# along with this program. If not, see <https://www.gnu.org/licenses/>.
# this is the second-stage boot loader
+# plus some other code that needs to run below 1mb (int86 implementation).
+
.code16
- .section .boot2,"a"
+ .section .boot2,"ax"
.set main_load_addr, 0x100000
# 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
- mov $0x13, %ax
- int $0x10
+ #mov $0x13, %ax
+ #int $0x10
# load initial GDT
lgdt (gdt_lim)
push %ecx
call read_track
- mov buffer, %eax
- call print_num
- mov $10, %al
- call putchar
+ # debug: print the first 32bits of the track
+ #mov buffer, %eax
+ #call print_num
+ #mov $10, %al
+ #call putchar
# copy to high memory
mov $buffer, %esi
# just in case we were loaded from floppy, turn all floppy motors off
mov $0x3f2, %dx
in %dx, %al
- and $0xf0, %al
+ and $0xf, %al
out %al, %dx
mov $10, %ax
call putchar
- # DBG
- hlt
-
ret
rdtrk_msg: .asciz "Reading track: "
rdcyl_msg: .asciz " - cyl: "
rdhead_msg: .asciz " head: "
rdsect_msg: .asciz " start sect: "
+rdlast_msg: .asciz " ... "
+rdok_msg: .asciz "OK\n"
+rdfail_msg: .asciz "failed\n"
read_retries: .short 0
call putstr
mov trk_sect, %eax
call print_num
- mov $10, %al
- call putchar
+ mov $rdlast_msg, %esi
+ call putstr
# start sector (1-based) in cl[0, 5]
mov trk_sect, %al
jmp read_try
read_fail:
+ mov $rdfail_msg, %esi
+ call putstr
jmp abort_read
read_ok:
- mov $35, %ax
- call putchar
+ mov $rdok_msg, %esi
+ call putstr
# reset es to 0 before returning
xor %ax, %ax
jmp 0b
-
# better print routines, since we're not constrainted by the 512b of
# the boot sector.
+ .global cursor_x
+ .global cursor_y
cursor_x: .long 0
cursor_y: .long 0
putchar:
- pusha
+ pushal
call ser_putchar
cmp $10, %al
jnz 1f
call video_newline
-1: popa
+1: popal
ret
# expects string pointer in esi
# expects number in eax
print_num:
# save registers
- pusha
+ pushal
mov $numbuf + 16, %esi
movb $0, (%esi)
call putstr
# restore regs
- popa
+ popal
ret
0: ret
scrollup:
- pusha
+ pushal
# move 80 * 24 lines from b80a0 -> b8000
mov $0xb8000, %edi
mov $0xb80a0, %esi
xor %eax, %eax
mov $40, %ecx
addr32 rep stosl
- popa
+ popal
ret
clearscr:
numbuf: .space 16
+
+detect_memory:
+ mov $memdet_e820_msg, %esi
+ call putstr
+ call detect_mem_e820
+ jnc memdet_done
+ mov $rdfail_msg, %esi
+ call putstr
+
+ mov $memdet_e801_msg, %esi
+ call putstr
+ call detect_mem_e801
+ jnc memdet_done
+ mov $rdfail_msg, %esi
+ call putstr
+
+ mov $memdet_88_msg, %esi
+ call putstr
+ call detect_mem_88
+ jnc memdet_done
+ mov $rdfail_msg, %esi
+ call putstr
+
+ # just panic...
+ mov $memdet_fail_msg, %esi
+ call putstr
+0: hlt
+ jmp 0b
+
+memdet_done:
+ mov $rdok_msg, %esi
+ call putstr
+ ret
+
+memdet_fail_msg: .ascii "Failed to detect available memory!\n"
+ .ascii "Please file a bug report: https://github.com/jtsiomb/pcboot/issues\n"
+ .asciz " or contact me through email: nuclear@member.fsf.org\n"
+memdet_e820_msg: .asciz "Detecting RAM (BIOS 15h/0xe820)... "
+memdet_e801_msg: .asciz "Detecting RAM (BIOS 15h/0xe801)... "
+memdet_88_msg: .asciz "Detecting RAM (BIOS 15h/0x88, max 64mb)... "
+
+ # detect extended memory using BIOS call 15h/e820
+detect_mem_e820:
+ movl $0, boot_mem_map_size
+
+ mov $buffer, %edi
+ xor %ebx, %ebx
+ mov $0x534d4150, %edx
+
+e820_looptop:
+ mov $0xe820, %eax
+ mov $24, %ecx
+ int $0x15
+ jc e820_fail
+ cmp $0x534d4150, %eax
+ jnz e820_fail
+
+ # skip areas starting above 4GB as we won't be able to use them
+ cmpl $0, 4(%edi)
+ jnz e820_skip
+
+ # only care for type 1 (usable ram), otherwise ignore
+ cmpl $1, 16(%edi)
+ jnz e820_skip
+
+ 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)
+
+ # skip areas with 0 size (also clamp size to 4gb)
+ # test high 32bits
+ cmpl $0, 12(%edi)
+ jz e820_highzero
+ # high part is non-zero, make low part ffffffff
+ xor %eax, %eax
+ not %eax
+ jmp 0f
+
+e820_highzero:
+ # if both high and low parts are zero, ignore
