+# pcboot - bootable PC demo/game kernel
+# Copyright (C) 2018 John Tsiombikas <nuclear@member.fsf.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY, without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
+
# this is the second-stage boot loader
.code16
- .section .boot2,"a"
+ .section .boot2,"ax"
+
+ .set main_load_addr, 0x100000
+
+ # make sure any BIOS call didn't re-enable interrupts
+ cli
+
+ # enter unreal mode
+ call unreal
+
+ movb $10, %al
+ call ser_putchar
+
+ call clearscr
+
+ # enable A20 address line
+ call enable_a20
+
+ # load the whole program into memory starting at 1MB
+ call load_main
+
+ #mov $0x13, %ax
+ #int $0x10
+
+ # load initial GDT
+ lgdt (gdt_lim)
+ # load initial IDT
+ lidt (idt_lim)
+
+ # enter protected mode for the first time
+ mov %cr0, %eax
+ or $1, %eax
+ mov %eax, %cr0
+ # inter-segment jump to set cs selector to segment 1
+ ljmp $0x8,$0f
+
+ .code32
+ # set all data selectors to segment 2
+0: mov $0x10, %ax
+ mov %ax, %ds
+ mov %ax, %ss
+ mov %ax, %es
+ mov %ax, %gs
+ mov %ax, %fs
+
+ jmp main_load_addr
+
+ cli
+0: hlt
+ jmp 0b
- mov $0x13, %ax
- int $0x10
- pushw $63
- pushw $63
- pushw $0
- pushw $0xff
- call set_palette
- add $8, %sp
- pushw $0xa000
- pop %es
- xor %di, %di
- mov $16000, %ecx
- mov $0xffffffff, %eax
- rep stosl
+ .align 4
+gdt_lim: .word 23
+gdt_base:.long gdt
+ .align 4
+idt_lim: .word 111
+idt_base:.long idt
+
+
+ .align 8
+gdt: # 0: null segment
+ .long 0
+ .long 0
+ # 1: code - base:0, lim:4g, G:4k, 32bit, avl, pres|app, dpl:0, type:code/non-conf/rd
+ .long 0x0000ffff
+ .long 0x00cf9a00
+ # 2: data - base:0, lim:4g, G:4k, 32bit, avl, pres|app, dpl:0, type:data/rw
+ .long 0x0000ffff
+ .long 0x00cf9200
+
+
+ .align 8
+idt: .space 104
+ # trap gate 13: general protection fault
+ .short prot_fault
+ .short 0x8
+ # type: trap, present, default
+ .short 0x8f00
+ .short 0
+
+gpf_msg: .asciz "GP fault "
+
+prot_fault:
+ mov (%esp), %eax
+ shr $3, %eax
+ call print_num
+ mov $64, %al
+ call putchar
+ mov 4(%esp), %eax
+ call print_num
+ mov $10, %al
+ call putchar
hlt
-set_palette:
- mov %sp, %bp
- mov $0x3c8, %dx
- movw 2(%bp), %ax
- outb %al, %dx
- inc %dx
- movw 4(%bp), %ax
- outb %al, %dx
- movw 6(%bp), %ax
- outb %al, %dx
- movw 8(%bp), %ax
- outb %al, %dx
+ .code16
+unreal:
+ # use the same GDT above, will use data segment: 2
+ lgdt (gdt_lim)
+
+ mov %cr0, %eax
+ or $1, %ax
+ mov %eax, %cr0
+ jmp 0f
+
+0: mov $0x10, %ax
+ mov %ax, %ds
+ mov %ax, %es
+ mov %ax, %fs
+ mov %ax, %gs
+ mov %ax, %ss
+
+ mov %cr0, %eax
+ and $0xfffe, %ax
+ mov %eax, %cr0
+
+ xor %ax, %ax
+ mov %ax, %ds
+ mov %ax, %es
+ mov %ax, %fs
+ mov %ax, %gs
+ mov %ax, %ss
+ ret
+
+mainsz_msg: .asciz "Main program size: "
+mainsz_msg2: .asciz " ("
+mainsz_msg3: .asciz " sectors)\n"
+
+first_sect: .long 0
+sect_left: .long 0
+cur_track: .long 0
+trk_sect: .long 0
+dest_ptr: .long 0
+
+load_main:
+ movl $main_load_addr, dest_ptr
+
+ # calculate first sector
+ mov $_boot2_size, %eax
+ add $511, %eax
+ shr $9, %eax
+ # add 1 to account for the boot sector
+ inc %eax
+ mov %eax, first_sect
+
+ # calculate the first track (first_sect / sect_per_track)
+ movzxw sect_per_track, %ecx
+ xor %edx, %edx
+ div %ecx
+ mov %eax, cur_track
+ # remainder is sector within track
+ mov %edx, trk_sect
+
+ mov $mainsz_msg, %esi
+ call putstr
+ mov $_main_size, %eax
