diff options
Diffstat (limited to 'src/boot/boot32.s')
| -rw-r--r-- | src/boot/boot32.s | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/src/boot/boot32.s b/src/boot/boot32.s new file mode 100644 index 0000000..5650422 --- /dev/null +++ b/src/boot/boot32.s @@ -0,0 +1,137 @@ +.global _start +.extern long_mode_start + +.section .text +.code32 + +/* Entry point. It puts the machine into a consistent state and starts long mode. */ +_start: + mov $0x80000, %esp // Setup the stack. + + call boot_check_multiboot + call boot_check_cpuid + call boot_check_long_mode + + call boot_setup_page_tables + call boot_enable_paging + + lgdt (boot_gdtdesc) + jmpl $0x8, $boot_long_mode_start + hlt + +boot_check_multiboot: + cmp $0x36d76289, %eax + jne .boot_no_multiboot + ret +.boot_no_multiboot: + mov $'M', %al + jmp boot_error + +boot_check_cpuid: + pushfd + pop %eax + mov %eax, %ecx + xor $(1 << 21), %eax + push %eax + popfd + pushfd + pop %eax + push %ecx + popfd + cmp %eax, %ecx + je .boot_no_cpuid + ret +.boot_no_cpuid: + mov $'C', %al + jmp boot_error + +boot_check_long_mode: + mov $0x80000000, %eax + cpuid + cmp $0x80000001, %eax + jb .boot_no_long_mode + + mov $0x80000001, %eax + cpuid + test $(1 << 29), %edx + jz .boot_no_long_mode + + ret +.boot_no_long_mode: + mov $'L', %al + jmp boot_error + +boot_setup_page_tables: + mov $page_table_l3, %eax + or $0b11 , %eax /* present, writable */ + mov %eax, (page_table_l4) + + mov $page_table_l2, %eax + or $0b11, %eax /* present, writable */ + mov %eax, (page_table_l3) + + mov $0, %ecx /* counter */ +.boot_pages_loop: + + mov $0x200000, %eax /* 2MiB */ + mul %ecx + or $0b10000011, %eax /* present, writable, huge page */ + mov %eax, +page_table_l2(,%ecx,8) + + inc %ecx /* increment counter */ + cmp $512, %ecx /* checks if the whole table is mapped */ + jne .boot_pages_loop /* if not, continue */ + + ret + +boot_enable_paging: + /* pass page table location to cpu */ + mov $page_table_l4, %eax + mov %eax, %cr3 + + /* enable PAE */ + mov %cr4, %eax + or $(1 << 5), %eax + mov %eax, %cr4 + + /* enable long mode */ + mov $0xC0000080, %ecx + rdmsr + or $(1 << 8), %eax + wrmsr + + /* enable paging */ + mov %cr0, %eax + or $(1 << 31), %eax + mov %eax, %cr0 + + ret + +boot_error: + /* print in VGA "ERR: X" where X is the error code */ + movl $0x4f524f45, 0xb8000 + movl $0x4f3a4f52, 0xb8004 + movl $0x4f204f20, 0xb8008 + movb %al, 0xb800a + hlt + +.section .bss +.align 4096 +page_table_l4: + .skip 4096 +page_table_l3: + .skip 4096 +page_table_l2: + .skip 4096 +stack_bottom: + .skip 4096 * 4 +stack_top: + +.section .rodata +.p2align 2 /* force 4 byte alignment */ +boot_gdt64: + .quad 0 /* zero entry */ + .quad (1 << 43) | (1 << 44) | (1 << 47) | (1 << 53) /* code segment */ +boot_gdtdesc: + .word (boot_gdtdesc - boot_gdt64 - 1) /* sizeof(gdt) - 1 */ + .long boot_gdt64 /* address gdt */
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