://lore.kernel.org/all/20230308220842.1231003-1-conor@kernel.org [1]
Link: https://lore.kernel.org/all/20230223220546.52879-1-conor@kernel.org [2]
Link: https://lore.kernel.org/all/20230725170405.251011-1-xingmingzheng@iscas.ac.cn
Signed-off-by: Mingzheng Xing <xingmingzheng@...as.ac.cn>
---

v2:
- Update the Kconfig help text and commit message.
- Add considerations for low version gcc case.

Sorry for the formatting error on my mailing list reply.

 arch/riscv/Kconfig | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 4c07b9189c86..08afd47de157 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -570,24 +570,27 @@ 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 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.
+	  Binutils-2.38 and GCC-12.1.0 bump default ISA spec to newer version
+	  20191213 which moves some instructions from the I extension to the
+	  Zicsr and Zifencei extensions.
 
 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
+	# 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 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
+	  Certain versions of clang (or GCC) 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.
+	  of clang (or GCC) to be passed to GAS, which has the same result as
+	  passing zicsr and zifencei to -march.
 
 config FPU
 	bool "FPU support"
-- 
2.34.1