1 files changed, 29 insertions, 0 deletions
diff --git a/src/hermit.rs b/src/hermit.rs
new file mode 100644
index 0000000..c4f6194
--- /dev/null
+++ b/src/hermit.rs
@@ -0,0 +1,29 @@
+//! Implementation for Hermit
+use crate::Error;
+use core::{mem::MaybeUninit, num::NonZeroU32};
+
+/// Minimum return value which we should get from syscalls in practice,
+/// because Hermit uses positive `i32`s for error codes:
+/// https://github.com/hermitcore/libhermit-rs/blob/main/src/errno.rs
+const MIN_RET_CODE: isize = -(i32::MAX as isize);
+
+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) };
+        // Positive `isize`s can be safely casted to `usize`
+        if res > 0 && (res as usize) <= dest.len() {
+            dest = &mut dest[res as usize..];
+        } else {
+            let err = match res {
+                MIN_RET_CODE..=-1 => NonZeroU32::new(-res as u32).unwrap().into(),
+                _ => Error::UNEXPECTED,
+            };
+            return Err(err);
+        }
+    }
+    Ok(())
+}