Rollup merge of #145973 - vexide:vex-std, r=tgross35

Add `std` support for `armv7a-vex-v5`

This PR adds standard library support for the VEX V5 Brain (`armv7a-vex-v5` target). It is more-or-less an updated version of the library-side work done in rust-lang/rust#131530.

This was a joint effort between me, `@lewisfm,` `@max-niederman,` `@Gavin-Niederman` and several other members of the [`vexide` project](https://github.com/vexide/).

## Background

VEXos is a fairly unconventional operating system, with user code running in a restricted enviornment with regards to I/O capabilities and whatnot. As such, several OS-dependent APIs are unsupported or have partial support (such as `std::net`, `std::process`, and most of `std::thread`). A more comprehensive list of what does or doesn't work is outlined in the [updated target documentation](https://github.com/vexide/rust/blob/vex-std/src/doc/rustc/src/platform-support/armv7a-vex-v5.md). Despite these limitations, we believe that `libstd` support on this target still has value to users, especially given the popular use of this hardware for educational purposes. For some previous discussion on this matter, see [this comment](https://github.com/rust-lang/rust/pull/131530#issuecomment-2432856841).

## SDK Linkage

VEXos doesn't really ship with an official `libc` or POSIX-style platform API (and though it does port newlib, these are stubbed on top of the underlying SDK). Instead, VEX provides their own SDK for calling platform APIs. Their official SDK is kept proprietary (with public headers), though open-source implementations exist. Following the precedent of the `armv6k-nintendo-3ds` team's work in rust-lang/rust#95897, we've opted not to directly link `libstd` to any SDK with the expectation that users will provide their own with one of the following options:
-  [`vex-sdk-download`](https://github.com/vexide/vex-sdk/tree/main/packages/vex-sdk-download), which downloads an official proprietary SDK from VEX using a build script.
- [`vex-sdk-jumptable`](https://crates.io/crates/vex-sdk-jumptable), which is a compatible, open-source reimplementation of the SDK using firmware jumps.
- [`vex-sdk-pros`](https://github.com/vexide/vex-sdk/tree/main/packages/vex-sdk-pros), which uses the [PROS kernel](https://github.com/purduesigbots/pros) as a provider for SDK functions.
- Linking their own implementation or stubbing the functions required by libstd.

 The `vex-sdk` crate used in the VEXos PAL provides `libc`-style FFI bindings for any compatible system library, so any of these options *should* work fine. A functional demo project using `vex-sdk-download` can be found [here](https://github.com/vexide/armv7a-vex-v5-demo/tree/main).

## Future Work

This PR implements virtually everything we are currently able to implement given the current capabilities of the platform. The exception to this is file directory enumeration, though the implementation of that is sufficiently [gross enough](https://github.com/vexide/vexide/blob/c6c5bad11e035cf4e51d429dca7e427210185ed4/packages/vexide-core/src/fs/mod.rs#L987) to drive us away from supporting this officially.

Additionally, I have a working branch implementing the `panic_unwind` runtime for this target, which is something that would be nice to see in the future, though given the volume of compiler changes i've deemed it out-of-scope for this PR.

17 files changed, 982 insertions, 1 deletions

diff --git a/library/std/Cargo.toml b/library/std/Cargo.toml
index 958cafb8f3d..888914a2f77 100644
--- a/library/std/Cargo.toml
+++ b/library/std/Cargo.toml
@@ -62,7 +62,7 @@ path = "../windows_targets"
 rand = { version = "0.9.0", default-features = false, features = ["alloc"] }
 rand_xorshift = "0.4.0"
 
-[target.'cfg(any(all(target_family = "wasm", target_os = "unknown"), target_os = "xous", all(target_vendor = "fortanix", target_env = "sgx")))'.dependencies]
+[target.'cfg(any(all(target_family = "wasm", target_os = "unknown"), target_os = "xous", target_os = "vexos", all(target_vendor = "fortanix", target_env = "sgx")))'.dependencies]
 dlmalloc = { version = "0.2.10", features = ['rustc-dep-of-std'] }
 
 [target.x86_64-fortanix-unknown-sgx.dependencies]
@@ -89,6 +89,11 @@ wasip2 = { version = '0.14.4', features = [
 r-efi = { version = "5.2.0", features = ['rustc-dep-of-std'] }
 r-efi-alloc = { version = "2.0.0", features = ['rustc-dep-of-std'] }
 
+[target.'cfg(target_os = "vexos")'.dependencies]
+vex-sdk = { version = "0.27.0", features = [
+    'rustc-dep-of-std',
+], default-features = false }
+
 [features]
 backtrace = [
     'addr2line/rustc-dep-of-std',
diff --git a/library/std/build.rs b/library/std/build.rs
index ef695601a44..8a5a785060c 100644
--- a/library/std/build.rs
+++ b/library/std/build.rs
@@ -52,6 +52,7 @@ fn main() {
         || target_os == "rtems"
         || target_os == "nuttx"
         || target_os == "cygwin"
+        || target_os == "vexos"
 
