linux-kernel - Re: [PATCH 07/12] tools/nolibc: prefer explicit 64-bit time-related system calls

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Message-Id: <fbca1d3e-12e4-4c4e-8091-87464035fe39@app.fastmail.com>
Date: Thu, 30 Oct 2025 15:44:21 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: Thomas Weißschuh <linux@...ssschuh.net>,
 "Willy Tarreau" <w@....eu>, shuah <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 07/12] tools/nolibc: prefer explicit 64-bit time-related system
 calls

On Wed, Oct 29, 2025, at 17:02, Thomas Weißschuh wrote:
> Make sure to always use the 64-bit safe system calls
> in preparation for 64-bit time_t on 32-bit architectures.
>
> Also prevent issues on kernels which disable CONFIG_COMPAT_32BIT_TIME
> and therefore don't provide the 32-bit system calls anymore.
>
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>

Thanks for working on this!

> -#if defined(__NR_ppoll)
> -	struct timespec t;
> +#if defined(__NR_ppoll_time64)
> +	struct __kernel_timespec t;
> 
>  	if (timeout >= 0) {
>  		t.tv_sec  = timeout / 1000;
>  		t.tv_nsec = (timeout % 1000) * 1000000;
>  	}
> -	return my_syscall5(__NR_ppoll, fds, nfds, (timeout >= 0) ? &t : NULL, 
> NULL, 0);
> +	return my_syscall5(__NR_ppoll_time64, fds, nfds, (timeout >= 0) ? &t 

This looks good to me.

> -#elif defined(__NR_ppoll_time64)
> -	struct __kernel_timespec t;
> : NULL, NULL, 0);
> +#elif defined(__NR_ppoll)
> +	struct timespec t;
> 
>  	if (timeout >= 0) {
>  		t.tv_sec  = timeout / 1000;
>  		t.tv_nsec = (timeout % 1000) * 1000000;
>  	}

This is not wrong, but for consistency, I would use
__kernel_old_timespec with the old syscall macros, rather
than the nolibc-defined type.

A different approach would be to rely on timespec/timeval/time_t
to always use the 64-bit types and then just pick the time64
macros on 32-bit vs the old macros on 64-bit builds.

> -	return my_syscall5(__NR_ppoll_time64, fds, nfds, (timeout >= 0) ? &t 
> : NULL, NULL, 0);
> +	return my_syscall5(__NR_ppoll, fds, nfds, (timeout >= 0) ? &t : NULL, 
> NULL, 0);
>  #else
>  	return my_syscall3(__NR_poll, fds, nfds, timeout);
>  #endif

I would think that we can remove the final #else clause here
and just use the __NR_ppoll case as #else. It would also make
sense to change the first #if to check for a 32-bit ABI.

> diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> index e91b7d947161..10c517a38f86 100644
> --- a/tools/include/nolibc/sys.h
> +++ b/tools/include/nolibc/sys.h
> @@ -772,22 +772,22 @@ int sys_select(int nfds, fd_set *rfds, fd_set 
> *wfds, fd_set *efds, struct timeva
>  	return my_syscall5(__NR__newselect, nfds, rfds, wfds, efds, timeout);
>  #elif defined(__NR_select)
>  	return my_syscall5(__NR_select, nfds, rfds, wfds, efds, timeout);
> -#elif defined(__NR_pselect6)
> -	struct timespec t;
> +#elif defined(__NR_pselect6_time64)
> +	struct __kernel_timespec t;

These probably need to be flipped around, so that
__NR_pselect6_time64/__NR_pselect6 comes first because the other
ones use the wrong type on 32-bit targets.

Probably also do the same thing here with the #ifdef checking
the architecture instead of the syscall macro.

       Arnd