build flat x86 rust binary

boot1/src/main.rs

@@ -0,0 +1,57 @@
+#![no_std]
+#![no_main]
+
+use core::{arch::asm, panic::PanicInfo};
+
+const VGA_WIDTH: usize = 80;
+const VGA_HEIGHT: usize = 25;
+const VGA_SIZE: usize = VGA_WIDTH * VGA_HEIGHT;
+const VGA_ADDR: usize = 0xb8000;
+
+const STR: &[u8] = b"the quick brown fox jumps over the lazy dog";
+
+#[panic_handler]
+fn panic(_info: &PanicInfo) -> ! {
+  hlt()
+}
+
+// ```asm
+// 00000000  E800000000        call 0x5      ; call / pop gadget to load eip into ecx
+// 00000005  59                pop ecx
+// 00000006  81C15F000000      add ecx,0x5f
+// 0000000C  31C0              xor eax,eax
+// 0000000E  8D89D4FFFFFF      lea ecx,[ecx-0x2c]      ; length of string is 0x2b
+// 00000014  0FB611            movzx edx,byte [ecx]
+// 00000017  81CA001F0000      or edx,0x1f00
+// 0000001D  6689940000800B00  mov [eax+eax+0xb8000],dx
+// 00000025  40                inc eax
+// 00000026  41                inc ecx
+// 00000027  83F82B            cmp eax,byte +0x2b
+// 0000002A  75E8              jnz 0x14
+// 0000002C  66C70500800B0002  mov word [dword 0xb8000],0x1f02
+//          -1F
+// 00000035  F4                hlt
+// 00000036  EBFD              jmp short 0x35
+// ```
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+  let vga_buf: &'static mut [u16; VGA_SIZE] = unsafe { &mut *(VGA_ADDR as *mut [u16; VGA_SIZE]) };
+
+  for (i, b) in STR.iter().copied().enumerate() {
+    vga_buf[i] = 0x1f00 | u16::from(b);
+  }
+
+  vga_buf[0] = 0x1f02; //smiley
+
+  hlt()
+}
+
+#[inline]
+fn hlt() -> ! {
+  loop {
+    unsafe {
+      asm!("hlt");
+    }
+  }
+}
+