         // See src/bootstrap/src/core/build_steps/synthetic_targets.rs
         || env::var("RUSTC_BOOTSTRAP_SYNTHETIC_TARGET").is_ok()
diff --git a/library/std/src/env.rs b/library/std/src/env.rs
index e457cd61c75..6d716bd8544 100644
--- a/library/std/src/env.rs
+++ b/library/std/src/env.rs
@@ -1098,6 +1098,7 @@ pub mod consts {
     /// * `"redox"`
     /// * `"solaris"`
     /// * `"solid_asp3`
+    /// * `"vexos"`
     /// * `"vita"`
     /// * `"vxworks"`
     /// * `"xous"`
@@ -1148,6 +1149,7 @@ pub mod consts {
     ///
     /// <details><summary>Full list of possible values</summary>
     ///
+    /// * `"bin"`
     /// * `"exe"`
     /// * `"efi"`
     /// * `"js"`
diff --git a/library/std/src/sys/alloc/mod.rs b/library/std/src/sys/alloc/mod.rs
index 6d4b09494a3..2045b2fecc6 100644
--- a/library/std/src/sys/alloc/mod.rs
+++ b/library/std/src/sys/alloc/mod.rs
@@ -92,6 +92,9 @@ cfg_select! {
     target_os = "uefi" => {
         mod uefi;
     }
+    target_os = "vexos" => {
+        mod vexos;
+    }
     target_family = "wasm" => {
         mod wasm;
     }
diff --git a/library/std/src/sys/alloc/vexos.rs b/library/std/src/sys/alloc/vexos.rs
new file mode 100644
index 00000000000..c1fb6896a89
--- /dev/null
+++ b/library/std/src/sys/alloc/vexos.rs
@@ -0,0 +1,96 @@
+// FIXME(static_mut_refs): Do not allow `static_mut_refs` lint
+#![allow(static_mut_refs)]
+
+use crate::alloc::{GlobalAlloc, Layout, System};
+use crate::ptr;
+use crate::sync::atomic::{AtomicBool, Ordering};
+
+// Symbols for heap section boundaries defined in the target's linkerscript
+unsafe extern "C" {
+    static mut __heap_start: u8;
+    static mut __heap_end: u8;
+}
+
+static mut DLMALLOC: dlmalloc::Dlmalloc<Vexos> = dlmalloc::Dlmalloc::new_with_allocator(Vexos);
+
+struct Vexos;
+
+unsafe impl dlmalloc::Allocator for Vexos {
+    /// Allocs system resources
+    fn alloc(&self, _size: usize) -> (*mut u8, usize, u32) {
+        static INIT: AtomicBool = AtomicBool::new(false);
+
+        if !INIT.swap(true, Ordering::Relaxed) {
+            // This target has no growable heap, as user memory has a fixed
+            // size/location and VEXos does not manage allocation for us.
+            unsafe {
+                (
+                    (&raw mut __heap_start).cast::<u8>(),
+                    (&raw const __heap_end).offset_from_unsigned(&raw const __heap_start),
+                    0,
+                )
+            }
+        } else {
+            (ptr::null_mut(), 0, 0)
+        }
+    }
+
+    fn remap(&self, _ptr: *mut u8, _oldsize: usize, _newsize: usize, _can_move: bool) -> *mut u8 {
+        ptr::null_mut()
+    }
+
+    fn free_part(&self, _ptr: *mut u8, _oldsize: usize, _newsize: usize) -> bool {
+        false
+    }
+
+    fn free(&self, _ptr: *mut u8, _size: usize) -> bool {
+        return false;
+    }
+
+    fn can_release_part(&self, _flags: u32) -> bool {
+        false
+    }
+
+    fn allocates_zeros(&self) -> bool {
+        false
+    }
+
+    fn page_size(&self) -> usize {
+        0x1000
+    }
+}
+
+#[stable(feature = "alloc_system_type", since = "1.28.0")]
+unsafe impl GlobalAlloc for System {
+    #[inline]
+    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+        // SAFETY: DLMALLOC access is guaranteed to be safe because we are a single-threaded target, which
+        // guarantees unique and non-reentrant access to the allocator. As such, no allocator lock is used.
+        // Calling malloc() is safe because preconditions on this function match the trait method preconditions.
+        unsafe { DLMALLOC.malloc(layout.size(), layout.align()) }
+    }
+
+    #[inline]
+    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+        // SAFETY: DLMALLOC access is guaranteed to be safe because we are a single-threaded target, which
+        // guarantees unique and non-reentrant access to the allocator. As such, no allocator lock is used.
+        // Calling calloc() is safe because preconditions on this function match the trait method preconditions.
+        unsafe { DLMALLOC.calloc(layout.size(), layout.align()) }
+    }
+
+    #[inline]
+    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+        // SAFETY: DLMALLOC access is guaranteed to be safe because we are a single-threaded target, which
+        // guarantees unique and non-reentrant access to the allocator. As such, no allocator lock is used.
+        // Calling free() is safe because preconditions on this function match the trait method preconditions.
+        unsafe { DLMALLOC.free(ptr, layout.size(), layout.align()) }
+    }
+
+    #[inline]
+    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+        // SAFETY: DLMALLOC access is guaranteed to be safe because we are a single-threaded target, which
+        // guarantees unique and non-reentrant access to the allocator. As such, no allocator lock is used.
+        // Calling realloc() is safe because preconditions on this function match the trait method preconditions.
+        unsafe { DLMALLOC.realloc(ptr, layout.size(), layout.align(), new_size) }
+    }
+}
diff --git a/library/std/src/sys/env_consts.rs b/library/std/src/sys/env_consts.rs
index 711ba0a5f8a..573f540483b 100644
--- a/library/std/src/sys/env_consts.rs
+++ b/library/std/src/sys/env_consts.rs
@@ -323,6 +323,17 @@ pub mod os {
     pub const EXE_EXTENSION: &str = "efi";
 }
 
