multiboot2: Get a mutable reference to the memory map

Author: YtvwlD

integration-test/bins/multiboot2_payload/src/main.rs

@@ -31,7 +31,7 @@ fn main(multiboot2_magic: u32, multiboot2_hdr: u32) -> anyhow::Result<()> {
     }
     log::debug!("multiboot2_hdr={multiboot2_hdr:x?}, multiboot2_magic=0x{multiboot2_magic:x?}");
 
-    let mbi_ptr = (multiboot2_hdr as *const u8).cast();
+    let mbi_ptr = (multiboot2_hdr as *mut u8).cast();
     let mbi = unsafe { BootInformation::load(mbi_ptr) }.map_err(anyhow::Error::msg)?;
     verify::run(&mbi)
 }

multiboot2/src/builder/information.rs

@@ -10,7 +10,7 @@ use crate::{
 use crate::builder::BoxedDst;
 use alloc::vec::Vec;
 use core::mem::size_of;
-use core::ops::Deref;
+use core::ops::{Deref, DerefMut};
 
 /// Holds the raw bytes of a boot information built with [`InformationBuilder`]
 /// on the heap. The bytes returned by [`BootInformationBytes::as_bytes`] are
@@ -33,6 +33,15 @@ impl BootInformationBytes {
         assert_eq!(slice.as_ptr().align_offset(8), 0);
         slice
     }
+
+    /// Returns the bytes mutably. They are guaranteed to be correctly aligned.
+    pub fn as_bytes_mut(&mut self) -> &mut [u8] {
+        let slice = &mut self.bytes[self.offset..self.offset + self.structure_len];
+        // At this point, the alignment is guaranteed. If not, something is
+        // broken fundamentally.
+        assert_eq!(slice.as_ptr().align_offset(8), 0);
+        slice
+    }
 }
 
 impl Deref for BootInformationBytes {
@@ -43,6 +52,12 @@ impl Deref for BootInformationBytes {
     }
 }
 
+impl DerefMut for BootInformationBytes {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.as_bytes_mut()
+    }
+}
+
 /// Builder to construct a valid Multiboot2 information dynamically at runtime.
 /// The tags will appear in the order of their corresponding enumeration,
 /// except for the END tag.
@@ -411,10 +426,10 @@ mod tests {
     #[cfg_attr(miri, ignore)]
     fn test_builder() {
         // Step 1/2: Build MBI
-        let mb2i_data = create_builder().build();
+        let mut mb2i_data = create_builder().build();
 
         // Step 2/2: Test the built MBI
-        let mb2i = unsafe { BootInformation::load(mb2i_data.as_ptr().cast()) }
+        let mb2i = unsafe { BootInformation::load(mb2i_data.as_mut_ptr().cast()) }
             .expect("generated information should be readable");
 
         assert_eq!(mb2i.basic_memory_info_tag().unwrap().memory_lower(), 640);