+ mov %eax, %ecx
+ call print_num
+
+ mov $mainsz_msg2, %esi
+ call putstr
+
+ # calculate sector count
+ add $511, %eax
+ shr $9, %eax
+ mov %eax, sect_left
+
+ call print_num
+ mov $mainsz_msg3, %esi
+ call putstr
+
+ # read a whole track into the buffer (or partial first track)
+ldloop:
+ movzxw sect_per_track, %ecx
+ sub trk_sect, %ecx
+ push %ecx
+ call read_track
+
+ # 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
+ mov dest_ptr, %edi
+ mov (%esp), %ecx
+ shl $9, %ecx
+ add %ecx, dest_ptr
+ shr $2, %ecx
+ addr32 rep movsl
+
+ incl cur_track
+ # other than the first track which might be partial, all the rest start from 0
+ movl $0, trk_sect
+
+ pop %ecx
+ sub %ecx, sect_left
+ ja ldloop
+
+ # the BIOS might have enabled interrupts
+ cli
+
+ # just in case we were loaded from floppy, turn all floppy motors off
+ mov $0x3f2, %dx
+ in %dx, %al
+ and $0xf0, %al
+ out %al, %dx
+
+ mov $10, %ax
+ call putchar
+
+ 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
+
+ .set drive_number, 0x7bec
+read_track:
+ # set es to the start of the destination buffer to allow reading in
+ # full 64k chunks if necessary
+ mov $buffer, %bx
+ shr $4, %bx
+ mov %bx, %es
+ xor %ebx, %ebx
+
+ movw $3, read_retries
+
+read_try:
+ # print track
+ mov $rdtrk_msg, %esi
+ call putstr
+ mov cur_track, %eax
+ call print_num
+ mov $rdcyl_msg, %esi
+ call putstr
+
+ # calc cylinder (cur_track / num_heads) and head (cur_track % num_heads)
+ mov cur_track, %eax
+ movzxw num_heads, %ecx
+ xor %edx, %edx
+ div %ecx
+
+ # print cylinder
+ push %eax
+ call print_num
+ # print head
+ mov $rdhead_msg, %esi
+ call putstr
+ movzx %dx, %eax
+ call print_num
+ pop %eax
+
+ # head in dh
+ mov %dl, %dh
+
+ # cylinder low byte at ch and high bits at cl[7, 6]
+ mov %al, %ch
+ mov %ah, %cl
+ and $3, %cl
+ ror $2, %cl
+
+ # print start sector
+ mov $rdsect_msg, %esi
+ call putstr
+ mov trk_sect, %eax
+ call print_num
+ mov $rdlast_msg, %esi
+ call putstr
+
+ # start sector (1-based) in cl[0, 5]
+ mov trk_sect, %al
+ inc %al
+ and $0x3f, %al
+ or %al, %cl
+
+ # number of sectors in al
+ mov 2(%esp), %ax
+ # call number (2) in ah
+ mov $2, %ah
+ # drive number in dl
+ movb drive_number, %dl
+ int $0x13
+ jnc read_ok
+
+ # abort after 3 attempts
+ decw read_retries
+ jz read_fail
+
+ # error, reset controller and retry
+ xor %ah, %ah
+ int $0x13
+ jmp read_try
+
+read_fail:
+ mov $rdfail_msg, %esi
+ call putstr
+ jmp abort_read
+
+read_ok:
+ mov $rdok_msg, %esi
+ call putstr
+
+ # reset es to 0 before returning
+ xor %ax, %ax
+ mov %ax, %es
ret
+
+str_read_error: .asciz "Read error while reading track: "
+
+abort_read:
+ mov $str_read_error, %esi
+ call putstr
+ mov cur_track, %eax
+ call print_num
+ mov $10, %al
+ call putchar
+
+ cli
+0: hlt
+ 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:
+ pushal
+ call ser_putchar
+
+ cmp $10, %al
+ jnz 0f
+ call video_newline
+ jmp 1f
+
+0: push %eax
+ mov cursor_y, %eax
+ mov $80, %ecx
+ mul %ecx
+ add cursor_x, %eax
+ mov %eax, %ebx
+ pop %eax
+
+ mov $0xb8000, %edx
+
+ # this looks retarded. in nasm: [ebx * 2 + edx]
+ mov %al, (%edx, %ebx, 2)
+ movb $7, 1(%edx, %ebx, 2)
+ incl cursor_x
+ cmpl $80, cursor_x
+ jnz 1f
+ call video_newline
+
+1: popal
+ ret
+
+ # expects string pointer in esi
+putstr:
+ mov (%esi), %al
+ cmp $0, %al
+ jz 0f
+ call putchar
+ inc %esi
+ jmp putstr