+#[cfg(target_os = "vexos")]
+pub mod os {
+    pub const FAMILY: &str = "";
+    pub const OS: &str = "vexos";
+    pub const DLL_PREFIX: &str = "";
+    pub const DLL_SUFFIX: &str = "";
+    pub const DLL_EXTENSION: &str = "";
+    pub const EXE_SUFFIX: &str = ".bin";
+    pub const EXE_EXTENSION: &str = "bin";
+}
+
 #[cfg(target_os = "visionos")]
 pub mod os {
     pub const FAMILY: &str = "unix";
diff --git a/library/std/src/sys/fs/mod.rs b/library/std/src/sys/fs/mod.rs
index 0276bf6e64c..64f5a6b36d3 100644
--- a/library/std/src/sys/fs/mod.rs
+++ b/library/std/src/sys/fs/mod.rs
@@ -35,6 +35,10 @@ cfg_select! {
         mod uefi;
         use uefi as imp;
     }
+    target_os = "vexos" => {
+        mod vexos;
+        use vexos as imp;
+    }
     target_os = "wasi" => {
         mod wasi;
         use wasi as imp;
diff --git a/library/std/src/sys/fs/vexos.rs b/library/std/src/sys/fs/vexos.rs
new file mode 100644
index 00000000000..f642e7cb074
--- /dev/null
+++ b/library/std/src/sys/fs/vexos.rs
@@ -0,0 +1,615 @@
+use crate::ffi::{OsString, c_char};
+use crate::fmt;
+use crate::fs::TryLockError;
+use crate::hash::Hash;
+use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, SeekFrom};
+use crate::path::{Path, PathBuf};
+use crate::sys::common::small_c_string::run_path_with_cstr;
+use crate::sys::time::SystemTime;
+use crate::sys::{unsupported, unsupported_err};
+
+#[expect(dead_code)]
+#[path = "unsupported.rs"]
+mod unsupported_fs;
+pub use unsupported_fs::{
+    DirBuilder, FileTimes, canonicalize, link, readlink, remove_dir_all, rename, rmdir, symlink,
+    unlink,
+};
+
+/// VEXos file descriptor.
+///
+/// This stores an opaque pointer to a [FatFs file object structure] managed by VEXos
+/// representing an open file on disk.
+///
+/// [FatFs file object structure]: https://github.com/Xilinx/embeddedsw/blob/master/lib/sw_services/xilffs/src/include/ff.h?rgh-link-date=2025-09-23T20%3A03%3A43Z#L215
+///
+/// # Safety
+///
+/// Since this platform uses a pointer to to an internal filesystem structure with a lifetime
+/// associated with it (rather than a UNIX-style file descriptor table), care must be taken to
+/// ensure that the pointer held by `FileDesc` is valid for as long as it exists.
+#[derive(Debug)]
+struct FileDesc(*mut vex_sdk::FIL);
+
+// SAFETY: VEXos's FDs can be used on a thread other than the one they were created on.
+unsafe impl Send for FileDesc {}
+// SAFETY: We assume an environment without threads (i.e. no RTOS).
+// (If there were threads, it is possible that a mutex would be required.)
+unsafe impl Sync for FileDesc {}
+
+pub struct File {
+    fd: FileDesc,
+}
+
+#[derive(Clone)]
+pub enum FileAttr {
+    Dir,
+    File { size: u64 },
+}
+
+pub struct ReadDir(!);
+
+pub struct DirEntry {
+    path: PathBuf,
+}
+
+#[derive(Clone, Debug)]
+pub struct OpenOptions {
+    read: bool,
+    write: bool,
+    append: bool,
+    truncate: bool,
+    create: bool,
+    create_new: bool,
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct FilePermissions {}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub struct FileType {
+    is_dir: bool,
+}
+
+impl FileAttr {
+    pub fn size(&self) -> u64 {
+        match self {
+            Self::File { size } => *size,
+            Self::Dir => 0,
+        }
+    }
+
+    pub fn perm(&self) -> FilePermissions {
+        FilePermissions {}
+    }
+
+    pub fn file_type(&self) -> FileType {
+        FileType { is_dir: matches!(self, FileAttr::Dir) }
+    }
+
+    pub fn modified(&self) -> io::Result<SystemTime> {
+        unsupported()
+    }
+
+    pub fn accessed(&self) -> io::Result<SystemTime> {
+        unsupported()
+    }
+
+    pub fn created(&self) -> io::Result<SystemTime> {
+        unsupported()
+    }
+}
+
+impl FilePermissions {
+    pub fn readonly(&self) -> bool {
+        false
+    }
+
+    pub fn set_readonly(&mut self, _readonly: bool) {
+        panic!("Perimissions do not exist")
+    }
+}
+
+impl FileType {
+    pub fn is_dir(&self) -> bool {
+        self.is_dir
+    }
+
+    pub fn is_file(&self) -> bool {
+        !self.is_dir
+    }
+
+    pub fn is_symlink(&self) -> bool {
+        // No symlinks in VEXos - entries are either files or directories.
+        false
+    }
+}
+
+impl fmt::Debug for ReadDir {
+    fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0
+    }
+}
+
+impl Iterator for ReadDir {
+    type Item = io::Result<DirEntry>;
+
+    fn next(&mut self) -> Option<io::Result<DirEntry>> {
+        self.0
+    }
+}
+
+impl DirEntry {
+    pub fn path(&self) -> PathBuf {
+        self.path.clone()
+    }
+
+    pub fn file_name(&self) -> OsString {
+        self.path.file_name().unwrap_or_default().into()
+    }
+
+    pub fn metadata(&self) -> io::Result<FileAttr> {
+        stat(&self.path)
+    }
+
+    pub fn file_type(&self) -> io::Result<FileType> {
+        Ok(self.metadata()?.file_type())
+    }
+}
+
+impl OpenOptions {
+    pub fn new() -> OpenOptions {
+        OpenOptions {
+            read: false,
+            write: false,
+            append: false,
+            truncate: false,
+            create: false,
+            create_new: false,
+        }
+    }
+
+    pub fn read(&mut self, read: bool) {
+        self.read = read;
+    }
