From 3ea68a7f8bd6184d853e043efe46d329b15da699 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Ma=C4=87kowski?= <mmac@google.com>
Date: Wed, 15 Jul 2026 13:33:29 +0000
Subject: [PATCH] feat(overlay): support resolving local fixups

---
 src/model/overlay.rs | 94 +++++++++++++++++++++++++++++++++++++++++++-
 tests/overlay.rs     | 13 ++++++
 2 files changed, 106 insertions(+), 1 deletion(-)

diff --git a/src/model/overlay.rs b/src/model/overlay.rs
index dfdd81e..4b6c57e 100644
--- a/src/model/overlay.rs
+++ b/src/model/overlay.rs
@@ -17,7 +17,9 @@ use alloc::vec::Vec;
 use crate::error::OverlayError;
 use crate::fdt::Fdt;
 use crate::model::{DeviceTree, DeviceTreeNode};
-use crate::overlay::{Fragment, FragmentTarget, NODE_SYMBOLS, Overlay, PHANDLE_PROPS, get_phandle};
+use crate::overlay::{
+    Fragment, FragmentTarget, NODE_LOCAL_FIXUPS, NODE_SYMBOLS, Overlay, PHANDLE_PROPS, get_phandle,
+};
 use crate::{Node, Property};
 
 /// A utility struct for applying device tree overlays efficiently.
@@ -92,6 +94,8 @@ impl<'a> OverlayApplier<'a> {
     /// Returns an error when applying the overlay fails because of a malformed
     /// overlay data.
     pub fn apply_overlay_tree(&mut self, mut overlay: DeviceTree) -> Result<(), OverlayError> {
+        relocate_local_phandles(&mut overlay, self.max_phandle)?;
+
         let overlay_view = Overlay {
             node: &overlay.root,
         };
@@ -224,6 +228,26 @@ fn update_phandles_recursive(
     }
 }
 
+/// Relocates all local phandles defined in `overlay` and updates internal
+/// references specified by `/__local_fixups__` by adding `phandle_offset`.
+fn relocate_local_phandles(
+    overlay: &mut DeviceTree,
+    phandle_offset: u32,
+) -> Result<(), OverlayError> {
+    if phandle_offset == 0 {
+        overlay.root.remove_child(NODE_LOCAL_FIXUPS);
+        return Ok(());
+    }
+
+    offset_node_phandles(&mut overlay.root, phandle_offset)?;
+
+    if let Some(fixup_node) = overlay.root.remove_child(NODE_LOCAL_FIXUPS) {
+        update_local_references(&mut overlay.root, &fixup_node, phandle_offset)?;
+    }
+
+    Ok(())
+}
+
 /// Relocates all local phandles defined in `overlay` and updates internal
 /// references specified by `/__local_fixups__` by adding `phandle_offset`.
 #[allow(unused)]
@@ -245,6 +269,74 @@ fn offset_node_phandles(node: &mut DeviceTreeNode, offset: u32) -> Result<(), Ov
     Ok(())
 }
 
+const OFFSET_LEN: usize = size_of::<u32>();
+
+fn update_local_references(
+    target_node: &mut DeviceTreeNode,
+    fixup_node: &DeviceTreeNode,
+    offset: u32,
+) -> Result<(), OverlayError> {
+    for fixup_prop in fixup_node.properties() {
+        let prop_name = fixup_prop.name();
+        let target_prop =
+            target_node
+                .property_mut(prop_name)
+                .ok_or_else(|| OverlayError::InvalidLocalFixup {
+                    prop: prop_name.to_string(),
+                    offset: 0,
+                })?;
+
+        let fixup_val = fixup_prop.value();
+        if fixup_val.len() % OFFSET_LEN != 0 {
+            return Err(OverlayError::InvalidLocalFixup {
+                prop: prop_name.to_string(),
+                offset: 0,
+            });
+        }
+
+        let mut new_value = (&*target_prop).value().to_owned();
+        for chunk in fixup_val.as_chunks::<OFFSET_LEN>().0 {
+            let ref_offset = u32::from_be_bytes(*chunk) as usize;
+            let end_offset = ref_offset.checked_add(OFFSET_LEN).ok_or_else(|| {
+                OverlayError::InvalidLocalFixup {
+                    prop: prop_name.to_string(),
+                    offset: ref_offset,
+                }
+            })?;
+            if end_offset > new_value.len() {
+                return Err(OverlayError::InvalidLocalFixup {
+                    prop: prop_name.to_string(),
+                    offset: ref_offset,
+                });
+            }
+            let phandle_bytes = &new_value[ref_offset..end_offset];
+            let old_phandle = u32::from_be_bytes(phandle_bytes.try_into().map_err(|_| {
+                OverlayError::MalformedData("overlay inner slice length mismatch".to_string())
+            })?);
+            let new_phandle = old_phandle
+                .checked_add(offset)
+                .filter(|&v| v != u32::MAX)
+                .ok_or(OverlayError::PhandleOverflow)?;
+            new_value[ref_offset..ref_offset + 4].copy_from_slice(&new_phandle.to_be_bytes());
+        }
+        target_prop.set_value(new_value);
+    }
+
+    for fixup_child in fixup_node.children() {
+        let child_name = fixup_child.name();
+        let target_child =
+            target_node
+                .child_mut(child_name)
+                .ok_or_else(|| OverlayError::InvalidLocalFixup {
+                    prop: child_name.to_string(),
+                    offset: 0,
+                })?;
+        update_local_references(target_child, fixup_child, offset)?;
+    }
+
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use alloc::vec;
diff --git a/tests/overlay.rs b/tests/overlay.rs
index ddf89d3..a20a6d2 100644
--- a/tests/overlay.rs
+++ b/tests/overlay.rs
@@ -47,6 +47,19 @@ fn apply_overlay_target_path() {
     assert_eq!(fdt_soc.property("status").unwrap().as_str(), Ok("okay"));
 }
 
+#[test]
+fn apply_overlay_with_local_fixups() {
+    let mut base = apply_overlay!(
+        "overlay_local_fixups_base.dtb",
+        "overlay_local_fixups_overlay.dtb"
+    );
+
+    // Base had max phandle 1, so overlay phandle 1 should be relocated to 2.
+    let dev = base.find_node_mut("/dev@200").unwrap();
+    assert_eq!(dev.property("phandle").unwrap().as_u32().unwrap(), 2);
+    assert_eq!(dev.property("clocks").unwrap().value(), &[0, 0, 0, 2]);
+}
+
 #[test]
 fn apply_overlay_dependent_fragments() {
     // Just verify it applies without error