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

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Date:   Thu, 27 Jul 2023 03:34:16 +0800
From:   Mingzheng Xing <xingmingzheng@...as.ac.cn>
To:     Conor Dooley <conor@...nel.org>
Cc:     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>, Bin Meng <bmeng@...ylab.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH v2] riscv: Handle zicsr/zifencei issue between gcc and
 binutils

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@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
> 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@...as.ac.cn>
> 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
>>
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv

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