fixed addr gdt, serial

docs/mem_layout.md

@@ -17,7 +17,21 @@
 | Reserved | 0x0c8000 - 0x0f0000 | bios expansions                                 |
 | Reserved | 0x0f0000 - 0x100000 | motherboard bios                                |
 
+### Allocations
+
+- 0x00500 - 0x04000: stage 1/2 stack
+- 0x04000 - 0x06a00: globals
+- 0x07c00 - 0x07e00: stage 1 text
+- 0x07e00 - 0x08000: gpt partition header
+- 0x08000 - 0x08200: stage 2 partition table entry
+- 0x08200 - 0x0c000: stage 2 text, stage 3 stack
+- 0x0c000          : gdt
+- 0x10000          : stage 3 text
+
 0x10000: stage 3
 
-TODO: once we're in real mode, repurpose s2 and s3 for a stack
+TODO: once we're in real mode, repurpose s2 for a stack
-TODO: load s4 into a separate memory region
+TODO: load s3 into a separate memory region
+
+TODO: use some fixed known memory address for the GDT, rather than putting it in stage 2.
+      That way, we can safely overwrite stage 2 once we're done with it.

include/layout.s

@@ -9,6 +9,7 @@
 %define S2_DATA        S2_LOAD_ADDR
 %define S2_ENTRYPOINT  (S2_DATA_ADDR + S2_DATA_LEN)
 
+%define GDT_ADDR       0xc000
 %define S3_LOAD_ADDR   0x10000
 
 ; %define MEMMAP          0x6a00

justfile

@@ -9,29 +9,33 @@ run:
     -m 512M \
     -drive format=raw,file=disk.bin
 
-#-bios seabios/out/bios.bin
+run_serial:
+  qemu-system-x86_64 \
+    -serial stdio \
+    -no-reboot \
+    -m 512M \
+    -drive format=raw,file=disk.bin
+
+run_reset:
+  qemu-system-x86_64 \
+    -monitor stdio \
+    -no-reboot \
+    -m 512M \
+    -drive if=pflash,file=reset.bin,format=raw
 
-build: build_stage_1 build_stage_2
+build_reset:
+  nasm -f bin -werror -o reset.bin reset.s
 
-build_stage_1:
+#-bios seabios/out/bios.bin
-  nasm -f bin {{common_flags}} -o stage_1/stage_1.bin stage_1/main.s
 
-build_stage_2:
+build:
-  nasm -f elf {{common_flags}} -o stage_2/prelude.o stage_2/prelude.s
+  cargo xtask build
-  nasm -f elf {{common_flags}} -o stage_2/main.o stage_2/main.s
-  nasm -f elf {{common_flags}} -o stage_2/a20.o stage_2/a20.s
-  {{ld32}} -m elf_i386 -T stage_2/link.ld -o stage_2/stage_2.bin stage_2/*.o
 
 mkimg:
   dd if=/dev/zero of=disk.bin bs=440 count=1 conv=notrunc
   dd if=build/stage_1/s1.bin of=disk.bin conv=notrunc
   dd if=build/s23.bin of=disk.bin bs=512 seek=70 conv=notrunc
 
-# build:
-#   nasm -f bin -Iinclude -o boot0.bin boot0.s
-#   cd boot1; cargo build --release
-#   # nasm -f bin -Iinclude -o boot1.bin boot1.s
-
 zero_disk:
   dd if=/dev/zero of=disk.bin bs=512 count=1000
 

reset.s

@@ -0,0 +1,14 @@
+; flash seems to get mapped to ff000
+; reset vector is f000:fff0 = ffff0
+; so there's ff0 = 4080 bytes of something before the reset vector. what is it?
+
+[bits 16]
+[org 0xff000]
+
+times (0xff0 - ($ - $$)) db 0x00
+
+  mov eax, 0xcafeface
+  hlt
+
+times (0x1000 - ($ - $$)) db 0xf4
+

stage_2/main.s

@@ -36,6 +36,12 @@ s2_main:
   mov cx, 0x3f00
   int 0x10
 
+  ; Copy the GDT
+  mov cx, GDT_FLAT_LEN
+  mov si, gdt_flat
+  mov di, GDT_ADDR
+  rep movsb
+
   ; Ensure interrupts are definitely disabled.
   cli
 
@@ -124,7 +130,6 @@ global gdt_flat_slice
 ; - 7: present (must be set)
 ;
 
-; FIXME: copy this to a fixed memory location
 align 8
 gdt_flat:
   ; First GDT entry must be 0.
@@ -161,8 +166,6 @@ gdt_flat:
      11001111b,  \
      0x00
 
-global gdt_flat
-
 GDT_FLAT_LEN equ ($ - gdt_flat)
 
