linux-kernel - Re: [PATCH 08/12] tools/nolibc: gettimeofday(): avoid libgcc 64-bit divisions

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Message-ID: <20251102083156.GA10797@1wt.eu>
Date: Sun, 2 Nov 2025 09:31:56 +0100
From: Willy Tarreau <w@....eu>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Shuah Khan <shuah@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 08/12] tools/nolibc: gettimeofday(): avoid libgcc 64-bit
 divisions

On Wed, Oct 29, 2025 at 05:02:58PM +0100, Thomas Weißschuh wrote:
> timespec::tv_nsec is going to be 64-bit wide even on 32-bit
> architectures. As not all architectures support 64-bit division
> instructions, calls to libgcc (__divdi3()) may be emitted by the
> compiler which are not provided by nolibc.
> 
> As tv_nsec is guaranteed to always fit into an uint32_t, perform a
> 32-bit division instead.
>
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  tools/include/nolibc/sys/time.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/include/nolibc/sys/time.h b/tools/include/nolibc/sys/time.h
> index 33782a19aae9..6dd3705c6c9d 100644
> --- a/tools/include/nolibc/sys/time.h
> +++ b/tools/include/nolibc/sys/time.h
> @@ -33,7 +33,7 @@ int sys_gettimeofday(struct timeval *tv, struct timezone *tz)
>  	ret = sys_clock_gettime(CLOCK_REALTIME, &tp);
>  	if (!ret && tv) {
>  		tv->tv_sec = tp.tv_sec;
> -		tv->tv_usec = tp.tv_nsec / 1000;
> +		tv->tv_usec = (uint32_t)tp.tv_nsec / 1000;
>  	}

Good catch! I'm wondering if this one shouldn't be marked as a build
fix for 5e7392dc82ed ("tools/nolibc: fall back to sys_clock_gettime()
in gettimeofday()") so that it can be backported.

Acked-by: Willy Tarreau <w@....eu>

Willy