linux-kernel - Re: [PATCH 1/2] tools/nolibc: Provide vfork()

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Message-ID: <2ece41af-9500-447c-8203-5c57024e39f9@t-8ch.de>
Date: Mon, 9 Jun 2025 17:25:31 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Mark Brown <broonie@...nel.org>
Cc: Willy Tarreau <w@....eu>, Christian Brauner <brauner@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Shuah Khan <shuah@...nel.org>, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 1/2] tools/nolibc: Provide vfork()

Hi Mark,

On 2025-06-09 16:08:56+0100, Mark Brown wrote:
> To allow testing of vfork() support in the arm64 basic-gcs test provide an
> implementation for nolibc, using the vfork() syscall if one is available
> and otherwise clone3(). We implement in terms of clone3() since the order
> of the arguments for clone() varies between architectures.

Thanks for the patch!

Do you want to take this series through your tree?

> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  tools/include/nolibc/sys.h | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> index 9556c69a6ae1..e056da010f64 100644
> --- a/tools/include/nolibc/sys.h
> +++ b/tools/include/nolibc/sys.h
> @@ -22,6 +22,7 @@
>  #include <linux/time.h>
>  #include <linux/auxvec.h>
>  #include <linux/fcntl.h> /* for O_* and AT_* */
> +#include <linux/sched.h> /* for clone_args */
>  #include <linux/stat.h>  /* for statx() */
>  
>  #include "errno.h"
> @@ -340,6 +341,34 @@ pid_t fork(void)
>  	return __sysret(sys_fork());
>  }
>  
> +#ifndef sys_vfork
> +static __attribute__((unused))
> +pid_t sys_vfork(void)
> +{
> +#ifdef __NR_vfork
> +	return my_syscall0(__NR_vfork);
> +#elif defined(__NR_clone3)
> +	/*
> +	 * clone() could be used but has different argument orders per
> +	 * architecture.
> +	 */
> +	struct clone_args args = {
> +		.flags		= CLONE_VM | CLONE_VFORK,
> +		.exit_signal	= SIGCHLD,
> +	};
> +
> +	return my_syscall2(__NR_clone3, &args, sizeof(args));
> +#else
> +	return __nolibc_enosys(__func__);
> +#endif
> +}
> +#endif
> +
> +static __attribute__((unused))
> +pid_t vfork(void)
> +{
> +	return __sysret(sys_vfork());
> +}

Could you also add a test to nolibc-test.c?
Maybe extend test_fork() with a flag to use either fork() or vfork().
And maybe change the exit() in the test to _exit(); not that it would
make a difference for nolibc (yet).

>  
>  /*
>   * int fsync(int fd);
> 
> -- 
> 2.39.5
>