Add rustix::process::exit to terminate processes

src/backend/libc/process/syscalls.rs

@@ -742,3 +742,12 @@ pub(crate) fn getgroups(buf: &mut [Gid]) -> io::Result<usize> {
 
     unsafe { ret_usize(c::getgroups(len, buf.as_mut_ptr().cast()) as isize) }
 }
+
+#[cfg(not(target_os = "wasi"))]
+#[inline]
+pub(crate) fn _exit(status: i32) -> ! {
+    unsafe {
+        libc::_exit(status);
+    }
+    unreachable!("_exit failed to exit the process");
+}

src/backend/linux_raw/process/syscalls.rs

@@ -620,3 +620,10 @@ pub(crate) fn getgroups(buf: &mut [Gid]) -> io::Result<usize> {
         ))
     }
 }
+
+#[inline]
+pub(crate) fn _exit(status: i32) -> ! {
+    unsafe {
+        syscall_noreturn!(__NR_exit_group, c_int(status));
+    };
+}

src/process/exit.rs

@@ -1,8 +1,6 @@
 use crate::backend;
 
-/// `EXIT_SUCCESS` for use with [`exit`].
-///
-/// [`exit`]: std::process::exit
+/// `EXIT_SUCCESS` for use with [`exit`] or [`std::process::exit`].
 ///
 /// # References
 ///  - [POSIX]
@@ -12,9 +10,7 @@ use crate::backend;
 /// [Linux]: https://man7.org/linux/man-pages/man3/exit.3.html
 pub const EXIT_SUCCESS: i32 = backend::c::EXIT_SUCCESS;
 
-/// `EXIT_FAILURE` for use with [`exit`].
-///
-/// [`exit`]: std::process::exit
+/// `EXIT_FAILURE` for use with [`exit`] or [`std::process::exit`].
 ///
 /// # References
 ///  - [POSIX]
@@ -34,3 +30,18 @@ pub const EXIT_FAILURE: i32 = backend::c::EXIT_FAILURE;
 /// [`Signal::Abort`]: crate::process::Signal::Abort
 #[cfg(not(any(target_os = "espidf", target_os = "wasi")))]
 pub const EXIT_SIGNALED_SIGABRT: i32 = backend::c::EXIT_SIGNALED_SIGABRT;
+
+/// Immediately exits the process. Exiting via this function does not unwind the
+/// stack and does not call any further user code. This behavior is similar to
+/// the POSIX/C `_Exit` and `_exit` functions.
+///
+/// # References
+///  - [POSIX]
+///  - [Linux]
+///
+/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdlib.h.html
+/// [Linux]: https://www.man7.org/linux/man-pages/man2/exit.2.html
+#[inline]
+pub fn exit(status: i32) -> ! {
+    backend::process::syscalls::_exit(status);
+}