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@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); -- 2.34.1