+    pub fn write(&mut self, write: bool) {
+        self.write = write;
+    }
+    pub fn append(&mut self, append: bool) {
+        self.append = append;
+    }
+    pub fn truncate(&mut self, truncate: bool) {
+        self.truncate = truncate;
+    }
+    pub fn create(&mut self, create: bool) {
+        self.create = create;
+    }
+    pub fn create_new(&mut self, create_new: bool) {
+        self.create_new = create_new;
+    }
+}
+
+impl File {
+    pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
+        run_path_with_cstr(path, &|path| {
+            // Enforce the invariants of `create_new`/`create`.
+            //
+            // Since VEXos doesn't have anything akin to POSIX's `oflags`, we need to enforce
+            // the requirements that `create_new` can't have an existing file and `!create`
+            // doesn't create a file ourselves.
+            if !opts.read && (opts.write || opts.append) && (opts.create_new || !opts.create) {
+                let status = unsafe { vex_sdk::vexFileStatus(path.as_ptr()) };
+
+                if opts.create_new && status != 0 {
+                    return Err(io::const_error!(io::ErrorKind::AlreadyExists, "file exists",));
+                } else if !opts.create && status == 0 {
+                    return Err(io::const_error!(
+                        io::ErrorKind::NotFound,
+                        "no such file or directory",
+                    ));
+                }
+            }
+
+            let file = match opts {
+                // read + write - unsupported
+                OpenOptions { read: true, write: true, .. } => {
+                    return Err(io::const_error!(
+                        io::ErrorKind::InvalidInput,
+                        "opening files with read and write access is unsupported on this target",
+                    ));
+                }
+
+                // read
+                OpenOptions {
+                    read: true,
+                    write: false,
+                    append: _,
+                    truncate: false,
+                    create: false,
+                    create_new: false,
+                } => unsafe { vex_sdk::vexFileOpen(path.as_ptr(), c"".as_ptr()) },
+
+                // append
+                OpenOptions {
+                    read: false,
+                    write: _,
+                    append: true,
+                    truncate: false,
+                    create: _,
+                    create_new: _,
+                } => unsafe { vex_sdk::vexFileOpenWrite(path.as_ptr()) },
+
+                // write
+                OpenOptions {
+                    read: false,
+                    write: true,
+                    append: false,
+                    truncate,
+                    create: _,
+                    create_new: _,
+                } => unsafe {
+                    if *truncate {
+                        vex_sdk::vexFileOpenCreate(path.as_ptr())
+                    } else {
+                        // Open in append, but jump to the start of the file.
+                        let fd = vex_sdk::vexFileOpenWrite(path.as_ptr());
+                        vex_sdk::vexFileSeek(fd, 0, 0);
+                        fd
+                    }
+                },
+
+                _ => {
+                    return Err(io::const_error!(io::ErrorKind::InvalidInput, "invalid argument"));
+                }
+            };
+
+            if file.is_null() {
+                Err(io::const_error!(io::ErrorKind::NotFound, "could not open file"))
+            } else {
+                Ok(Self { fd: FileDesc(file) })
+            }
+        })
+    }
+
+    pub fn file_attr(&self) -> io::Result<FileAttr> {
+        // `vexFileSize` returns -1 upon error, so u64::try_from will fail on error.
+        if let Ok(size) = u64::try_from(unsafe {
+            // SAFETY: `self.fd` contains a valid pointer to `FIL` for this struct's lifetime.
+            vex_sdk::vexFileSize(self.fd.0)
+        }) {
+            Ok(FileAttr::File { size })
+        } else {
+            Err(io::const_error!(io::ErrorKind::InvalidData, "failed to get file size"))
+        }
+    }
+
+    pub fn fsync(&self) -> io::Result<()> {
+        self.flush()
+    }
+
+    pub fn datasync(&self) -> io::Result<()> {
+        self.flush()
+    }
+
+    pub fn lock(&self) -> io::Result<()> {
+        unsupported()
+    }
+
+    pub fn lock_shared(&self) -> io::Result<()> {
+        unsupported()
+    }
+
+    pub fn try_lock(&self) -> Result<(), TryLockError> {
+        Err(TryLockError::Error(unsupported_err()))
+    }
+
+    pub fn try_lock_shared(&self) -> Result<(), TryLockError> {
+        Err(TryLockError::Error(unsupported_err()))
+    }
+
+    pub fn unlock(&self) -> io::Result<()> {
+        unsupported()
+    }
+
+    pub fn truncate(&self, _size: u64) -> io::Result<()> {
+        unsupported()
+    }
+
+    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        let len = buf.len() as u32;
+        let buf_ptr = buf.as_mut_ptr();
+        let read = unsafe {
+            // SAFETY: `self.fd` contains a valid pointer to `FIL` for this struct's lifetime.
+            vex_sdk::vexFileRead(buf_ptr.cast::<c_char>(), 1, len, self.fd.0)
