Merge pull request rust-osdev#28 from rust-osdev/lld-new

Use LLD for linking, fix page table zeroing, increase memory map size, improve errors

Author: phil-opp

Cargo.lock

@@ -28,17 +28,18 @@ SECTIONS {
     .bootloader :
     {
         /* first stage */
-        *(.boot)
+        *(.boot-first-stage)
 
-        /* second stage */
-        _second_stage_start_addr = .;
-        *(.second_stage)
+        /* rest of bootloader */
+        _rest_of_bootloader_start_addr = .;
+        *(.boot)
         *(.context_switch)
         *(.text .text.*)
         *(.rodata .rodata.*)
         *(.data .data.*)
+        *(.got)
         . = ALIGN(512);
-        _second_stage_end_addr = .;
+        _rest_of_bootloader_end_addr = .;
     }
 
     _kernel_info_block_start = .;

linker.ld

@@ -3,9 +3,11 @@ use core::ops::{Deref, DerefMut};
 
 const PAGE_SIZE: u64 = 4096;
 
+const MAX_MEMORY_MAP_SIZE: usize = 64;
+
 #[repr(C)]
 pub struct MemoryMap {
-    entries: [MemoryRegion; 32],
+    entries: [MemoryRegion; MAX_MEMORY_MAP_SIZE],
     // u64 instead of usize so that the structure layout is platform
     // independent
     next_entry_index: u64,
@@ -14,12 +16,14 @@ pub struct MemoryMap {
 impl MemoryMap {
     pub fn new() -> Self {
         MemoryMap {
-            entries: [MemoryRegion::empty(); 32],
+            entries: [MemoryRegion::empty(); MAX_MEMORY_MAP_SIZE],
             next_entry_index: 0,
         }
     }
 
     pub fn add_region(&mut self, region: MemoryRegion) {
+        assert!(self.next_entry_index() < MAX_MEMORY_MAP_SIZE,
+            "too many memory regions in memory map");
         self.entries[self.next_entry_index()] = region;
         self.next_entry_index += 1;
         self.sort();

src/bootinfo/memory_map.rs

@@ -1,4 +1,4 @@
-.section .second_stage, "awx"
+.section .boot, "awx"
 .intel_syntax noprefix
 .code16
 

src/memory_map.s renamed to src/e820.s

@@ -25,9 +25,11 @@ use x86_64::ux::u9;
 pub use x86_64::PhysAddr;
 use x86_64::VirtAddr;
 
-global_asm!(include_str!("boot.s"));
-global_asm!(include_str!("second_stage.s"));
-global_asm!(include_str!("memory_map.s"));
+global_asm!(include_str!("stage_1.s"));
+global_asm!(include_str!("stage_2.s"));
+global_asm!(include_str!("e820.s"));
+global_asm!(include_str!("stage_3.s"));
+global_asm!(include_str!("stage_4.s"));
 global_asm!(include_str!("context_switch.s"));
 
 extern "C" {

src/main.rs

@@ -1,8 +1,11 @@
-.section .boot, "awx"
+.section .boot-first-stage, "awx"
 .global _start
 .intel_syntax noprefix
 .code16
 
+# This stage initializes the stack, enables the A20 line, loads the rest of
+# the bootloader from disk, and jumps to stage_2.
+
 _start:
     # zero segment registers
     xor ax, ax
@@ -16,7 +19,6 @@ _start:
     # instructions like lodsb)
     cld
 
-
     # initialize stack
     mov sp, 0x7c00
 
@@ -35,7 +37,7 @@ enter_protected_mode:
     push ds
     push es
 
-    lgdt [gdtinfo]
+    lgdt [gdt32info]
 
     mov eax, cr0
     or al, 1    # set protected mode bit
@@ -44,7 +46,7 @@ enter_protected_mode:
     jmp protected_mode                # tell 386/486 to not crash
 
 protected_mode:
-    mov bx, 0x8
+    mov bx, 0x10
     mov ds, bx # set data segment
     mov es, bx # set extra segment
 
@@ -70,15 +72,15 @@ check_int13h_extensions:
     int 0x13
     jc no_int13h_extensions
 
-load_second_stage_from_disk:
-    lea eax, _second_stage_start_addr
+load_rest_of_bootloader_from_disk:
+    lea eax, _rest_of_bootloader_start_addr
 
     # start of memory buffer
     mov [dap_buffer_addr], ax
 
     # number of disk blocks to load
     lea ebx, _kernel_info_block_end
-    sub ebx, eax # second stage end - second stage start
+    sub ebx, eax # end - start
     shr ebx, 9 # divide by 512 (block size)
     mov [dap_blocks], bx
 
@@ -91,10 +93,10 @@ load_second_stage_from_disk:
     lea si, dap
     mov ah, 0x42
     int 0x13
-    jc second_stage_load_failed
+    jc rest_of_bootloader_load_failed
 
 jump_to_second_stage:
-    lea eax, second_stage
+    lea eax, [stage_2]
     jmp eax
 
 spin:
@@ -174,29 +176,33 @@ no_int13h_extensions:
     lea si, no_int13h_extensions_str
     jmp error
 
