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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251102094951.GB26041@1wt.eu>
Date: Sun, 2 Nov 2025 10:49:51 +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 Sun, Nov 02, 2025 at 10:27:18AM +0100, Thomas Weißschuh wrote:
> On 2025-11-02 09:31:56+0100, Willy Tarreau wrote:
> > 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.
> 
> Right now timespec::tv_nsec is of type 'long', so it should only be
> 64-bits on architectures which have native 64-bit division instructions. 
> But marking it as fix shouldn't hurt either.

Ah yeah you're right. Don't bother with that then.

Thanks!
Willy