From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Arnd Bergmann <arnd@arndb.de>, Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org, Shuah Khan <shuah@kernel.org>,
linux-kernel@vger.kernel.org,
Dmitry Safonov <0x7f454c46@gmail.com>,
Huw Davies <huw@codeweavers.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Will Deacon <will.deacon@arm.com>,
linux-mips@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
Russell King <linux@armlinux.org.uk>,
clang-built-linux@googlegroups.com,
Paul Burton <paul.burton@mips.com>,
linux-kselftest@vger.kernel.org,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Mark Salyzyn <salyzyn@android.com>,
Peter Collingbourne <pcc@google.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] vsyscall: use __iter_div_u64_rem()
Date: Thu, 11 Jul 2019 13:14:39 +0100 [thread overview]
Message-ID: <33511b0e-6d7b-c156-c415-7a609b049567@arm.com> (raw)
In-Reply-To: <20190710130206.1670830-1-arnd@arndb.de>
Hi Arnd,
On 10/07/2019 14:01, 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);
>
I am trying to test this patch using clang-9 tip:
# clang -v
clang version 9.0.0 (git@github.com:llvm-mirror/clang.git
6ed0749151866894a67a3e7eefdc1f3a547daa0e) (git@github.com:llvm-mirror/llvm.git
a10a70238ace1093cad3adeb94814b422bd1b5c1)
but I get a lot of errors similar to the one below:
In file included from ~/linux/arch/x86/events/amd/core.c:11:
~/linux/arch/x86/events/amd/../perf_event.h:824:21: error: invalid output size
for constraint '=q'
u64 disable_mask = __this_cpu_read(cpu_hw_events.perf_ctr_virt_mask);
^
~/linux/include/linux/percpu-defs.h:447:2: note: expanded from macro
'__this_cpu_read'
raw_cpu_read(pcp); \
^
~/linux/include/linux/percpu-defs.h:421:28: note: expanded from macro 'raw_cpu_read'
#define raw_cpu_read(pcp) __pcpu_size_call_return(raw_cpu_read_, pcp)
^
~/linux/include/linux/percpu-defs.h:322:23: note: expanded from macro
'__pcpu_size_call_return'
case 1: pscr_ret__ = stem##1(variable); break; \
^
<scratch space>:110:1: note: expanded from here
raw_cpu_read_1
^
~/linux/arch/x86/include/asm/percpu.h:394:30: note: expanded from macro
'raw_cpu_read_1'
#define raw_cpu_read_1(pcp) percpu_from_op(, "mov", pcp)
^
~/linux/arch/x86/include/asm/percpu.h:189:15: note: expanded from macro
'percpu_from_op'
: "=q" (pfo_ret__) \
Could you please tell me which version of the compiler did you use?
My building command is:
# make mrproper && make CC=clang HOSTCC=clang i386_defconfig && make ARCH=i386
CC=clang HOSTCC=clang -j56
--
Regards,
Vincenzo
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next prev parent reply other threads:[~2019-07-11 12:14 UTC|newest]
Thread overview: 7+ 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 16:56 ` Nathan Chancellor
2019-07-11 12:14 ` Vincenzo Frascino [this message]
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
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