Rehaul the memory map

[nameless-os.git] / boot / x86 / mbr.s

diff --git a/boot/x86/mbr.s b/boot/x86/mbr.s
index 8089b2f27e244bbbe1aeecb1477f691d77152b77..b5d01c94f6ea86ccffd0752714db580280b6abce 100644 (file)
--- a/boot/x86/mbr.s
+++ b/boot/x86/mbr.s
@@ -5,13 +5,13 @@ cpu 686
 org 0x600
 
 _start:
-       cli
+       cli ; we really don't want to be interrupted during relocation
        ; set up segment registers
        xor ax, ax
        mov ds, ax
        mov es, ax
        mov ss, ax
-       mov sp, 0x7c00 ; just under the soon-to-be-loaded VBR, should be more than sufficient space
+       mov sp, 0xfe00 ; just under the soon-to-be-loaded VBR, should be more than sufficient space
 
        ; perform self-relocation
        cld
@@ -27,55 +27,51 @@ real_start:
        call check_int13_ext
        mov byte [BOOT_DRIVE], dl
        ; look for active partition
-       mov bx, part_1
+       mov si, part_1
        mov cx, 4
        .check_part_loop:
-               mov al, [bx]
+               mov al, [si]
                test al, 0x80
                jnz .part_found
-               add bx, 16
+               add si, 16
                loop .check_part_loop
                .error:
                        mov si, no_os
                        call print
-                       cli
                        hlt
                        jmp short $-1
        .part_found:
                ; look for any other active partitions, if they exist the partition table is invalid
                cmp cx, 0
                je .load_vbr
-               push bx
+               push si 
        .look_other_loop:
-               add bx, 16
-               mov al, [bx]
+               add si, 16
+               mov al, [si]
                test al, 0x80
                jnz .invalid_mbr
                loop .look_other_loop
        .load_vbr:
                ; load active partition's VBR
-               pop bx
-               mov ax, 0x7c0
-               mov edx, [bx+0x8]
-               push bx ; save pointer to partition table entry
+               pop si
+               mov ax, 0xfe0
+               add si, 8
+               mov edx, [si]
                xor bx, bx
                call read_sector
                ; check is the VBR bootable (ends with 0x55 0xaa), if not halt
-               cmp word [0x7dfe], 0xaa55
+               cmp word [0xfffe], 0xaa55
                jne .not_bootable
                mov dl, [BOOT_DRIVE]
-               pop si ; hand off partition table entry to VBR
-               jmp 0x7c00
+               call 0xfe00
                .not_bootable:
                        mov si, no_os
                        call print
-                       cli
                        hlt
                        jmp short $-1
        .invalid_mbr:
                mov si, invalid_mbr
                call print
-               cli
                hlt
                jmp short $-1
 check_int13_ext:
@@ -92,7 +88,6 @@ check_int13_ext:
        .no_ext:
                mov si, no_int13_ext
                call print
-               cli
                hlt
                jmp short $-1
 
@@ -119,7 +114,6 @@ read_sector:
        .error:
                mov si, read_fail
                call print
-               cli
                hlt
                jmp short $-1