+        };
+
+        if read < 0 {
+            Err(io::const_error!(io::ErrorKind::Other, "could not read from file"))
+        } else {
+            Ok(read as usize)
+        }
+    }
+
+    pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
+        crate::io::default_read_vectored(|b| self.read(b), bufs)
+    }
+
+    #[inline]
+    pub fn is_read_vectored(&self) -> bool {
+        false
+    }
+
+    pub fn read_buf(&self, cursor: BorrowedCursor<'_>) -> io::Result<()> {
+        crate::io::default_read_buf(|b| self.read(b), cursor)
+    }
+
+    pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
+        let len = buf.len() as u32;
+        let buf_ptr = buf.as_ptr();
+        let written = unsafe {
+            // SAFETY: `self.fd` contains a valid pointer to `FIL` for this struct's lifetime.
+            vex_sdk::vexFileWrite(buf_ptr.cast_mut().cast::<c_char>(), 1, len, self.fd.0)
+        };
+
+        if written < 0 {
+            Err(io::const_error!(io::ErrorKind::Other, "could not write to file"))
+        } else {
+            Ok(written as usize)
+        }
+    }
+
+    pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
+        crate::io::default_write_vectored(|b| self.write(b), bufs)
+    }
+
+    #[inline]
+    pub fn is_write_vectored(&self) -> bool {
+        false
+    }
+
+    pub fn flush(&self) -> io::Result<()> {
+        unsafe {
+            // SAFETY: `self.fd` contains a valid pointer to `FIL` for this struct's lifetime.
+            vex_sdk::vexFileSync(self.fd.0);
+        }
+        Ok(())
+    }
+
+    pub fn tell(&self) -> io::Result<u64> {
+        // SAFETY: `self.fd` contains a valid pointer to `FIL` for this struct's lifetime.
+        let position = unsafe { vex_sdk::vexFileTell(self.fd.0) };
+
+        position.try_into().map_err(|_| {
+            io::const_error!(io::ErrorKind::InvalidData, "failed to get current location in file")
+        })
+    }
+
+    pub fn size(&self) -> Option<io::Result<u64>> {
+        None
+    }
+
+    pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
+        const SEEK_SET: i32 = 0;
+        const SEEK_CUR: i32 = 1;
+        const SEEK_END: i32 = 2;
+
+        fn try_convert_offset<T: TryInto<u32>>(offset: T) -> io::Result<u32> {
+            offset.try_into().map_err(|_| {
+                io::const_error!(
+                    io::ErrorKind::InvalidInput,
+                    "cannot seek to an offset too large to fit in a 32 bit integer",
+                )
+            })
+        }
+
+        // SAFETY: `self.fd` contains a valid pointer to `FIL` for this struct's lifetime.
+        match pos {
+            SeekFrom::Start(offset) => unsafe {
+                map_fresult(vex_sdk::vexFileSeek(self.fd.0, try_convert_offset(offset)?, SEEK_SET))?
+            },
+            SeekFrom::End(offset) => unsafe {
+                if offset >= 0 {
+                    map_fresult(vex_sdk::vexFileSeek(
+                        self.fd.0,
+                        try_convert_offset(offset)?,
+                        SEEK_END,
+                    ))?
+                } else {
+                    // `vexFileSeek` does not support seeking with negative offset, meaning
+                    // we have to calculate the offset from the end of the file ourselves.
+
+                    // Seek to the end of the file to get the end position in the open buffer.
+                    map_fresult(vex_sdk::vexFileSeek(self.fd.0, 0, SEEK_END))?;
+                    let end_position = self.tell()?;
+
+                    map_fresult(vex_sdk::vexFileSeek(
+                        self.fd.0,
+                        // NOTE: Files internally use a 32-bit representation for stream
+                        // position, so `end_position as i64` should never overflow.
+                        try_convert_offset(end_position as i64 + offset)?,
+                        SEEK_SET,
+                    ))?
+                }
+            },
+            SeekFrom::Current(offset) => unsafe {
+                if offset >= 0 {
+                    map_fresult(vex_sdk::vexFileSeek(
+                        self.fd.0,
+                        try_convert_offset(offset)?,
+                        SEEK_CUR,
+                    ))?
+                } else {
+                    // `vexFileSeek` does not support seeking with negative offset, meaning
+                    // we have to calculate the offset from the stream position ourselves.
+                    map_fresult(vex_sdk::vexFileSeek(
+                        self.fd.0,
+                        try_convert_offset((self.tell()? as i64) + offset)?,
+                        SEEK_SET,
+                    ))?
+                }
+            },
+        }
+
+        Ok(self.tell()?)
+    }
+
+    pub fn duplicate(&self) -> io::Result<File> {
+        unsupported()
+    }
+
+    pub fn set_permissions(&self, _perm: FilePermissions) -> io::Result<()> {
+        unsupported()
+    }
+
+    pub fn set_times(&self, _times: FileTimes) -> io::Result<()> {
+        unsupported()
+    }
+}
+
+impl fmt::Debug for File {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("File").field("fd", &self.fd.0).finish()
+    }
+}
+impl Drop for File {
+    fn drop(&mut self) {
