Hermit: use sys_read_entropy syscall

src/hermit.rs

@@ -0,0 +1,21 @@
+use crate::Error;
+use core::{cmp::min, mem::MaybeUninit, num::NonZeroU32};
+
+extern "C" {
+ fn sys_read_entropy(buffer: *mut u8, length: usize, flags: u32) -> isize;
+}
+
+pub fn getrandom_inner(mut dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
+ while !dest.is_empty() {
+ let res = unsafe { sys_read_entropy(dest.as_mut_ptr() as *mut u8, dest.len(), 0) };
+ if res < 0 {
+ // SAFETY: all Hermit error codes use i32 under the hood:
+ // https://github.com/hermitcore/libhermit-rs/blob/master/src/errno.rs
+ let code = unsafe { NonZeroU32::new_unchecked((-res) as u32) };
+ return Err(code.into());
+ }
+ let len = min(res as usize, dest.len());
+ dest = &mut dest[len..];
+ }
+ Ok(())
+}

src/lib.rs

@@ -24,7 +24,7 @@
 //! | Fuchsia OS | `*‑fuchsia` | [`cprng_draw`]
 //! | Redox | `*‑redox` | `/dev/urandom`
 //! | Haiku | `*‑haiku` | `/dev/urandom` (identical to `/dev/random`)
-//! | Hermit | `x86_64-*-hermit` | [`RDRAND`]
+//! | Hermit | `*-hermit` | [`sys_read_entropy`]
 //! | SGX | `x86_64‑*‑sgx` | [`RDRAND`]
 //! | VxWorks | `*‑wrs‑vxworks‑*` | `randABytes` after checking entropy pool initialization with `randSecure`
 //! | ESP-IDF | `*‑espidf` | [`esp_fill_random`]
@@ -179,6 +179,7 @@
 //! [`module`]: https://rustwasm.github.io/wasm-bindgen/reference/attributes/on-js-imports/module.html
 //! [CommonJS modules]: https://nodejs.org/api/modules.html
 //! [ES modules]: https://nodejs.org/api/esm.html
+//! [`sys_read_entropy`]: https://hermitcore.github.io/libhermit-rs/hermit/fn.sys_read_entropy.html
 
 #![doc(
  html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
@@ -245,8 +246,8 @@ cfg_if! {
  #[path = "openbsd.rs"] mod imp;
  } else if #[cfg(all(target_arch = "wasm32", target_os = "wasi"))] {
  #[path = "wasi.rs"] mod imp;
- } else if #[cfg(all(target_arch = "x86_64", target_os = "hermit"))] {
- #[path = "rdrand.rs"] mod imp;
+ } else if #[cfg(target_os = "hermit")] {
+ #[path = "hermit.rs"] mod imp;
  } else if #[cfg(target_os = "vxworks")] {
  mod util_libc;
  #[path = "vxworks.rs"] mod imp;