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Message-ID: <90d97914-9576-42e7-0d7d-c752b5bd6a68@iscas.ac.cn>
Date:   Mon, 31 Jul 2023 23:16:14 +0800
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Subject: Re: [PATCH v3] riscv: Handle zicsr/zifencei issue between gcc and
 binutils
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To:     Conor Dooley <conor.dooley@microchip.com>
Cc:     Conor Dooley <conor@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, Bin Meng <bmeng@tinylab.org>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, stable@vger.kernel.org,
        Guo Ren <guoren@kernel.org>
References: <20230731095936.23397-1-xingmingzheng@iscas.ac.cn>
 <20230731-calzone-gratified-dbc51639beec@wendy>
From:   Mingzheng Xing <xingmingzheng@iscas.ac.cn>
Organization: ISCAS
In-Reply-To: <20230731-calzone-gratified-dbc51639beec@wendy>
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On 7/31/23 22:01, Conor Dooley wrote:
> Hey,
>
> On Mon, Jul 31, 2023 at 05:59:36PM +0800, Mingzheng Xing wrote:
>> 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
>> Signed-off-by: Mingzheng Xing <xingmingzheng@iscas.ac.cn>
> You need to actually put the CC: stable@vger.kernel.org into the commit
> message for the stable folks to pick things up.

Thanks. Fixed in next version.

>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 4c07b9189c86..2704bd91dfb5 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -570,24 +570,31 @@ 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,
>> but this only
>> +	  occurs when binutils >= 2.36 and GCC >= 11.1.0.
>> +	 It's a different story when binutils < 2.36.
> I would replace this with something like:
> 	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.
>
> I tried to take the personification out of it & hopefully made it a
> little clearer what dropping the check to 2.36 does for us.
>
>> Also, we have to consider the case of clang paired with binutils.
> I think this sentence can go, its covered in the other config text.
>
> I'm sorry for being a bit of a pedant about this, but this has been such
> a can of worms that I would like things to remain explained well enough
> that the text is sufficient next time a revisit is required.

Thanks for your review, I've made the changes and submitted a
new PATCH but there seems to be an email thread issue,
hopefully it won't have an effect, sorry about that.

:)
Thanks,
Mingzheng.

>
> Thanks,
> Conor.
>
>> +	  To make our lives easier, we relax the check to binutils >= 2.36. >
>>   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
>>
>>
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