+        unsafe { vex_sdk::vexFileClose(self.fd.0) };
+    }
+}
+
+pub fn readdir(_p: &Path) -> io::Result<ReadDir> {
+    // While there *is* a userspace function for reading file directories,
+    // the necessary implementation cannot currently be done cleanly, as
+    // VEXos does not expose directory length to user programs.
+    //
+    // This means that we would need to create a large fixed-length buffer
+    // and hope that the folder's contents didn't exceed that buffer's length,
+    // which obviously isn't behavior we want to rely on in the standard library.
+    unsupported()
+}
+
+pub fn set_perm(_p: &Path, _perm: FilePermissions) -> io::Result<()> {
+    unsupported()
+}
+
+pub fn exists(path: &Path) -> io::Result<bool> {
+    run_path_with_cstr(path, &|path| Ok(unsafe { vex_sdk::vexFileStatus(path.as_ptr()) } != 0))
+}
+
+pub fn stat(p: &Path) -> io::Result<FileAttr> {
+    // `vexFileStatus` returns 3 if the given path is a directory, 1 if the path is a
+    // file, or 0 if no such path exists.
+    const FILE_STATUS_DIR: u32 = 3;
+
+    run_path_with_cstr(p, &|c_path| {
+        let file_type = unsafe { vex_sdk::vexFileStatus(c_path.as_ptr()) };
+
+        // We can't get the size if its a directory because we cant open it as a file
+        if file_type == FILE_STATUS_DIR {
+            Ok(FileAttr::Dir)
+        } else {
+            let mut opts = OpenOptions::new();
+            opts.read(true);
+            let file = File::open(p, &opts)?;
+            file.file_attr()
+        }
+    })
+}
+
+pub fn lstat(p: &Path) -> io::Result<FileAttr> {
+    // Symlinks aren't supported in this filesystem
+    stat(p)
+}
+
+// Cannot use `copy` from `common` here, since `File::set_permissions` is unsupported on this target.
+pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
+    use crate::fs::File;
+
+    // NOTE: If `from` is a directory, this call should fail due to vexFileOpen* returning null.
+    let mut reader = File::open(from)?;
+    let mut writer = File::create(to)?;
+
+    io::copy(&mut reader, &mut writer)
+}
+
+fn map_fresult(fresult: vex_sdk::FRESULT) -> io::Result<()> {
+    // VEX uses a derivative of FatFs (Xilinx's xilffs library) for filesystem operations.
+    match fresult {
+        vex_sdk::FRESULT::FR_OK => Ok(()),
+        vex_sdk::FRESULT::FR_DISK_ERR => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "internal function reported an unrecoverable hard error",
+        )),
+        vex_sdk::FRESULT::FR_INT_ERR => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "internal error in filesystem runtime",
+        )),
+        vex_sdk::FRESULT::FR_NOT_READY => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "the storage device could not be prepared to work",
+        )),
+        vex_sdk::FRESULT::FR_NO_FILE => Err(io::const_error!(
+            io::ErrorKind::NotFound,
+            "could not find the file in the directory"
+        )),
+        vex_sdk::FRESULT::FR_NO_PATH => Err(io::const_error!(
+            io::ErrorKind::NotFound,
+            "a directory in the path name could not be found",
+        )),
+        vex_sdk::FRESULT::FR_INVALID_NAME => Err(io::const_error!(
+            io::ErrorKind::InvalidInput,
+            "the given string is invalid as a path name",
+        )),
+        vex_sdk::FRESULT::FR_DENIED => Err(io::const_error!(
+            io::ErrorKind::PermissionDenied,
+            "the required access for this operation was denied",
+        )),
+        vex_sdk::FRESULT::FR_EXIST => Err(io::const_error!(
+            io::ErrorKind::AlreadyExists,
+            "an object with the same name already exists in the directory",
+        )),
+        vex_sdk::FRESULT::FR_INVALID_OBJECT => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "invalid or null file/directory object",
+        )),
+        vex_sdk::FRESULT::FR_WRITE_PROTECTED => Err(io::const_error!(
+            io::ErrorKind::PermissionDenied,
+            "a write operation was performed on write-protected media",
+        )),
+        vex_sdk::FRESULT::FR_INVALID_DRIVE => Err(io::const_error!(
+            io::ErrorKind::InvalidInput,
+            "an invalid drive number was specified in the path name",
+        )),
+        vex_sdk::FRESULT::FR_NOT_ENABLED => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "work area for the logical drive has not been registered",
+        )),
+        vex_sdk::FRESULT::FR_NO_FILESYSTEM => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "valid FAT volume could not be found on the drive",
+        )),
+        vex_sdk::FRESULT::FR_MKFS_ABORTED => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "failed to create filesystem volume"
+        )),
+        vex_sdk::FRESULT::FR_TIMEOUT => Err(io::const_error!(
+            io::ErrorKind::TimedOut,
+            "the function was canceled due to a timeout of thread-safe control",
+        )),
+        vex_sdk::FRESULT::FR_LOCKED => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "the operation to the object was rejected by file sharing control",
+        )),
+        vex_sdk::FRESULT::FR_NOT_ENOUGH_CORE => {
+            Err(io::const_error!(io::ErrorKind::OutOfMemory, "not enough memory for the operation"))
+        }
