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 <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Yuan Tan <[email protected]>
---
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
On 2023-07-31 13:50:45+0800, Yuan Tan wrote:
> [..]
> +static __attribute__((unused))
> +int pipe(int pipefd[2])
> +{
> + pipe2(pipefd, 0);
This is missing a "return".
> +}
> +
> +
> /*
> * int prctl(int option, unsigned long arg2, unsigned long arg3,
> * unsigned long arg4, unsigned long arg5);
> --
> 2.34.1
>
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 <[email protected]>
> Link: https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Yuan Tan <[email protected]>
> ---
> 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
>