# enable A20 address line
call enable_a20
+ # detect available memory
+ call detect_memory
+
# load the whole program into memory starting at 1MB
call load_main
numbuf: .space 16
-# this is not boot loader code. It's called later on by the main
-# kernel code in 32bit protected mode. It's placed here because
-# it needs to be in base memory as it returns and runs in real mode.
+ # sets the carry flag on failure
+detect_memory:
+ mov $buffer, %edi
+ xor %ebx, %ebx
+ mov $0x534d4150, %edx
+
+memdet_looptop:
+ mov $0xe820, %eax
+ mov $24, %ecx
+ int $0x15
+ jc memdet_fail
+ cmp $0x534d4150, %eax
+ jnz memdet_fail
+
+ mov buffer, %eax
+ mov $boot_mem_map, %esi
+ mov boot_mem_map_size, %ebp
+ # again, that's [ebp * 8 + esi]
+ mov %eax, (%esi,%ebp,8)
+
+ # only care for type 1 (usable ram), otherwise ignore
+ cmpl $1, 16(%edi)
+ jnz memdet_skip
+
+ # skip areas with 0 size (also clamp size to 4gb)
+ # test high 32bits
+ cmpl $0, 12(%edi)
+ jz memdet_highzero
+ # high part is non-zero, make low part ffffffff
+ xor %eax, %eax
+ not %eax
+ jmp 0f
+
+memdet_highzero:
+ # if both high and low parts are zero, ignore
+ mov 8(%edi), %eax
+ cmpl $0, %eax
+ jz memdet_skip
+
+0: mov %eax, 4(%esi,%ebp,8)
+ incl boot_mem_map_size
+memdet_skip:
+ # terminate the loop if ebx was reset to 0
+ cmp $0, %ebx
+ jz memdet_done
+ jmp memdet_looptop
+
+memdet_done:
+ ret
+
+memdet_fail:
+ # if size > 0, then it's not a failure, just the end
+ cmpl $0, boot_mem_map_size
+ jnz memdet_done
+
+ # just panic...
+ mov $memdet_fail_msg, %esi
+ call putstr
+0: hlt
+ jmp 0b
+
+memdet_fail_msg: .asciz "Failed to detect available memory!\n"
+
+ .global boot_mem_map_size
+boot_mem_map_size: .long 0
+ .global boot_mem_map
+boot_mem_map: .space 128
+
+
+# this is not boot loader code. It's called later on by the main kernel
+# code in 32bit protected mode. It's placed here because it needs to be
+# located in base memory as it returns and runs in real mode.
.code32
.align 4
# place to save the protected mode IDTR pseudo-descriptor
rmidt: .short 0x3ff
.long 0
- # drop back to unreal mode to set video mode
- .global set_mode13h
-set_mode13h:
+saved_esp: .long 0
+saved_ebp: .long 0
+
+ # drop back to unreal mode to call 16bit interrupt
+ .global int86
+int86:
+ push %ebp
+ mov %esp, %ebp
pushal
cli
# save protected mode IDTR and replace it with the real mode vectors
sidt (saved_idtr)
lidt (rmidt)
+ # modify the int instruction do this here before the
+ # cs-load jumps, to let them flush the instruction cache
+ mov $int_op, %ebx
+ movb 8(%ebp), %al
+ movb %al, 1(%ebx)
+
# long jump to load code selector for 16bit code (6)
ljmp $0x30,$0f
0:
mov %ax, %ss
nop
- # switch video mode by calling the video bios
- mov $0x13, %ax
- int $0x10
+ # load registers from the int86regs struct
+ mov %esp, saved_esp
+ mov %ebp, saved_ebp
+ mov 12(%ebp), %esp
+ popal
+ mov saved_esp, %esp
+
+ # call 16bit interrupt
+int_op: int $0
+
+ mov saved_ebp, %ebp
+ mov 12(%ebp), %esp
+ add $34, %esp
+ pushfw
+ pushal
+ mov saved_esp, %esp
# re-enable protection
mov %cr0, %eax
lidt (saved_idtr)
sti
popal
+ pop %ebp
ret