+        vex_sdk::FRESULT::FR_TOO_MANY_OPEN_FILES => Err(io::const_error!(
+            io::ErrorKind::Uncategorized,
+            "maximum number of open files has been reached",
+        )),
+        vex_sdk::FRESULT::FR_INVALID_PARAMETER => {
+            Err(io::const_error!(io::ErrorKind::InvalidInput, "a given parameter was invalid"))
+        }
+        _ => unreachable!(), // C-style enum
+    }
+}
diff --git a/library/std/src/sys/pal/mod.rs b/library/std/src/sys/pal/mod.rs
index 513121c6d30..dd5e83ee570 100644
--- a/library/std/src/sys/pal/mod.rs
+++ b/library/std/src/sys/pal/mod.rs
@@ -45,6 +45,10 @@ cfg_select! {
         mod trusty;
         pub use self::trusty::*;
     }
+    target_os = "vexos" => {
+        mod vexos;
+        pub use self::vexos::*;
+    }
     all(target_os = "wasi", target_env = "p2") => {
         mod wasip2;
         pub use self::wasip2::*;
diff --git a/library/std/src/sys/pal/vexos/mod.rs b/library/std/src/sys/pal/vexos/mod.rs
new file mode 100644
index 00000000000..61a34b0f68a
--- /dev/null
+++ b/library/std/src/sys/pal/vexos/mod.rs
@@ -0,0 +1,80 @@
+#[path = "../unsupported/os.rs"]
+pub mod os;
+#[path = "../unsupported/pipe.rs"]
+pub mod pipe;
+pub mod time;
+
+#[expect(dead_code)]
+#[path = "../unsupported/common.rs"]
+mod unsupported_common;
+
+pub use unsupported_common::{
+    decode_error_kind, init, is_interrupted, unsupported, unsupported_err,
+};
+
+use crate::arch::global_asm;
+use crate::ptr;
+use crate::sys::stdio;
+use crate::time::{Duration, Instant};
+
+global_asm!(
+    r#"
+    .section .boot, "ax"
+    .global _boot
+
+    _boot:
+        ldr sp, =__stack_top @ Set up the user stack.
+        b _start             @ Jump to the Rust entrypoint.
+    "#
+);
+
+#[cfg(not(test))]
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn _start() -> ! {
+    unsafe extern "C" {
+        static mut __bss_start: u8;
+        static mut __bss_end: u8;
+
+        fn main() -> i32;
+    }
+
+    // Clear the .bss (uninitialized statics) section by filling it with zeroes.
+    // This is required, since the compiler assumes it will be zeroed on first access.
+    ptr::write_bytes(
+        &raw mut __bss_start,
+        0,
+        (&raw mut __bss_end).offset_from_unsigned(&raw mut __bss_start),
+    );
+
+    main();
+
+    cleanup();
+    abort_internal()
+}
+
+// SAFETY: must be called only once during runtime cleanup.
+// NOTE: this is not guaranteed to run, for example when the program aborts.
+pub unsafe fn cleanup() {
+    let exit_time = Instant::now();
+    const FLUSH_TIMEOUT: Duration = Duration::from_millis(15);
+
+    // Force the serial buffer to flush
+    while exit_time.elapsed() < FLUSH_TIMEOUT {
+        vex_sdk::vexTasksRun();
+
+        // If the buffer has been fully flushed, exit the loop
+        if vex_sdk::vexSerialWriteFree(stdio::STDIO_CHANNEL) == (stdio::STDOUT_BUF_SIZE as i32) {
+            break;
+        }
+    }
+}
+
+pub fn abort_internal() -> ! {
+    unsafe {
+        vex_sdk::vexSystemExitRequest();
+
+        loop {
+            vex_sdk::vexTasksRun();
+        }
+    }
+}
diff --git a/library/std/src/sys/pal/vexos/time.rs b/library/std/src/sys/pal/vexos/time.rs
new file mode 100644
index 00000000000..f95d96cd27a
--- /dev/null
+++ b/library/std/src/sys/pal/vexos/time.rs
@@ -0,0 +1,28 @@
+use crate::time::Duration;
+
+#[expect(dead_code)]
+#[path = "../unsupported/time.rs"]
+mod unsupported_time;
+pub use unsupported_time::{SystemTime, UNIX_EPOCH};
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
+pub struct Instant(Duration);
+
+impl Instant {
+    pub fn now() -> Instant {
+        let micros = unsafe { vex_sdk::vexSystemHighResTimeGet() };
+        Self(Duration::from_micros(micros))
+    }
+
+    pub fn checked_sub_instant(&self, other: &Instant) -> Option<Duration> {
+        self.0.checked_sub(other.0)
+    }
+
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant(self.0.checked_add(*other)?))
+    }
+
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant(self.0.checked_sub(*other)?))
+    }
+}
diff --git a/library/std/src/sys/random/mod.rs b/library/std/src/sys/random/mod.rs
index 1e0eec07b50..3c5a4c82a9f 100644
--- a/library/std/src/sys/random/mod.rs
+++ b/library/std/src/sys/random/mod.rs
@@ -101,6 +101,7 @@ cfg_select! {
     any(
         all(target_family = "wasm", target_os = "unknown"),
         target_os = "xous",
+        target_os = "vexos",
     ) => {
         // FIXME: finally remove std support for wasm32-unknown-unknown
         // FIXME: add random data generation to xous
@@ -116,6 +117,7 @@ cfg_select! {
     all(target_family = "wasm", target_os = "unknown"),
     all(target_os = "wasi", target_env = "p2"),
     target_os = "xous",
+    target_os = "vexos",
 )))]
 pub fn hashmap_random_keys() -> (u64, u64) {
     let mut buf = [0; 16];
diff --git a/library/std/src/sys/stdio/mod.rs b/library/std/src/sys/stdio/mod.rs
index 7436e4d9de4..404ac877926 100644
--- a/library/std/src/sys/stdio/mod.rs
+++ b/library/std/src/sys/stdio/mod.rs
@@ -29,6 +29,10 @@ cfg_select! {
         mod uefi;
         pub use uefi::*;
     }
+    target_os = "vexos" => {
+        mod vexos;
+        pub use vexos::*;
+    }
     all(target_os = "wasi", target_env = "p1") => {
