From b31b286425b7f80f0f078dc00a567bb53be170f3 Mon Sep 17 00:00:00 2001
From: Olivier Goffart <olivier.goffart@slint.dev>
Date: Tue, 10 Nov 2026 08:26:37 +0000
Subject: [PATCH] aml: A store into a buffer keeps the buffer's length

Storing a buffer into a buffer replaced it, length included. As in
ACPICA, the source is now copied into the buffer, which keeps its length:
the rest is zeroed, or the source cut. An empty buffer takes the source's
length.

Found on a Dell XPS 13 7390, whose _BIF stores each text into a buffer one
byte longer, then sets that last byte for its null: it failed with
IndexOutOfBounds, and the battery read nothing.
---
 src/aml/object.rs |  9 +++++++--
 tests/store.asl   | 16 ++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/aml/object.rs b/src/aml/object.rs
index cc96af52..d1510b34 100644
--- a/src/aml/object.rs
+++ b/src/aml/object.rs
@@ -381,7 +381,7 @@ impl Object {
 
     /// Replace this object's contents with that of a `new` object, applying implicit casting rules
     /// as needed. This follows the NT interpreter's creative interpretation of implicit casts, which is
-    /// effectively a byte-wise transmutation.
+    /// effectively a byte-wise transmutation. A buffer keeps its length, unless it's empty.
     pub fn replace_with_implicit_casting(&mut self, new: Object) -> Result<(), AmlError> {
         let new_bytes = match new {
             Object::Integer(value) => &value.to_le_bytes(),
@@ -401,7 +401,12 @@ impl Object {
                 *value = String::from_utf8_lossy(new_bytes).split('\0').next().unwrap().to_string();
             }
             Object::Buffer(value) => {
-                *value = new_bytes.to_vec();
+                if value.is_empty() {
+                    value.resize(new_bytes.len(), 0);
+                }
+                let n = usize::min(new_bytes.len(), value.len());
+                value[..n].copy_from_slice(&new_bytes[..n]);
+                value[n..].fill(0);
             }
             _ => return Err(AmlError::InvalidImplicitCast { from: self.typ(), to: new.typ() }),
         }
diff --git a/tests/store.asl b/tests/store.asl
index 5feca531..f52c07da 100644
--- a/tests/store.asl
+++ b/tests/store.asl
@@ -177,6 +177,20 @@ DefinitionBlock ("", "DSDT", 2, "RSACPI", "TESTTABL", 0xF0F0F0F0)
         }
     }
 
+    Method (T10) {
+        Name(BUF, Buffer (4) { 0xff, 0xff, 0xff, 0xff })
+        BUF = Buffer () { 1, 2 }
+        CHEK(BUF, Buffer () { 1, 2, 0, 0 })
+        BUF = Buffer () { 1, 2, 3, 4, 5, 6 }
+        CHEK(BUF, Buffer () { 1, 2, 3, 4 })
+    }
+
+    Method (T11) {
+        Name(BUF, Buffer (0) {})
+        BUF = Buffer () { 1, 2 }
+        CHEK(BUF, Buffer () { 1, 2 })
+    }
+
     Method (MAIN, 0, NotSerialized) {
         T1()
         T2()
@@ -196,6 +210,8 @@ DefinitionBlock ("", "DSDT", 2, "RSACPI", "TESTTABL", 0xF0F0F0F0)
         U4() // references-8
         U5() // references-9
         U6() // references-10
+        T10()
+        T11()
 
         Return (FCNT)
     }