Commit 3ec38af6 authored Aug 01, 2023 by Yuan Tan Committed by Willy Tarreau Aug 23, 2023

tools/nolibc: add pipe() and pipe2() support

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@tinylab.org>
Link: https://lore.kernel.org/all/20230729100401.GA4577@1wt.eu/


Signed-off-by: Yuan Tan <tanyuan@tinylab.org>
Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>

parent e7d0129d

tools/include/nolibc/sys.h

+24 −0

Original line number	Diff line number	Diff line
		@@ -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_pipe2, pipefd, flags);
		}

		static __attribute__((unused))
		int pipe2(int pipefd[2], int flags)
		{
		return __sysret(sys_pipe2(pipefd, flags));
		}

		static __attribute__((unused))
		int pipe(int pipefd[2])
		{
		return pipe2(pipefd, 0);
		}


		/*
		* int prctl(int option, unsigned long arg2, unsigned long arg3,
		* unsigned long arg4, unsigned long arg5);