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

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Message-Id: <23019c9ad3a63d7026a60df8bc41934c3e74e564.1690733545.git.tanyuan@tinylab.org>
Date:   Mon, 31 Jul 2023 13:50:45 +0800
From:   Yuan Tan <tanyuan@...ylab.org>
To:     w@....eu, thomas@...ch.de
Cc:     falcon@...ylab.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, Yuan Tan <tanyuan@...ylab.org>
Subject: [PATCH v2 1/2] 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@...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);
+}
+
+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