 GDT_FLAT_IDX_CODE_32 equ (gdt_flat.segment_code_32 - gdt_flat)

stage_3/src/com.rs

@@ -0,0 +1,92 @@
+use core::{fmt, hint};
+
+use crate::ioport;
+
+pub struct Com {
+    port: u16,
+}
+
+pub struct ComError;
+
+impl Com {
+    pub unsafe fn init(port: u16) -> Result<Self, ComError> {
+        const ECHO_BYTE: u8 = 0x5a;
+        
+        let echo = unsafe {
+            // Unset DLAB
+            ioport::outb(port + 3, 0x00);
+            // Disable interrupts
+            ioport::outb(port + 1, 0x00);
+            // Set DLAB
+            ioport::outb(port + 3, 0x80);
+            // Set baud rate divisor to 00 01 (115200)
+            ioport::outb(port + 0, 0x01);
+            ioport::outb(port + 1, 0x00);
+            // 8 bits, no parity, one stop bit
+            ioport::outb(port + 3, 0x03);
+            // Enable FIFO, clear them, with 14-byte threshold
+            ioport::outb(port + 2, 0xc7);
+            // IRQs enabled, RTS/DSR set
+            ioport::outb(port + 4, 0x0b);
+            // Set loopback mode
+            ioport::outb(port + 4, 0x1e);
+            ioport::outb(port + 0, ECHO_BYTE);
+
+            ioport::inb(port + 0)
+        };
+
+        if echo != ECHO_BYTE {
+            return Err(ComError);
+        }
+
+        unsafe {
+            ioport::outb(port + 4, 0x0f);
+        }
+
+        Ok(Self {
+            port,
+        })
+    }
+
+    pub fn poll_has_data(&self) -> bool {
+        unsafe { ioport::inb(self.port + 5) & 0x01 != 0 }
+    }
+
+    pub fn read_poll(&mut self) -> u8 {
+        while !self.poll_has_data() {
+            hint::spin_loop();
+        }
+        unsafe { ioport::inb(self.port) }
+    }
+
+    pub fn poll_has_space(&self) -> bool {
+        unsafe { ioport::inb(self.port + 5) & 0x20 != 0 }
+    }
+
+    pub fn write_poll(&mut self, x: u8) {
+        while !self.poll_has_space() {
+            hint::spin_loop();
+        }
+        unsafe {
+            ioport::outb(self.port, x);
+        }
+    }
+}
+
+impl fmt::Write for Com {
+  fn write_str(&mut self, s: &str) -> fmt::Result {
+    for b in s.bytes() {
+        self.write_poll(b);
+    }
+    Ok(())
+  }
+  
+  fn write_char(&mut self, c: char) -> fmt::Result {
+    let mut buf = [0u8; 4];
+    let s = c.encode_utf8(&mut buf);
+    for b in s.bytes() {
+        self.write_poll(b);
+    }
+    Ok(())
+  }
+}

stage_3/src/ioport.rs

@@ -0,0 +1,23 @@
+use core::arch::asm;
+
+pub unsafe fn inb(port: u16) -> u8 {
+  let x: u8;
+  unsafe {
+    asm!(
+      "in al, dx",
+      in("dx") port,
+      lateout("al") x
+    );
+  }
+  x
+}
+
+pub unsafe fn outb(port: u16, x: u8) {
+  unsafe {
+    asm!(
+      "out dx, al",
+      in("al") x,
+      in("dx") port,
+    );
+  }
+}

stage_3/src/main.rs

@@ -4,9 +4,11 @@
 #![test_runner(crate::test_runner)]
 
 mod spin;
+mod ioport;
 mod vga;
+mod com;
 
-use core::{arch::{asm, global_asm}, panic::PanicInfo, fmt::Write};
+use core::{arch::{asm, global_asm}, fmt::Write, panic::PanicInfo, ptr, slice};
 
 global_asm!(include_str!("asm/trampoline.s"));
 
@@ -20,11 +22,26 @@ fn panic(info: &PanicInfo) -> ! {
   hlt()
 }
 
+const COM1_PORT: u16 = 0x3f8;
+
 #[unsafe(no_mangle)]
 pub extern "C" fn _start() -> ! {
   vga::vga_init();
 
+  let gdt_ptr = ptr::with_exposed_provenance::<u64>(0xc000);
+  let gdt_slice = unsafe { slice::from_raw_parts(gdt_ptr, 4) };
+
   vga_println!("hello from rust :)");
+  vga_println!("{:016x}", gdt_slice[0]);
+  vga_println!("{:016x}", gdt_slice[1]);
+  vga_println!("{:016x}", gdt_slice[2]);
+  vga_println!("{:016x}", gdt_slice[3]);
+  
+  let mut com = unsafe { com::Com::init(COM1_PORT) };
+
+  if let Ok(com) = &mut com {
+    writeln!(com, "hello serial").ok();
+  }
 
   hlt()
 }

xtask/src/mkimg.rs

@@ -1,8 +1,5 @@
 use crate::Context;
 
-const BLOCK_SIZE: u64 = 512;
-const PARTITION_ENTRY_SIZE: u64 = 128;
-
 // LBA 0: MBR
 // LBA 1: partition header
 // LBA 2..33: partition table entries