linux-kernel - Re: [PATCH 1/2] MIPS: Loongson64: Clean up use of cc-ifversion

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Message-Id: <c88b0d87-b238-4889-b033-226bed85bb01@www.fastmail.com>
Date:   Tue, 25 Jan 2022 00:03:32 +0000
From:   "Jiaxun Yang" <jiaxun.yang@...goat.com>
To:     "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>
Cc:     "Huacai Chen" <chenhuacai@...nel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 1/2] MIPS: Loongson64: Clean up use of cc-ifversion



在2022年1月24日一月 下午8:31，Nick Desaulniers写道：
> On Thu, Jan 20, 2022 at 1:40 PM Nathan Chancellor <nathan@...nel.org> wrote:
>>
>> This Makefile checks that GCC is 4.9 or newer, which is redundant after
>> commit 76ae847497bc ("Documentation: raise minimum supported version of
>> GCC to 5.1"), so cc-option can be removed.
>>
>> Clang does not support -march=loongson3a so it needs to continue to use
>> -march=mips64r2, along with binutils less than 2.25, so check that both
>> GCC and binutils 2.25 or newer are being used before using
>> -march=loongson3a. These flags do not need to be checked with cc-option
>> anymore because all GCC versions support -march=loongson3a and
>> -march=mips64r2 and all clang versions support -march=mips64r2.
>>
>> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
>
> Thanks for the patch. I wonder why `_MIPS_ISA` only seems to be set at
> all for `-march=loongson3a` AFAICT, though that question is orthogonal
> to this patch. Perhaps the Loongson or MIPS maintainers know more?
> Otherwise seems like most uses of _MIPS_ISA can either be deleted or
> simplified now.

This is because earlier GCC mistakenly set loongson3a to MIPS64 not MIPS64R2.

But given that it's earlier than the minimal requirement GCC of kernel today, I think it should be safe to just move the whole logic.

Thanks.

>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
>
>> ---
>>  arch/mips/loongson64/Platform | 13 +++----------
>>  1 file changed, 3 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/mips/loongson64/Platform b/arch/mips/loongson64/Platform
>> index 3e660d6d3c2b..981d3abc150e 100644
>> --- a/arch/mips/loongson64/Platform
>> +++ b/arch/mips/loongson64/Platform
>> @@ -12,17 +12,10 @@ cflags-$(CONFIG_CPU_LOONGSON64)     += -Wa,--trap
>>  # by GAS.  The cc-option can't probe for this behaviour so -march=loongson3a
>>  # can't easily be used safely within the kbuild framework.
>>  #
>> -ifeq ($(call cc-ifversion, -ge, 0409, y), y)
>> -  ifeq ($(call ld-ifversion, -ge, 22500, y), y)
>> -    cflags-$(CONFIG_CPU_LOONGSON64)  += \
>> -      $(call cc-option,-march=loongson3a -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
>> -  else
>> -    cflags-$(CONFIG_CPU_LOONGSON64)  += \
>> -      $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
>> -  endif
>> +ifeq ($(CONFIG_CC_IS_GCC)$(call ld-ifversion, -ge, 22500, y), yy)
>> +  cflags-$(CONFIG_CPU_LOONGSON64) += -march=loongson3a -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64
>>  else
>> -    cflags-$(CONFIG_CPU_LOONGSON64)  += \
>> -      $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
>> +  cflags-$(CONFIG_CPU_LOONGSON64) += -march=mips64r2
>>  endif
>>
>>  # Some -march= flags enable MMI instructions, and GCC complains about that
>>
>> base-commit: 2c271fe77d52a0555161926c232cd5bc07178b39
>> --
>> 2.34.1
>>
>
>
> -- 
> Thanks,
> ~Nick Desaulniers

-- 
- Jiaxun