boot.img: bootldr.bin $(bin)
cat bootldr.bin $(bin) >$@
-# bootldr.bin will contain only .boot and .boot2
+# bootldr.bin will contain .boot, .boot2, .bootend, and .lowtext
bootldr.bin: $(elf)
- objcopy -O binary -j '.boot*' $< $@
+ objcopy -O binary -j '.boot*' -j .lowtext $< $@
-# the main binary will contain every section *except* .boot and .boot2
+# the main binary will contain every section *except* those
$(bin): $(elf)
- objcopy -O binary -R '.boot*' $< $@
+ objcopy -O binary -R '.boot*' -R .lowtext $< $@
$(elf): $(obj)
$(LD) -o $@ $(obj) -Map link.map $(LDFLAGS)
objdump -d $< -j .boot -j .boot2 -m i8086 >$@
$(elf).disasm: $(elf)
- objdump -d $< -j .startup -j .text -m i386 >$@
+ objdump -d $< -j .startup -j .text -j .lowtext -m i386 >$@
$(elf).sym: $(elf)
objcopy --only-keep-debug $< $@
/* second stage boot loader */
.boot2 : {
* (.boot2);
+ * (.lowtext);
+ /* .bootend must stay last */
+ * (.bootend);
/* pad the boot loader to the next sector boundary */
. = ALIGN(512);
}
ret
+ # this part is placed at the very end of all low memory sections
+ .section .bootend,"ax"
.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
-saved_pic1_mask: .byte 0
-saved_pic2_mask: .byte 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)
-
- # save PIC masks
- pushl $0
- call get_pic_mask
- add $4, %esp
- mov %al, saved_pic1_mask
- pushl $1
- call get_pic_mask
- add $4, %esp
- mov %al, saved_pic2_mask
-
- # 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
-
- # 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
- popw %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
- # grab the flags and replace the carry bit from the saved flags
- pushfw
- popw %ax
- and $0xfffe, %ax
- or saved_flags, %ax
- pushw %ax
- mov saved_eax, %eax
- pushal
- mov saved_esp, %esp
-
- # restore 32bit interrupt descriptor table
- lidt (saved_idtr)
-
- # restore PIC configuration
- call init_pic
-
- # restore IRQ masks
- movzbl saved_pic1_mask, %eax
- push %eax
- pushl $0
- call set_pic_mask
- add $8, %esp
-
- movzbl saved_pic2_mask, %eax
- push %eax
- pushl $1
- call set_pic_mask
- add $8, %esp
-
- # keyboard voodoo: with some BIOS implementations, after returning from
- # int13, there's (I guess) leftover data in the keyboard port and we
- # can't receive any more keyboard interrupts afterwards. Reading from
- # the keyboard data port (60h) once, seems to resolve this. And it's
- # cheap enough, so why not... I give up.
- push %eax
- in $0x60, %al
- pop %eax
-
- sti
- popal
- pop %ebp
- ret
-
-
.align 4
.global boot_drive_number
boot_drive_number:
--- /dev/null
+# pcboot - bootable PC demo/game kernel
+# Copyright (C) 2018-2019 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/>.
+
+ .section .lowtext,"ax"
+
+ .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
+saved_pic1_mask: .byte 0
+saved_pic2_mask: .byte 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)
+
+ # save PIC masks
+ pushl $0
+ call get_pic_mask
+ add $4, %esp
+ mov %al, saved_pic1_mask
+ pushl $1
+ call get_pic_mask
+ add $4, %esp
+ mov %al, saved_pic2_mask
+
+ # 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
+
+ # 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
+ popw %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
+ # grab the flags and replace the carry bit from the saved flags
+ pushfw
+ popw %ax
+ and $0xfffe, %ax
+ or saved_flags, %ax
+ pushw %ax
+ mov saved_eax, %eax
+ pushal
+ mov saved_esp, %esp
+
+ # restore 32bit interrupt descriptor table
+ lidt (saved_idtr)
+
+ # restore PIC configuration
+ call init_pic
+
+ # restore IRQ masks
+ movzbl saved_pic1_mask, %eax
+ push %eax
+ pushl $0
+ call set_pic_mask
+ add $8, %esp
+
+ movzbl saved_pic2_mask, %eax
+ push %eax
+ pushl $1
+ call set_pic_mask
+ add $8, %esp
+
+ # keyboard voodoo: with some BIOS implementations, after returning from
+ # int13, there's (I guess) leftover data in the keyboard port and we
+ # can't receive any more keyboard interrupts afterwards. Reading from
+ # the keyboard data port (60h) once, seems to resolve this. And it's
+ # cheap enough, so why not... I give up.
+ push %eax
+ in $0x60, %al
+ pop %eax
+
+ sti
+ popal
+ pop %ebp
+ ret
projects / bootcensus / commitdiff