         mod wasip1;
         pub use wasip1::*;
diff --git a/library/std/src/sys/stdio/vexos.rs b/library/std/src/sys/stdio/vexos.rs
new file mode 100644
index 00000000000..1f2251c6421
--- /dev/null
+++ b/library/std/src/sys/stdio/vexos.rs
@@ -0,0 +1,100 @@
+use crate::io;
+
+pub struct Stdin;
+pub struct Stdout;
+pub type Stderr = Stdout;
+
+pub const STDIO_CHANNEL: u32 = 1;
+
+impl Stdin {
+    pub const fn new() -> Stdin {
+        Stdin
+    }
+}
+
+impl io::Read for Stdin {
+    fn read(&mut self, mut buf: &mut [u8]) -> io::Result<usize> {
+        let mut count = 0;
+
+        for out_byte in buf.iter_mut() {
+            let byte = unsafe { vex_sdk::vexSerialReadChar(STDIO_CHANNEL) };
+            if byte < 0 {
+                break;
+            }
+
+            *out_byte = byte as u8;
+            count += 1;
+        }
+
+        Ok(count)
+    }
+}
+
+impl Stdout {
+    pub const fn new() -> Stdout {
+        Stdout
+    }
+}
+
+impl io::Write for Stdout {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let mut written = 0;
+
+        // HACK: VEXos holds an internal ringbuffer for serial writes that is flushed to USB1
+        // roughly every millisecond by `vexTasksRun`. For writes larger than 2048 bytes, we
+        // must block until that buffer is flushed to USB1 before writing the rest of `buf`.
+        //
+        // This is fairly nonstandard for a `write` implementation, but it avoids a guaranteed
+        // recursive panic when using macros such as `print!` to write large amounts of data
+        // (buf.len() > 2048) to stdout at once.
+        for chunk in buf.chunks(STDOUT_BUF_SIZE) {
+            if unsafe { vex_sdk::vexSerialWriteFree(STDIO_CHANNEL) as usize } < chunk.len() {
+                self.flush().unwrap();
+            }
+
+            let count: usize = unsafe {
+                vex_sdk::vexSerialWriteBuffer(STDIO_CHANNEL, chunk.as_ptr(), chunk.len() as u32)
+            }
+            .try_into()
+            .map_err(|_| {
+                io::const_error!(io::ErrorKind::Uncategorized, "internal write error occurred")
+            })?;
+
+            written += count;
+
+            // This is a sanity check to ensure that we don't end up with non-contiguous
+            // buffer writes. e.g. a chunk gets only partially written, but we continue
+            // attempting to write the remaining chunks.
+            //
+            // In practice, this should never really occur since the previous flush ensures
+            // enough space in FIFO to write the entire chunk to vexSerialWriteBuffer.
+            if count != chunk.len() {
+                break;
+            }
+        }
+
+        Ok(written)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        // This may block for up to a millisecond.
+        unsafe {
+            while (vex_sdk::vexSerialWriteFree(STDIO_CHANNEL) as usize) != STDOUT_BUF_SIZE {
+                vex_sdk::vexTasksRun();
+            }
+        }
+
+        Ok(())
+    }
+}
+
+pub const STDIN_BUF_SIZE: usize = 4096;
+pub const STDOUT_BUF_SIZE: usize = 2048;
+
+pub fn is_ebadf(_err: &io::Error) -> bool {
+    false
+}
+
+pub fn panic_output() -> Option<impl io::Write> {
+    Some(Stdout::new())
+}
diff --git a/library/std/src/sys/thread/mod.rs b/library/std/src/sys/thread/mod.rs
index 6bb7fc1a20e..3bd83dd760a 100644
--- a/library/std/src/sys/thread/mod.rs
+++ b/library/std/src/sys/thread/mod.rs
@@ -81,6 +81,13 @@ cfg_select! {
         ))]
         pub use unsupported::set_name;
     }
+    target_os = "vexos" => {
+        mod vexos;
+        pub use vexos::{sleep, yield_now};
+        #[expect(dead_code)]
+        mod unsupported;
+        pub use unsupported::{Thread, available_parallelism, current_os_id, set_name, DEFAULT_MIN_STACK_SIZE};
+    }
     all(target_os = "wasi", target_env = "p1") => {
         mod wasip1;
         pub use wasip1::{DEFAULT_MIN_STACK_SIZE, sleep, yield_now};
diff --git a/library/std/src/sys/thread/vexos.rs b/library/std/src/sys/thread/vexos.rs
new file mode 100644
index 00000000000..d917dde4d0b
--- /dev/null
+++ b/library/std/src/sys/thread/vexos.rs
@@ -0,0 +1,17 @@
+use crate::time::{Duration, Instant};
+
+pub fn yield_now() {
+    unsafe {
+        vex_sdk::vexTasksRun();
+    }
+}
+
+pub fn sleep(dur: Duration) {
+    let start = Instant::now();
+
+    while start.elapsed() < dur {
+        unsafe {
+            vex_sdk::vexTasksRun();
+        }
+    }
+}
diff --git a/library/std/src/sys/thread_local/mod.rs b/library/std/src/sys/thread_local/mod.rs
index cff74857c47..d5c795093cf 100644
--- a/library/std/src/sys/thread_local/mod.rs
+++ b/library/std/src/sys/thread_local/mod.rs
@@ -29,6 +29,7 @@ cfg_select! {
         target_os = "uefi",
         target_os = "zkvm",
         target_os = "trusty",
+        target_os = "vexos",
     ) => {
         mod no_threads;
         pub use no_threads::{EagerStorage, LazyStorage, thread_local_inner};
@@ -98,6 +99,7 @@ pub(crate) mod guard {
             target_os = "uefi",
             target_os = "zkvm",
             target_os = "trusty",
+            target_os = "vexos",
         ) => {
             pub(crate) fn enable() {
                 // FIXME: Right now there is no concept of "thread exit" on