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

[Mingzheng Xing]

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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