Re: [PATCH v2] riscv: Handle zicsr/zifencei issue between gcc and binutils

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On 7/27/23 02:02, Conor Dooley wrote:
On Thu, Jul 27, 2023 at 01:45:24AM +0800, Mingzheng Xing wrote:
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
Can you provide a link to explain why this is 11.1.0 in particular?

Okay, I can add it in commit message. gcc-11.1.0 is particular
because it add support zicsr and zifencei extension for -march[1].

Link: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b03be74bad08c382da47e048007a78fa3fb4ef49 [1]

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@xxxxxxxxxx [1]
Link: https://lore.kernel.org/all/20230223220546.52879-1-conor@xxxxxxxxxx [2]
Link: https://lore.kernel.org/all/20230725170405.251011-1-xingmingzheng@xxxxxxxxxxx
This shouldn't be here, you don't link to your old patches.

My bad, I will fix it.


Signed-off-by: Mingzheng Xing <xingmingzheng@xxxxxxxxxxx>
This is still broken for:
CONFIG_CLANG_VERSION=0
CONFIG_AS_IS_GNU=y
CONFIG_AS_VERSION=23500
CONFIG_LD_IS_BFD=y
CONFIG_LD_VERSION=23500

Do you mean that these CONFIG_* will cause kernel
compilation errors when paired with certain versions of GCC?
Or perhaps I misunderstood your meaning.


Please don't post a v2 while there is still ongoing discussion on the
v1. I'll try to reply here tomorrow with a diff you can fold in to fix
the problem.

Okay, thanks for your review.

Thanks,
Conor.

---

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


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