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Date: Sat, 25 Jul 2020 14:32:53 +0000
From: Alexander Lobakin <alobakin@...me>
To: Romain Naour <romain.naour@...il.com>
Cc: Alexander Lobakin <alobakin@...me>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Paul Burton <paulburton@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mips: Do not include hi and lo in clobber list for R6
Hi Romain,
From: Romain Naour <romain.naour@...il.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@...il.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.
> + 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
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