[PATCH v3 1/2] tools/nolibc: add pipe() and pipe2() support

From: Yuan Tan
Date: Tue Aug 01 2023 - 11:40:25 EST

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

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@xxxxxxxxxxx>
Link: https://lore.kernel.org/all/20230729100401.GA4577@xxxxxx/
Signed-off-by: Yuan Tan <tanyuan@xxxxxxxxxxx>
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..56f63eb48a1b 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_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);