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Date:   Thu, 27 Jul 2023 00:48:28 +0800
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From:   Mingzheng Xing <xingmingzheng@iscas.ac.cn>
Subject: Re: [PATCH] riscv: Handle zicsr/zifencei issue between gcc and
 binutils
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        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
References: <20230725170405.251011-1-xingmingzheng@iscas.ac.cn>
 <20230725172344.GA1445373@dev-arch.thelio-3990X>
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On 7/26/23 01:23, Nathan Chancellor wrote:
> Hi Mingzheng,
>
> Thanks for the patch!
>
> On Wed, Jul 26, 2023 at 01:04:05AM +0800, Mingzheng Xing wrote:
>> When compiling the kernel with the toolchain composed of GCC >= 12.1.0 and
>> binutils < 2.38, default ISA spec used when building binutils and GCC, the
>> following build failure will appear because the
>> CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI is not turned on.
>> (i.e, gcc-12.1.0 and binutils-2.36, or gcc-12.3.0 and binutils-2.37, use
>> default ISA spec.)
>>
>>    CC      arch/riscv/kernel/vdso/vgettimeofday.o
>>    <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h: Assembler messages:
>>    <<BUILDDIR>>/arch/riscv/include/asm/vdso/gettimeofday.h:79: Error: unrecognized opcode `csrr a5,0xc01'
> The gift that keeps on giving :/
Yeah, but things will get better :)
>> Binutils has updated the default ISA spec version, and the community has
>> responded well to this[1][2][3], but it appears that this is not over yet.
>>
>> We also need to consider the situation of binutils < 2.38 but
>> GCC >= 12.1.0, since the combination between different versions of GCC and
>> binutils is not unique, which is to some extent flexible. GCC release
>> 12.1.0 updated the default ISA spec version in GCC commit[4].
> I suspect this combination is not too common because binutils 2.38 came
> out before GCC 12.1.0 but as you note, it is obviously possible. What
> toolchain has this combination in the wild, which would be helpful for
> documentation purposes?
Actually, this issue was discovered during the upgrade of the distribution
openEuler for RISC-V. It is a temporary phenomenon caused by
inconsistent upgrade speeds of packages such as GCC and binutils.
 From my limited understanding, GCC and binutils are not strictly
version-bound in some other distributions, so I can't rule out this issue
happening in other scenarios. But once it happens it can cause problems
with compiling the kernel.
>> 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")
>>
>> [1]:https://groups.google.com/a/groups.riscv.org/g/sw-dev/c/aE1ZeHHCYf4
>> [2]:https://lore.kernel.org/all/20230308220842.1231003-1-conor@kernel.org
>> [3]:https://lore.kernel.org/all/20230223220546.52879-1-conor@kernel.org
>> [4]:https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd
>>
>> Signed-off-by: Mingzheng Xing<xingmingzheng@iscas.ac.cn>
>> ---
>>   arch/riscv/Kconfig | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 4c07b9189c86..b49cea30f6cc 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -570,11 +570,15 @@ 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 CC_IS_GCC && GCC_VERSION >= 120100 || \
>> +		   AS_IS_GNU && AS_VERSION >= 23800
> GCC_VERSION will be 0 for clang, so you don't need the CC_IS_GCC check.
> With that change, this should be able to stay on one line:
>
>      depends on GCC_VERSION >= 120100 || (AS_IS_GNU && AS_VERSION >= 23800)
OK, I'll change it in v2.

Thanks,
Mingzheng.
>>   	help
>>   	  Newer binutils versions default to ISA spec version 20191213 which
>>   	  moves some instructions from the I extension to the Zicsr and Zifencei
>>   	  extensions.
>> +	  Similarly, GCC release 12.1.0 has changed the default ISA spec version to
>> +	  20191213, so the above situation requires this option to be enabled.
>>   
>>   config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
>>   	def_bool y
>> -- 
>> 2.34.1
>>
> Cheers,
> Nathan
>
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