+0: ret
+
+ # expects number in eax
+print_num:
+ # save registers
+ pushal
+
+ mov $numbuf + 16, %esi
+ movb $0, (%esi)
+ mov $10, %ebx
+convloop:
+ xor %edx, %edx
+ div %ebx
+ add $48, %dl
+ dec %esi
+ mov %dl, (%esi)
+ cmp $0, %eax
+ jnz convloop
+
+ call putstr
+
+ # restore regs
+ popal
+ ret
+
+
+video_newline:
+ movl $0, cursor_x
+ incl cursor_y
+ cmpl $25, cursor_y
+ jnz 0f
+ call scrollup
+ decl cursor_y
+0: ret
+
+scrollup:
+ pushal
+ # move 80 * 24 lines from b80a0 -> b8000
+ mov $0xb8000, %edi
+ mov $0xb80a0, %esi
+ mov $960, %ecx
+ addr32 rep movsl
+ # clear last line (b8f00)
+ mov $0xb8f00, %edi
+ xor %eax, %eax
+ mov $40, %ecx
+ addr32 rep stosl
+ popal
+ ret
+
+clearscr:
+ mov $0xb8000, %edi
+ xor %eax, %eax
+ mov $1000, %ecx
+ addr32 rep stosl
+ ret
+
+ .set UART_DATA, 0x3f8
+ .set UART_LSTAT, 0x3fd
+ .set LST_TREG_EMPTY, 0x20
+
+ser_putchar:
+ push %dx
+
+ cmp $10, %al
+ jnz 0f
+ push %ax
+ mov $13, %al
+ call ser_putchar
+ pop %ax
+
+0: mov %al, %ah
+ # wait until the transmit register is empty
+ mov $UART_LSTAT, %dx
+wait: in %dx, %al
+ and $LST_TREG_EMPTY, %al
+ jz wait
+ mov $UART_DATA, %dx
+ mov %ah, %al
+ out %al, %dx
+
+ pop %dx
+ ret
+
+
+
+ena20_msg: .asciz "A20 line enabled\n"
+
+enable_a20:
+ call test_a20
+ jnc a20done
+ call enable_a20_kbd
+ call test_a20
+ jnc a20done
+ call enable_a20_fast
+ call test_a20
+ jnc a20done
+ # keep trying ... we can't do anything useful without A20 anyway
+ jmp enable_a20
+a20done:
+ mov $ena20_msg, %esi
+ call putstr
+ ret
+
+ # CF = 1 if A20 test fails (not enabled)
+test_a20:
+ mov $0x07c000, %ebx
+ mov $0x17c000, %edx
+ movl $0xbaadf00d, (%ebx)
+ movl $0xaabbcc42, (%edx)
+ subl $0xbaadf00d, (%ebx)
+ ret
+
+ # enable A20 line through port 0x92 (fast A20)
+enable_a20_fast:
+ mov $ena20_fast_msg, %esi
+ call putstr
+
+ in $0x92, %al
+ or $2, %al
+ out %al, $0x92
+ ret
+
+ena20_fast_msg: .asciz "Attempting fast A20 enable\n"
+
+
+ # enable A20 line through the keyboard controller
+ .set KBC_DATA_PORT, 0x60
+ .set KBC_CMD_PORT, 0x64
+ .set KBC_STATUS_PORT, 0x64
+ .set KBC_CMD_RD_OUTPORT, 0xd0
+ .set KBC_CMD_WR_OUTPORT, 0xd1
+
+ .set KBC_STAT_OUT_RDY, 0x01
+ .set KBC_STAT_IN_FULL, 0x02
+
+enable_a20_kbd:
+ mov $ena20_kbd_msg, %esi
+ call putstr
+
+ call kbc_wait_write
+ mov $KBC_CMD_WR_OUTPORT, %al
+ out %al, $KBC_CMD_PORT
+ call kbc_wait_write
+ mov $0xdf, %al
+ out %al, $KBC_DATA_PORT
+ ret
+
+ena20_kbd_msg: .asciz "Attempting KBD A20 enable\n"
+
+ # wait until the keyboard controller is ready to accept another byte
+kbc_wait_write:
+ in $KBC_STATUS_PORT, %al
+ and $KBC_STAT_IN_FULL, %al
+ jnz kbc_wait_write
+ ret
+
+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.
+
+ .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
+
+ # drop back to unreal mode to set video mode
+ .global set_mode13h
+set_mode13h:
+ pushal
+ cli
+ # save protected mode IDTR and replace it with the real mode vectors
+ sidt (saved_idtr)
+ lidt (rmidt)
+
+ # 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
+
+ # switch video mode by calling the video bios
+ mov $0x13, %ax
+ int $0x10
+
+ # 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
+
+ # restore 32bit interrupt descriptor table
+ lidt (saved_idtr)
+ sti
+ popal
+ ret
+
+
+ # buffer used by the track loader ... to load tracks.
+ .align 16
+buffer:
projects / bootcensus / blobdiff