linux-kernel - Re: [PATCH 06/10] powerpc: remove GCC version check for UPD

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Date:   Sat, 11 Sep 2021 20:43:57 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR

Nathan Chancellor <nathan@...nel.org> writes:
> On 9/10/2021 4:40 PM, Nick Desaulniers wrote:
>> Now that GCC 5.1 is the minimum supported version, we can drop this
>> workaround for older versions of GCC. This adversely affected clang,
>> too.
>> 
>> Cc: Michael Ellerman <mpe@...erman.id.au>
>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>> Cc: Paul Mackerras <paulus@...ba.org>
>> Cc: Segher Boessenkool <segher@...nel.crashing.org>
>> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
>> Cc: linuxppc-dev@...ts.ozlabs.org
>> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
>> ---
>>   arch/powerpc/include/asm/asm-const.h | 10 ----------
>>   1 file changed, 10 deletions(-)
>> 
>> diff --git a/arch/powerpc/include/asm/asm-const.h b/arch/powerpc/include/asm/asm-const.h
>> index 0ce2368bd20f..dbfa5e1e3198 100644
>> --- a/arch/powerpc/include/asm/asm-const.h
>> +++ b/arch/powerpc/include/asm/asm-const.h
>> @@ -12,16 +12,6 @@
>>   #  define ASM_CONST(x)		__ASM_CONST(x)
>>   #endif
>>   
>> -/*
>> - * Inline assembly memory constraint
>> - *
>> - * GCC 4.9 doesn't properly handle pre update memory constraint "m<>"
>> - *
>> - */
>> -#if defined(GCC_VERSION) && GCC_VERSION < 50000
>> -#define UPD_CONSTR ""
>> -#else
>>   #define UPD_CONSTR "<>"
>> -#endif
>
> The only reason this exists is because of commit 592bbe9c505d 
> ("powerpc/uaccess: Don't use "m<>" constraint with GCC 4.9"). It is 
> probably just worth sinking "<>" into all of the callsites and removing
> UPD_CONSTR.

Yeah that would be great if you're doing a v2. Or we can do it as a
follow-up.

cheers