+ mov 8(%edi), %eax
+ cmpl $0, %eax
+ jz e820_skip
+
+0: mov %eax, 4(%esi,%ebp,8)
+ incl boot_mem_map_size
+
+e820_skip:
+ # terminate the loop if ebx was reset to 0
+ cmp $0, %ebx
+ jz e820_done
+ jmp e820_looptop
+
+e820_done:
+ clc
+ ret
+
+e820_fail:
+ # if size > 0, then it's not a failure, just the end
+ cmpl $0, boot_mem_map_size
+ jnz e820_done
+
+ stc
+ ret
+
+
+ # detect extended memory using BIOS call 15h/e801
+detect_mem_e801:
+ mov $boot_mem_map, %esi
+ mov boot_mem_map_size, %ebp
+ movl $0, (%ebp)
+
+ xor %cx, %cx
+ xor %dx, %dx
+ mov $0xe801, %ax
+ int $0x15
+ jc e801_fail
+
+ cmp $0, %cx
+ jnz 0f
+ cmp $0, %ax
+ jz e801_fail
+ mov %ax, %cx
+ mov %bx, %dx
+
+0: movl $0x100000, (%esi)
+ movzx %cx, %eax
+ # first size is in KB, convert to bytes
+ shl $10, %eax
+ jnc 0f
+ # overflow means it's >4GB, clamp to 4GB
+ mov $0xffffffff, %eax
+0: mov %eax, 4(%esi)
+ incl boot_mem_map_size
+ cmp $0, %dx
+ jz e801_done
+ movl $0x1000000, 8(%esi)
+ movzx %dx, %eax
+ # second size is in 64kb blocks, convert to bytes
+ shl $16, %eax
+ jnc 0f
+ # overflow means it's >4GB, clamp to 4GB
+ mov $0xffffffff, %eax
+0: mov %eax, 12(%esi)
+ incl boot_mem_map_size
+e801_done:
+ clc
+ ret
+e801_fail:
+ stc
+ ret
+
+detect_mem_88:
+ # reportedly some BIOS implementations fail to clear CF on success
+ clc
+ mov $0x88, %ah
+ int $0x15
+ jc x88_fail
+
+ cmp $0, %ax
+ jz x88_fail
+
+ # ax has size in KB, convert to bytes in eax
+ and $0xffff, %eax
+ shl $10, %eax
+
+ mov $boot_mem_map, %esi
+ movl $0x100000, (%esi)
+ mov %eax, 4(%esi)
+
+ movl $1, boot_mem_map_size
+ clc
+ ret
+
+x88_fail:
+ stc
+ ret
+
+
+ .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
+ # with sidt, so that it can be restored before returning
+ .short 0
+saved_idtr:
+idtlim: .short 0
+idtaddr:.long 0
+ # real mode IDTR pseudo-descriptor pointing to the IVT at addr 0
+ .short 0
+rmidt: .short 0x3ff
+ .long 0
+
+saved_esp: .long 0
+saved_ebp: .long 0
+saved_eax: .long 0
+saved_es: .word 0
+saved_ds: .word 0
+saved_flags: .word 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:
+ .code16
+ # disable protection
+ mov %cr0, %eax
+ and $0xfffe, %ax
+ mov %eax, %cr0
+ # load cs <- 0
+ ljmp $0,$0f
+0: # zero data segments
+ xor %ax, %ax
+ mov %ax, %ds
+ mov %ax, %es
+ mov %ax, %ss
+ nop
+
+ # load registers from the int86regs struct
+ # point esp to the regs struct to load registers with popa/popf
+ mov %esp, saved_esp
+ mov %ebp, saved_ebp
+ mov 12(%ebp), %esp
+ popal
+ popfw
+ pop %es
+ pop %ds
+ # ignore fs and gs for now, don't think I'm going to need them
+ mov saved_esp, %esp
+
+ # move to the real-mode stack, accessible from ss=0
+ # just in case the BIOS call screws up our unreal mode
+ mov $0x7be0, %esp
+
+ # call 16bit interrupt
+int_op: int $0
+ # BIOS call might have enabled interrupts, cli for good measure
+ cli
+
+ # save all registers that we'll clobber before having the
+ # chance to populate the int86regs structure
+ mov %eax, saved_eax
+ mov %ds, saved_ds
+ mov %es, saved_es
+ pushfw
+ pop %ax
+ mov %ax, saved_flags
+
+ # re-enable protection
+ mov %cr0, %eax
+ or $1, %ax
+ mov %eax, %cr0
+ # long jump to load code selector for 32bit code (1)
+ ljmp $0x8,$0f
+0:
+ .code32
+ # set data selector (2) to all segment regs
+ mov $0x10, %ax
+ mov %ax, %ds
+ mov %ax, %es
+ mov %ax, %ss
+ nop
+
+ # point the esp to our regs struct, to fill it with pusha/pushf
+ mov saved_ebp, %ebp
+ mov 12(%ebp), %esp
+ add $38, %esp
+ mov saved_ds, %ax
+ pushw %ax
+ mov saved_es, %ax
+ pushw %ax
+ mov saved_flags, %ax
+ pushw %ax
+ mov saved_eax, %eax
+ pushal
+ mov saved_esp, %esp
+
+ # restore 32bit interrupt descriptor table
+ lidt (saved_idtr)
+ sti
+ popal
+ pop %ebp
+ ret
+
+
+ # buffer used by the track loader ... to load tracks.
.align 16
buffer:
+ .global low_mem_buffer
+low_mem_buffer:
projects / bootcensus / blobdiff