std: xous: the basics of `os`

Add the basics to get the operating system running, including how to
exit the operating system.

Since Xous has no libc, there is no default entrypoint. Add a `_start`
entrypoint to the system-specific os module.

Signed-off-by: Sean Cross <sean@xobs.io>

2 files changed, 147 insertions, 1 deletions

diff --git a/library/std/src/sys/xous/mod.rs b/library/std/src/sys/xous/mod.rs
index 836647c81ba..92089e8384c 100644
--- a/library/std/src/sys/xous/mod.rs
+++ b/library/std/src/sys/xous/mod.rs
@@ -18,7 +18,6 @@ pub mod locks;
 pub mod net;
 #[path = "../unsupported/once.rs"]
 pub mod once;
-#[path = "../unsupported/os.rs"]
 pub mod os;
 #[path = "../unix/os_str.rs"]
 pub mod os_str;
diff --git a/library/std/src/sys/xous/os.rs b/library/std/src/sys/xous/os.rs
new file mode 100644
index 00000000000..3d19fa4b31a
--- /dev/null
+++ b/library/std/src/sys/xous/os.rs
@@ -0,0 +1,147 @@
+use super::unsupported;
+use crate::error::Error as StdError;
+use crate::ffi::{OsStr, OsString};
+use crate::fmt;
+use crate::io;
+use crate::marker::PhantomData;
+use crate::os::xous::ffi::Error as XousError;
+use crate::path::{self, PathBuf};
+
+#[cfg(not(test))]
+mod c_compat {
+    use crate::os::xous::ffi::exit;
+    extern "C" {
+        fn main() -> u32;
+    }
+
+    #[no_mangle]
+    pub extern "C" fn abort() {
+        exit(1);
+    }
+
+    #[no_mangle]
+    pub extern "C" fn _start() {
+        exit(unsafe { main() });
+    }
+
+    // This function is needed by the panic runtime. The symbol is named in
+    // pre-link args for the target specification, so keep that in sync.
+    #[no_mangle]
+    // NB. used by both libunwind and libpanic_abort
+    pub extern "C" fn __rust_abort() -> ! {
+        exit(101);
+    }
+}
+
+pub fn errno() -> i32 {
+    0
+}
+
+pub fn error_string(errno: i32) -> String {
+    Into::<XousError>::into(errno).to_string()
+}
+
+pub fn getcwd() -> io::Result<PathBuf> {
+    unsupported()
+}
+
+pub fn chdir(_: &path::Path) -> io::Result<()> {
+    unsupported()
+}
+
+pub struct SplitPaths<'a>(!, PhantomData<&'a ()>);
+
+pub fn split_paths(_unparsed: &OsStr) -> SplitPaths<'_> {
+    panic!("unsupported")
+}
+
+impl<'a> Iterator for SplitPaths<'a> {
+    type Item = PathBuf;
+    fn next(&mut self) -> Option<PathBuf> {
+        self.0
+    }
+}
+
+#[derive(Debug)]
+pub struct JoinPathsError;
+
+pub fn join_paths<I, T>(_paths: I) -> Result<OsString, JoinPathsError>
+where
+    I: Iterator<Item = T>,
+    T: AsRef<OsStr>,
+{
+    Err(JoinPathsError)
+}
+
+impl fmt::Display for JoinPathsError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        "not supported on this platform yet".fmt(f)
+    }
+}
+
+impl StdError for JoinPathsError {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "not supported on this platform yet"
+    }
+}
+
+pub fn current_exe() -> io::Result<PathBuf> {
+    unsupported()
+}
+
+pub struct Env(!);
+
+impl Env {
+    // FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
+    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
+        let Self(inner) = self;
+        match *inner {}
+    }
+}
+
+impl fmt::Debug for Env {
+    fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Self(inner) = self;
+        match *inner {}
+    }
+}
+
+impl Iterator for Env {
+    type Item = (OsString, OsString);
+    fn next(&mut self) -> Option<(OsString, OsString)> {
+        self.0
+    }
+}
+
+pub fn env() -> Env {
+    panic!("not supported on this platform")
+}
+
+pub fn getenv(_: &OsStr) -> Option<OsString> {
+    None
+}
+
+pub fn setenv(_: &OsStr, _: &OsStr) -> io::Result<()> {
+    Err(io::const_io_error!(io::ErrorKind::Unsupported, "cannot set env vars on this platform"))
+}
+
+pub fn unsetenv(_: &OsStr) -> io::Result<()> {
+    Err(io::const_io_error!(io::ErrorKind::Unsupported, "cannot unset env vars on this platform"))
+}
+
+pub fn temp_dir() -> PathBuf {
+    panic!("no filesystem on this platform")
+}
+
+pub fn home_dir() -> Option<PathBuf> {
+    None
+}
+
+pub fn exit(code: i32) -> ! {
+    crate::os::xous::ffi::exit(code as u32);
+}
+
+pub fn getpid() -> u32 {
+    panic!("no pids on this platform")
+}