Add MBR parser (#17)

Cargo.toml

@@ -3,10 +3,6 @@ name = "cuteloader"
 version = "0.1.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
-[dependencies]
-
 
 # panic behaviour
 

src/read_mbr.rs

@@ -0,0 +1,79 @@
+use x86_64::instructions::port::Port;
+
+#[derive(Debug)]
+struct PartitionEntry {
+    bootable: u8,
+    start_chs: [u8; 3],
+    partition_type: u8,
+    end_chs: [u8; 3],
+    start_lba: u32,
+    size_sectors: u32,
+}
+
+impl PartitionEntry {
+    fn new(buffer: &[u8]) -> Self {
+        Self {
+            bootable: buffer[0],
+            start_chs: [buffer[1], buffer[2], buffer[3]],
+            partition_type: buffer[4],
+            end_chs: [buffer[5], buffer[6], buffer[7]],
+            start_lba: u32::from_le_bytes([
+                buffer[8],
+                buffer[9],
+                buffer[10],
+                buffer[11],
+            ]),
+            size_sectors: u32::from_le_bytes([
+                buffer[12],
+                buffer[13],
+                buffer[14],
+                buffer[15],
+            ]),
+        }
+    }
+}
+
+fn read_disk_sector(buffer: &mut [u8], sector: u32) {
+    let ah = 0x02; // AH = 2 (Read sector)
+    let al = buffer.len() as u8;
+    let ch = (sector >> 8) as u8;
+    let cl = (sector & 0xFF) as u8;
+    let dh = 0; // DH = 0 (Head number)
+    let dl = 0x80; // DL = 0x80 (Drive number: 0x80 for first hard disk)
+
+    unsafe {
+        asm!(
+            "int 0x13",
+            in("ah") ah,
+            in("al") al,
+            in("ch") ch,
+            in("cl") cl,
+            in("dh") dh,
+            in("dl") dl,
+            inout("rcx") buffer.len() => _,
+            inout("rdi") buffer.as_mut_ptr() => _,
+        );
+    }
+}
+
+fn fetch_bootable_partitions(sector: u32) {
+    let mut mbr_buffer: [u8; 512] = [0; 512];
+    read_disk_sector(&mut mbr_buffer, sector);
+
+    let mut partition_entries: Vec<PartitionEntry> = Vec::new();
+    let mut bootable_parts: Vec<PartitionEntry> = Vec::new();
+    for i in 0..4 {
+        let offset = 446 + i * 16;
+        let entry_buffer = &mbr_buffer[offset..offset + 16];
+        let partition_entry = PartitionEntry::new(entry_buffer);
+        partition_entries.push(partition_entry);
+    }
+
+    for (i, entry) in partition_entries.iter().enumerate() {
+        if entry.bootable == 0x80 {
+		bootable_parts.push(entry)
+	}
+    }
+
+    bootable_parts
+}