wrote a basic bootloader

2025-02-25 01:14:52 +00:00
commit 012b0454ed
36 changed files with 1667 additions and 0 deletions
@@ -0,0 +1,83 @@
+.section .efi.text, "ax"
+.global _start
+.code64  // UEFI is already in 64-bit protected mode
+
+_start:
+    // Save UEFI parameters
+    mov %rcx, uefi_image_handle
+    mov %rdx, uefi_system_table
+
+    // Get memory map
+    call get_memory_map
+
+    // Exit boot services
+    mov uefi_image_handle, %rcx
+    mov memory_map_key, %rdx
+    call exit_boot_services
+    
+    // Disable interrupts
+    cli
+
+    // Load GDT for long mode
+    lgdt gdt64_pointer(%rip)
+
+    // Setup page tables (identity map first 2MB + map kernel to higher half)
+    call setup_page_tables
+
+    // Enable PAE
+    mov %cr4, %rax
+    or $(1 << 5), %rax
+    mov %rax, %cr4
+
+    // Set long mode bit
+    mov $0xC0000080, %ecx
+    rdmsr
+    or $(1 << 8), %eax
+    wrmsr
+
+    // Enable paging
+    mov %cr0, %rax
+    or $0x80000000, %rax
+    mov %rax, %cr0
+
+    // Long jump to higher half kernel
+    lea higher_half(%rip), %rax
+    jmp *%rax
+
+.align 8
+higher_half:
+    // Now in long mode at higher half
+    // Setup stack and jump to Rust code
+    mov $kernel_stack_top, %rsp
+    call kmain
+
+// GDT for long mode
+.align 16
+gdt64:
+    .quad 0                    // Null descriptor
+    .quad 0x00AF9A000000FFFF  // Code segment
+    .quad 0x00CF92000000FFFF  // Data segment
+
+gdt64_pointer:
+    .word gdt64_pointer - gdt64 - 1
+    .quad gdt64
+
+.section .efi.data, "aw"
+uefi_image_handle:  .quad 0
+uefi_system_table:  .quad 0
+memory_map_key:     .quad 0
+
+.section .bss
+.align 4096
+kernel_stack_bottom:
+    .skip 16384  // 16 KB stack
+kernel_stack_top:
+
+// Page tables
+.align 4096
+pml4_table:
+    .skip 4096
+pdpt_table:
+    .skip 4096
+pd_table:
+    .skip 4096