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

[Mingzheng Xing]

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@kernel.org
Link: https://lore.kernel.org/all/20230223220546.52879-1-conor@kernel.org
Cc: <stable at vger.kernel.org>
Signed-off-by: Mingzheng Xing <xingmingzheng at 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;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
+	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