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.
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
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