Parse FDT header

Cargo.toml

@@ -17,6 +17,7 @@ alloc = []
 std = ["alloc"]
 
 [dependencies]
+zerocopy = { version = "0.8", features = ["derive"] }
 
 [lints.rust]
 deprecated-safe = "warn"

clippy.toml

@@ -0,0 +1 @@
+allow-unwrap-in-tests = true

src/error.rs

@@ -0,0 +1,72 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Error types for the `dtoolkit` crate.
+
+use core::fmt;
+
+/// An error that can occur when parsing a device tree.
+#[derive(Debug)]
+#[non_exhaustive]
+pub struct FdtError {
+    offset: usize,
+    /// The type of the error that has occurred.
+    pub kind: FdtErrorKind,
+}
+
+impl FdtError {
+    pub(crate) fn new(kind: FdtErrorKind, offset: usize) -> Self {
+        Self { offset, kind }
+    }
+}
+
+/// The kind of an error that can occur when parsing a device tree.
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum FdtErrorKind {
+    /// The magic number of the device tree is invalid.
+    InvalidMagic,
+    /// The Device Tree version is not supported by this library.
+    UnsupportedVersion(u32),
+    /// The length of the device tree is invalid.
+    InvalidLength,
+    /// The header failed validation.
+    InvalidHeader(&'static str),
+    /// An invalid token was encountered.
+    BadToken(u32),
+    /// A read from data at invalid offset was attempted.
+    InvalidOffset,
+    /// An invalid string was encountered.
+    InvalidString,
+}
+
+impl fmt::Display for FdtError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} at offset {}", self.kind, self.offset)
+    }
+}
+
+impl fmt::Display for FdtErrorKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            FdtErrorKind::InvalidMagic => write!(f, "invalid FDT magic number"),
+            FdtErrorKind::UnsupportedVersion(version) => {
+                write!(f, "the FDT version {version} is not supported")
+            }
+            FdtErrorKind::InvalidLength => write!(f, "invalid FDT length"),
+            FdtErrorKind::InvalidHeader(msg) => {
+                write!(f, "FDT header has failed validation: {msg}")
+            }
+            FdtErrorKind::BadToken(token) => write!(f, "bad FDT token: 0x{token:x}"),
+            FdtErrorKind::InvalidOffset => write!(f, "invalid offset in FDT"),
+            FdtErrorKind::InvalidString => write!(f, "invalid string in FDT"),
+        }
+    }
+}
+
+impl core::error::Error for FdtError {}