Make read_exact function unsafe

Author: phil-opp

bios/stage-2/src/disk.rs

@@ -8,7 +8,7 @@ pub struct DiskAccess {
 }
 
 impl Read for DiskAccess {
-    fn read_exact(&mut self, len: usize) -> &[u8] {
+    unsafe fn read_exact(&mut self, len: usize) -> &[u8] {
         let current_sector_offset = usize::try_from(self.current_offset % 512).unwrap();
 
         static mut TMP_BUF: AlignedArrayBuffer<1024> = AlignedArrayBuffer {
@@ -70,7 +70,7 @@ impl Seek for DiskAccess {
 }
 
 pub trait Read {
-    fn read_exact(&mut self, len: usize) -> &[u8];
+    unsafe fn read_exact(&mut self, len: usize) -> &[u8];
     fn read_exact_into(&mut self, len: usize, buf: &mut dyn AlignedBuffer);
 }
 

bios/stage-2/src/fat.rs

@@ -34,7 +34,7 @@ struct Bpb {
 impl Bpb {
     fn parse<D: Read + Seek>(disk: &mut D) -> Self {
         disk.seek(SeekFrom::Start(0));
-        let raw = disk.read_exact(512);
+        let raw = unsafe { disk.read_exact(512) };
 
         let bytes_per_sector = u16::from_le_bytes(raw[11..13].try_into().unwrap());
         let sectors_per_cluster = raw[13];
@@ -483,21 +483,21 @@ where
         FatType::Fat32 => {
             let base = n as u64 * 4;
             disk.seek(SeekFrom::Start(fat_start + base));
-            let buf = disk.read_exact(4);
+            let buf = unsafe { disk.read_exact(4) };
             let buf: [u8; 4] = buf.try_into().unwrap();
             u32::from_le_bytes(buf) & 0x0FFFFFFF
         }
         FatType::Fat16 => {
             let base = n as u64 * 2;
             disk.seek(SeekFrom::Start(fat_start + base));
-            let buf = disk.read_exact(2);
+            let buf = unsafe { disk.read_exact(2) };
             let buf: [u8; 2] = buf.try_into().unwrap();
             u16::from_le_bytes(buf) as u32
         }
         FatType::Fat12 => {
             let base = n as u64 + (n as u64 / 2);
             disk.seek(SeekFrom::Start(fat_start + base));
-            let buf = disk.read_exact(2);
+            let buf = unsafe { disk.read_exact(2) };
             let buf: [u8; 2] = buf.try_into().unwrap();
             let entry16 = u16::from_le_bytes(buf);
             if n & 1 == 0 {