Add an execve function to runtime.

`execveat` isn't always supported, so add `execve` too, to allow
`execveat` to be emulated.

src/imp/linux_raw/syscalls.rs

@@ -95,8 +95,8 @@ use linux_raw_sys::general::{__NR_mmap2, __NR_set_thread_area};
 use linux_raw_sys::general::{__NR_ppoll, sigset_t};
 use linux_raw_sys::v5_11::general::__NR_mremap;
 use linux_raw_sys::v5_4::general::{
-    __NR_clone, __NR_eventfd2, __NR_execveat, __NR_getrandom, __NR_membarrier, __NR_mlock2,
-    __NR_preadv2, __NR_prlimit64, __NR_pwritev2, __NR_userfaultfd,
+    __NR_clone, __NR_eventfd2, __NR_execve, __NR_execveat, __NR_getrandom, __NR_membarrier,
+    __NR_mlock2, __NR_preadv2, __NR_prlimit64, __NR_pwritev2, __NR_userfaultfd,
 };
 #[cfg(target_pointer_width = "64")]
 use {super::conv::loff_t_from_u64, linux_raw_sys::general::__NR_mmap};
@@ -1600,6 +1600,19 @@ pub(crate) unsafe fn execveat(
     ))
 }
 
+pub(crate) unsafe fn execve(
+    path: &ZStr,
+    args: *const *const u8,
+    env_vars: *const *const u8,
+) -> io::Error {
+    ret_error(syscall3_readonly(
+        nr(__NR_execve),
+        c_str(path),
+        void_star(args as _),
+        void_star(env_vars as _),
+    ))
+}
+
 #[inline]
 pub(crate) fn wait(waitopts: WaitOptions) -> io::Result<Option<(Pid, WaitStatus)>> {
     _waitpid(!0, waitopts)

src/runtime.rs

@@ -220,13 +220,13 @@ pub unsafe fn fork() -> io::Result<Option<Pid>> {
     imp::syscalls::fork()
 }
 
-/// `execveat(path.as_z_str(), args, env_vars)`—Execute a new command using
-/// the current process.
+/// `execveat(dirfd, path.as_z_str(), argv, envp, flags)`—Execute a new
+/// command using the current process.
 ///
 /// # Safety
 ///
-/// The `args` and `env_vars` slices must be NUL-terminated, and their contents
-/// must be pointers to NUL-terminated byte arrays.
+/// The `argv` and `envp` pointers must point to NUL-terminated arrays, and
+/// their contents must be pointers to NUL-terminated byte arrays.
 ///
 /// # References
 ///  - [Linux]
@@ -244,3 +244,21 @@ pub unsafe fn execveat<Fd: AsFd>(
     let dirfd = dirfd.as_fd();
     imp::syscalls::execveat(dirfd, path, argv, envp, flags)
 }
+
+/// `execve(path.as_z_str(), argv, envp)`—Execute a new command using the
+/// current process.
+///
+/// # Safety
+///
+/// The `argv` and `envp` pointers must point to NUL-terminated arrays, and
+/// their contents must be pointers to NUL-terminated byte arrays.
+///
+/// # References
+///  - [Linux]
+///
+/// [Linux]: https://man7.org/linux/man-pages/man2/execve.2.html
+#[inline]
+#[cfg(linux_raw)]
+pub unsafe fn execve(path: &ZStr, argv: *const *const u8, envp: *const *const u8) -> io::Error {
+    imp::syscalls::execve(path, argv, envp)
+}