d0f7acf9eb
An x86-64 operating system built from xv6, now largely rewritten: SMP, a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF rasteriser, and a Linux-numbered syscall ABI. No history before this point -- the tree was never under version control. This commit exists so the rename that follows has something to undo to.
129 lines
3.3 KiB
ArmAsm
129 lines
3.3 KiB
ArmAsm
# Stage 2 — loaded by stage1 at 0x7E00, still in 16-bit real mode. Does the
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# VBE mode setup, A20 line, and real->protected mode switch that used to
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# live directly in the boot sector, then hands off to stage2main() (C) to
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# draw a splash and load the actual kernel. Not sector-size-constrained —
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# only bounded by STAGE2_SECTORS in bootasm.S / the Makefile.
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#include "../include/asm.h"
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#include "../include/memlayout.h"
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#include "../include/mmu.h"
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.code16
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.global stage2start
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stage2start:
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# Segments are already zeroed by stage1; %sp is inherited too.
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movw $bootmsg, %si
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call print16
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# VBE Setup. Mode info block goes at 0x30000, not 0x9000 — stage2 itself
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# is loaded starting at 0x7E00 and, with the boot-menu/progress-bar code,
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# is now big enough to reach 0x9000, so writing the VBE block there would
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# clobber stage2's own tail end. 0x30000 is clear of stage2 (ends well
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# under 0xA000), the multiboot kernel-search buffer (0x10000-0x14000),
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# and the kernel's own load address (0x100000).
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movw $0x3000, %ax
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movw %ax, %es
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xorw %di, %di # ES:DI = 3000:0000 = flat 0x30000
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movw $0x0143, %cx
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movw $0x4F01, %ax
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int $0x10
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cmpw $0x004F, %ax
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jne e820
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movw $0x4143, %bx
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movw $0x4F02, %ax
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int $0x10
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# BIOS E820 memory map — the standard firmware interface every serious
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# loader (GRUB, Linux's own boot stub, the BSDs) uses to learn the real
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# RAM layout instead of guessing. Entry count goes to flat 0x30200,
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# 24-byte entries start at 0x30208 (both inside the 0x3000 segment the
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# VBE block already claimed; verbose flag sits at +0x100). Capped at 32
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# entries so a pathological BIOS can't run us past the buffer.
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e820:
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movw $0x3000, %ax
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movw %ax, %es
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xorl %ebx, %ebx # continuation cookie, 0 = first call
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movw $0x208, %di
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xorl %ebp, %ebp # entry count
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e820loop:
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movl $0xE820, %eax
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movl $0x534D4150, %edx # 'SMAP'
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movl $24, %ecx
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int $0x15
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jc e820done # carry = end of map (or unsupported BIOS)
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cmpl $0x534D4150, %eax
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jne e820done
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addw $24, %di
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incl %ebp
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cmpl $32, %ebp
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jae e820done
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testl %ebx, %ebx
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jnz e820loop
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e820done:
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movl %ebp, %es:(0x200)
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xorw %ax, %ax
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movw %ax, %es
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seta20.1:
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inb $0x64, %al
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testb $0x2, %al
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jnz seta20.1
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movb $0xd1, %al
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outb %al, $0x64
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seta20.2:
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inb $0x64, %al
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testb $0x2, %al
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jnz seta20.2
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movb $0xdf, %al
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outb %al, $0x60
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lgdt gdtdesc
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movl %cr0, %eax
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orl $CR0_PE, %eax
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movl %eax, %cr0
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ljmp $(SEG_KCODE<<3), $start32
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# Print null-terminated string at DS:SI via BIOS teletype (real mode only).
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# Clobbers AX, BX, SI.
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print16:
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.Lp16loop:
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lodsb
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testb %al, %al
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jz .Lp16done
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movb $0x0E, %ah
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movw $0x0007, %bx
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int $0x10
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jmp .Lp16loop
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.Lp16done:
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ret
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bootmsg:
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.asciz "Schunix booting...\r\n"
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.code32
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start32:
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movw $(SEG_KDATA<<3), %ax
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %ss
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xorw %ax, %ax
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movw %ax, %fs
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movw %ax, %gs
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movl $0x7c00, %esp
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call stage2main
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spin:
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jmp spin
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.p2align 2
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gdt:
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SEG_NULLASM
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SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff)
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SEG_ASM(STA_W, 0x0, 0xffffffff)
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gdtdesc:
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.word (gdtdesc - gdt - 1)
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.long gdt
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