linux-kernel - Re: [PATCH v2 1/2] tools/nolibc: add pipe() and pipe2() support

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Message-ID: <f5bcb0b3-7165-4e06-a5a5-9535d5ce3c4e@t-8ch.de>
Date:   Mon, 31 Jul 2023 08:07:44 +0200
From:   Thomas Weißschuh <thomas@...ch.de>
To:     Yuan Tan <tanyuan@...ylab.org>
Cc:     w@....eu, falcon@...ylab.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 1/2] tools/nolibc: add pipe() and pipe2() support

On 2023-07-31 13:50:45+0800, Yuan Tan wrote:
> According to manual page [1], posix spec [2] and source code like
> arch/mips/kernel/syscall.c, for historic reasons, the sys_pipe() syscall
> on some architectures has an unusual calling convention.  It returns
> results in two registers which means there is no need for it to do
> verify the validity of a userspace pointer argument.  Historically that
> used to be expensive in Linux.  These days the performance advantage is
> negligible.
> 
> Nolibc doesn't support the unusual calling convention above, luckily
> Linux provides a generic sys_pipe2() with an additional flags argument
> from 2.6.27. If flags is 0, then pipe2() is the same as pipe(). So here
> we use sys_pipe2() to implement the pipe().
> 
> pipe2() is also provided to allow users to use flags argument on demand.
> 
> [1]: https://man7.org/linux/man-pages/man2/pipe.2.html
> [2]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/pipe.html
> 
> Suggested-by: Zhangjin Wu <falcon@...ylab.org>
> Link: https://lore.kernel.org/all/20230729100401.GA4577@1wt.eu/
> Signed-off-by: Yuan Tan <tanyuan@...ylab.org>
> ---
>  tools/include/nolibc/sys.h | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> index 8bfe7db20b80..9fec09c22dbe 100644
> --- a/tools/include/nolibc/sys.h
> +++ b/tools/include/nolibc/sys.h
> @@ -752,6 +752,30 @@ int open(const char *path, int flags, ...)
>  }
>  
>  
> +/*
> + * int pipe2(int pipefd[2], int flags);
> + * int pipe(int pipefd[2]);
> + */
> +
> +static __attribute__((unused))
> +int sys_pipe2(int pipefd[2], int flags)
> +{
> +	return my_syscall2(__NR_pipe, pipefd, flags);
> +}

Should be __NR_pipe2.

> +static __attribute__((unused))
> +int pipe2(int pipefd[2], int flags)
> +{
> +	return __sysret(sys_pipe2(pipefd, flags));
> +}
> +
> +static __attribute__((unused))
> +int pipe(int pipefd[2])
> +{
> +	pipe2(pipefd, 0);
> +}
> +
> +
>  /*
>   * int prctl(int option, unsigned long arg2, unsigned long arg3,
>   *                       unsigned long arg4, unsigned long arg5);
> -- 
> 2.34.1
>