From: Nathan Chancellor <natechancellor@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-mips@vger.kernel.org, linux-kselftest@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Russell King <linux@armlinux.org.uk>,
Ralf Baechle <ralf@linux-mips.org>,
Paul Burton <paul.burton@mips.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Mark Salyzyn <salyzyn@android.com>,
Peter Collingbourne <pcc@google.com>,
Shuah Khan <shuah@kernel.org>,
Dmitry Safonov <0x7f454c46@gmail.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Huw Davies <huw@codeweavers.com>,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH] vsyscall: use __iter_div_u64_rem()
Date: Wed, 10 Jul 2019 09:56:51 -0700 [thread overview]
Message-ID: <20190710165651.GA29814@archlinux-threadripper> (raw)
In-Reply-To: <20190710130206.1670830-1-arnd@arndb.de>
On Wed, Jul 10, 2019 at 03:01:53PM +0200, Arnd Bergmann wrote:
> On 32-bit x86 when building with clang-9, the loop gets turned back into
> an inefficient division that causes a link error:
>
> kernel/time/vsyscall.o: In function `update_vsyscall':
> vsyscall.c:(.text+0xe3): undefined reference to `__udivdi3'
>
> Use the provided __iter_div_u64_rem() function that is meant to address
> the same case in other files.
>
> Fixes: 44f57d788e7d ("timekeeping: Provide a generic update_vsyscall() implementation")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> kernel/time/vsyscall.c | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
> index a80893180826..8cf3596a4ce6 100644
> --- a/kernel/time/vsyscall.c
> +++ b/kernel/time/vsyscall.c
> @@ -104,11 +104,7 @@ void update_vsyscall(struct timekeeper *tk)
> vdso_ts->sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec;
> nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;
> nsec = nsec + tk->wall_to_monotonic.tv_nsec;
> - while (nsec >= NSEC_PER_SEC) {
> - nsec = nsec - NSEC_PER_SEC;
> - vdso_ts->sec++;
> - }
> - vdso_ts->nsec = nsec;
> + vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &vdso_ts->nsec);
>
> if (__arch_use_vsyscall(vdata))
> update_vdso_data(vdata, tk);
> --
> 2.20.0
>
What an interesting function. Looks good to me and I can confirm it
fixes the link error.
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
next prev parent reply other threads:[~2019-07-10 16:56 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-10 13:01 [PATCH] vsyscall: use __iter_div_u64_rem() Arnd Bergmann
2019-07-10 15:22 ` [tip:timers/urgent] timekeeping/vsyscall: Use __iter_div_u64_rem() tip-bot for Arnd Bergmann
2019-07-10 16:56 ` Nathan Chancellor [this message]
2019-07-10 18:43 ` tip-bot for Arnd Bergmann
2019-07-11 12:14 ` [PATCH] vsyscall: use __iter_div_u64_rem() Vincenzo Frascino
2019-07-11 12:28 ` Arnd Bergmann
2019-07-11 13:08 ` Vincenzo Frascino
2019-07-11 17:14 ` Nick Desaulniers
2019-07-11 20:55 ` Arnd Bergmann
2019-07-22 10:10 ` Thomas Gleixner
2019-07-22 10:38 ` Jan Beulich
2019-07-22 10:48 ` Arnd Bergmann
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