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Subject: Re: [PATCH] mips: Do not include hi and lo in clobber list for R6
To:     Alexander Lobakin <alobakin@pm.me>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Paul Burton <paulburton@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
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From:   Romain Naour <romain.naour@gmail.com>
Message-ID: <1c379050-b9de-d3cf-fad6-9c0bf9d4b920@gmail.com>
Date:   Sat, 25 Jul 2020 16:51:56 +0200
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Hi Alexander,

Le 25/07/2020 à 16:32, Alexander Lobakin a écrit :
> Hi Romain,
> 
> From: Romain Naour <romain.naour@gmail.com>
> Date: Sat, 25 Jul 2020 15:25:33 +0200
> 
>> From [1]
>> "GCC 10 (PR 91233) won't silently allow registers that are not architecturally
>> available to be present in the clobber list anymore, resulting in build failure
>> for mips*r6 targets in form of:
>> ...
>> .../sysdep.h:146:2: error: the register ‘lo’ cannot be clobbered in ‘asm’ for the current target
>>   146 |  __asm__ volatile (      \
>>       |  ^~~~~~~
>>
>> This is because base R6 ISA doesn't define hi and lo registers w/o DSP extension.
>> This patch provides the alternative clobber list for r6 targets that won't include
>> those registers."
>>
>> Since kernel 5.4 and mips support for generic vDSO [2], the kernel fail to build
>> for mips r6 cpus with gcc 10 for the same reason as glibc.
>>
>> [1] https://sourceware.org/git/?p=glibc.git;a=commit;h=020b2a97bb15f807c0482f0faee2184ed05bcad8
>> [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=24640f233b466051ad3a5d2786d2951e43026c9d
>>
>> Signed-off-by: Romain Naour <romain.naour@gmail.com>
>> ---
>>  arch/mips/include/asm/vdso/gettimeofday.h | 45 +++++++++++++++++++++++
>>  1 file changed, 45 insertions(+)
>>
>> diff --git a/arch/mips/include/asm/vdso/gettimeofday.h b/arch/mips/include/asm/vdso/gettimeofday.h
>> index c63ddcaea54c..6192d94928b9 100644
>> --- a/arch/mips/include/asm/vdso/gettimeofday.h
>> +++ b/arch/mips/include/asm/vdso/gettimeofday.h
>> @@ -30,12 +30,21 @@ static __always_inline long gettimeofday_fallback(
>>  	register long nr asm("v0") = __NR_gettimeofday;
>>  	register long error asm("a3");
>>  
>> +#if __mips_isa_rev >= 6
> 
> You should use MIPS_ISA_REV macro from arch/mips/include/asm/isa-rev.h
> instead of compiler definitions.
> The main reason is that __mips_isa_rev is not defined by GCC for
> pre-MIPS32 processors, so you'll get a compiler warning like:
> 
> "Warning: macro '__mips_isa_rev' is not defined, evaluates to 0"
> 
> MIPS_ISA_REV handles this case and is always defined regardless of
> the actual ISA family.

Thanks for the review.
Fixed in v2.

Best regards,
Romain

> 
>> +	asm volatile(
>> +	"       syscall\n"
>> +	: "=r" (ret), "=r" (error)
>> +	: "r" (tv), "r" (tz), "r" (nr)
>> +	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>> +	  "$14", "$15", "$24", "$25", "memory");
>> +#else
>>  	asm volatile(
>>  	"       syscall\n"
>>  	: "=r" (ret), "=r" (error)
>>  	: "r" (tv), "r" (tz), "r" (nr)
>>  	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>>  	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
>> +#endif
>>  
>>  	return error ? -ret : ret;
>>  }
>> @@ -54,12 +63,21 @@ static __always_inline long clock_gettime_fallback(
>>  #endif
>>  	register long error asm("a3");
>>  
>> +#if __mips_isa_rev >= 6
>> +	asm volatile(
>> +	"       syscall\n"
>> +	: "=r" (ret), "=r" (error)
>> +	: "r" (clkid), "r" (ts), "r" (nr)
>> +	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>> +	  "$14", "$15", "$24", "$25", "memory");
>> +#else
>>  	asm volatile(
>>  	"       syscall\n"
>>  	: "=r" (ret), "=r" (error)
>>  	: "r" (clkid), "r" (ts), "r" (nr)
>>  	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>>  	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
>> +#endif
>>  
>>  	return error ? -ret : ret;
>>  }
>> @@ -78,12 +96,21 @@ static __always_inline int clock_getres_fallback(
>>  #endif
>>  	register long error asm("a3");
>>  
>> +#if __mips_isa_rev >= 6
>> +	asm volatile(
>> +	"       syscall\n"
>> +	: "=r" (ret), "=r" (error)
>> +	: "r" (clkid), "r" (ts), "r" (nr)
>> +	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>> +	  "$14", "$15", "$24", "$25", "memory");
>> +#else
>>  	asm volatile(
>>  	"       syscall\n"
>>  	: "=r" (ret), "=r" (error)
>>  	: "r" (clkid), "r" (ts), "r" (nr)
>>  	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>>  	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
>> +#endif
>>  
>>  	return error ? -ret : ret;
>>  }
>> @@ -100,12 +127,21 @@ static __always_inline long clock_gettime32_fallback(
>>  	register long nr asm("v0") = __NR_clock_gettime;
>>  	register long error asm("a3");
>>  
>> +#if __mips_isa_rev >= 6
>> +	asm volatile(
>> +	"       syscall\n"
>> +	: "=r" (ret), "=r" (error)
>> +	: "r" (clkid), "r" (ts), "r" (nr)
>> +	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>> +	  "$14", "$15", "$24", "$25", "memory");
>> +#else
>>  	asm volatile(
>>  	"       syscall\n"
>>  	: "=r" (ret), "=r" (error)
>>  	: "r" (clkid), "r" (ts), "r" (nr)
>>  	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>>  	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
>> +#endif
>>  
>>  	return error ? -ret : ret;
>>  }
>> @@ -120,12 +156,21 @@ static __always_inline int clock_getres32_fallback(
>>  	register long nr asm("v0") = __NR_clock_getres;
>>  	register long error asm("a3");
>>  
>> +#if __mips_isa_rev >= 6
>> +	asm volatile(
>> +	"       syscall\n"
>> +	: "=r" (ret), "=r" (error)
>> +	: "r" (clkid), "r" (ts), "r" (nr)
>> +	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>> +	  "$14", "$15", "$24", "$25", "memory");
>> +#else
>>  	asm volatile(
>>  	"       syscall\n"
>>  	: "=r" (ret), "=r" (error)
>>  	: "r" (clkid), "r" (ts), "r" (nr)
>>  	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
>>  	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
>> +#endif
>>  
>>  	return error ? -ret : ret;
>>  }
>> -- 
>> 2.25.4
>