-second_stage_load_failed:
-    lea si, second_stage_load_failed_str
-    jmp error
-
-kernel_load_failed:
-    lea si, kernel_load_failed_str
+rest_of_bootloader_load_failed:
+    lea si, rest_of_bootloader_load_failed_str
     jmp error
 
 boot_start_str: .asciz "Booting (first stage)..."
-second_stage_start_str: .asciz "Booting (second stage)..."
 error_str: .asciz "Error: "
 no_cpuid_str: .asciz "No CPUID support"
 no_int13h_extensions_str: .asciz "No support for int13h extensions"
-second_stage_load_failed_str: .asciz "Failed to load second stage of bootloader"
+rest_of_bootloader_load_failed_str: .asciz "Failed to load rest of bootloader"
 
-gdtinfo:
-   .word gdt_end - gdt - 1  # last byte in table
-   .word gdt                # start of table
+gdt32info:
+   .word gdt32_end - gdt32 - 1  # last byte in table
+   .word gdt32                  # start of table
 
-gdt:
+gdt32:
     # entry 0 is always unused
     .quad 0
-flatdesc:
+codedesc:
+    .byte 0xff
+    .byte 0xff
+    .byte 0
+    .byte 0
+    .byte 0
+    .byte 0x9a
+    .byte 0xcf
+    .byte 0
+datadesc:
     .byte 0xff
     .byte 0xff
     .byte 0
@@ -205,7 +211,7 @@ flatdesc:
     .byte 0x92
     .byte 0xcf
     .byte 0
-gdt_end:
+gdt32_end:
 
 dap: # disk access packet
     .byte 0x10 # size of dap

src/boot.s renamed to src/stage_1.s

@@ -0,0 +1,102 @@
+.section .boot, "awx"
+.intel_syntax noprefix
+.code16
+
+# This stage sets the target operating mode, loads the kernel from disk,
+# creates an e820 memory map, enters protected mode, and jumps to the
+# third stage.
+
+second_stage_start_str: .asciz "Booting (second stage)..."
+kernel_load_failed_str: .asciz "Failed to load kernel from disk"
+
+kernel_load_failed:
+    lea si, [kernel_load_failed_str]
+    call println
+kernel_load_failed_spin:
+    jmp kernel_load_failed_spin
+
+stage_2:
+    lea si, [second_stage_start_str]
+    call println
+
+set_target_operating_mode:
+    # Some BIOSs assume the processor will only operate in Legacy Mode. We change the Target
+    # Operating Mode to "Long Mode Target Only", so the firmware expects each CPU to enter Long Mode
+    # once and then stay in it. This allows the firmware to enable mode-specifc optimizations.
+    # We save the flags, because CF is set if the callback is not supported (in which case, this is
+    # a NOP)
+    pushf
+    mov ax, 0xec00
+    mov bl, 0x2
+    int 0x15
+    popf
+
+load_kernel_from_disk:
+    # start of memory buffer
+    lea eax, _kernel_buffer
+    mov [dap_buffer_addr], ax
+
+    # number of disk blocks to load
+    mov word ptr [dap_blocks], 1
+
+    # number of start block
+    lea eax, _kernel_start_addr
+    lea ebx, _start
+    sub eax, ebx
+    shr eax, 9 # divide by 512 (block size)
+    mov [dap_start_lba], eax
+
+    # destination address
+    mov edi, 0x400000
+
+    # block count
+    mov ecx, _kib_kernel_size
+    add ecx, 511 # align up
+    shr ecx, 9
+
+load_next_kernel_block_from_disk:
+    # load block from disk
+    lea si, dap
+    mov ah, 0x42
+    int 0x13
+    jc kernel_load_failed
+
+    # copy block to 2MiB
+    push ecx
+    push esi
+    mov ecx, 512 / 4
+    # move with zero extension
+    # because we are moving a word ptr
+    # to esi, a 32-bit register.
+    movzx esi, word ptr [dap_buffer_addr]
+    # move from esi to edi ecx times.
+    rep movsd [edi], [esi]
+    pop esi
+    pop ecx
+
+    # next block
+    mov eax, [dap_start_lba]
+    add eax, 1
+    mov [dap_start_lba], eax
+
+    sub ecx, 1
+    jnz load_next_kernel_block_from_disk
+
+create_memory_map:
+    lea di, es:[_memory_map]
+    call do_e820
+
+enter_protected_mode_again:
+    cli
+    lgdt [gdt32info]
+    mov eax, cr0
+    or al, 1    # set protected mode bit
+    mov cr0, eax
+
+    push 0x8
+    lea eax, [stage_3]
+    push eax
+    retf
+
+spin32:
+    jmp spin32