copied from src/system/boot/platform/bios_ia32/shell.S
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@18917 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Marcus Overhagen
@@ -0,0 +1,376 @@
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/*
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* Copyright 2004-2005, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
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* Distributed under the terms of the MIT License.
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*/
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/** This file contains the boot floppy and BFS boot block entry points for
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* the stage 2 boot loader.
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* The floppy entry point is at offset 0. It's loaded at 0x07c0:0x000. It
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* will load the rest of the loader to 0x1000:0x0200 and execute it.
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* The BFS boot block will load the whole stage 2 loader to 0x1000:0x0000
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* and will then jump to 0x1000:0x0200 as its entry point.
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* This code will then switch to protected mode and will directly call
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* the entry function of the embedded ELF part of the loader.
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*/
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#define GLOBAL(x) .globl x ; x
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// this saves us some trouble with relocation (I didn't manage GAS to
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// create 32 bit references to labels)
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#define FAILURE_STRING 0x1d0
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#define DOT_STRING 0x1fc
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#define DRIVE_RETRIES 3
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// when the drive reading fails for some reason, it will
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// retry this many times until it will report a failure
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.text
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.code16
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/** This is the entry point when we were written directly to a floppy disk */
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jmp floppy_start
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sNumSectors:
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// this location will contain the length of the boot loader as
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// written by the "makeflop" command in 512 byte blocks
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// 0x180 is the allowed maximum, as the zipped TAR with the
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// kernel and the boot module might start at offset 192 kB
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.word 0x0180
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floppy_start:
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cli
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cld
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// set up the stack to 0x0000:0x9000
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xor %ax, %ax
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mov %ax, %ss
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mov $0x9000, %sp
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push $0x07c0
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pop %ds
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push $0x1000
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pop %es
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// load the rest of the boot loader to 0x1000:0x0200
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.code32 // we need to create a 32-bit relocation entry for the linker...
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.byte 0x67
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movw sNumSectors - 0x10000, %di
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// the loader symbols are located at offset 0x10000
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.code16
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xor %dh, %dh // head 0, don't change BIOS boot device
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mov $0x2, %cx // sector 2
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mov $0x200, %bx // to 0x1000:0x0200
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call load_sectors
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// ToDo: this seems to be problematic, at least under Bochs (reboot will fail)
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#if 0
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or %dl, %dl // if it's a floppy, turn off its motor
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jnz start_loader
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call disable_floppy_motor
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#endif
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start_loader:
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// indicate that we were booted from CD/floppy/whatever
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.code32
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.byte 0x67
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movb $1, gBootedFromImage - 0x7c00
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// %ds is 0x7c0 right now, but the symbol were loaded
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// to offset 0x10000
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.code16
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// set our environment and jump to the standard BFS boot block entry point
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xor %dx, %dx // boot device ID and partition offset to 0
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xor %eax, %eax
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ljmp $0x1000, $0x0200
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/** Loads %di sectors from floppy disk, starting at head %dh, sector %cx.
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* The data is loaded to %es:%bx. On exit, %es:%bx will point immediately
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* behind the loaded data, so that you can continue to read in data.
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* %ax, %cx, %dx, %bp, %di and %si will be clobbered.
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*/
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load_sectors:
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// first, get information about the drive as we intend to read whole tracks
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push %bx
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push %cx
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push %dx
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push %di
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push %es
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movb $8, %ah // get drive parameters - changes a lot of registers
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int $0x13
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pop %es
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pop %di
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// ToDo: store the number of heads somewhere (it's in %dh)
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pop %dx
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and $63, %cx // mask out max. sector number (bit 0-5)
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mov %cx, %si // and remember it
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pop %cx
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pop %bx
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load_track:
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mov %di, %ax // limit the sector count to track boundaries
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add %cl, %al
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dec %ax
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cmp %si, %ax
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jbe matches_track_boundary
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mov %si, %ax
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matches_track_boundary:
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inc %ax // take the current sector offset into account
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sub %cl, %al
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// make sure we don't cross a 64kB address boundary or else the read will fail
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// (this small piece of knowledge took me some time to accept :))
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shl $9, %ax
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mov %ax, %bp
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add %bx, %bp
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jnc respects_boundary
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xor %ax, %ax // only read up to the 64kB boundary
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sub %bx, %ax
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respects_boundary:
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shr $9, %ax
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mov DRIVE_RETRIES, %bp
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try_to_read:
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pusha
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movb $2, %ah // load sectors from drive
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int $0x13
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jnc read_succeeded
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xor %ax, %ax
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int $0x13 // reset drive
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popa
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dec %bp
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jz load_failed // if already retried often enough, bail out
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jmp try_to_read
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read_succeeded:
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mov $DOT_STRING, %si
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call print_string
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popa
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xor %ah, %ah
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add %ax, %cx // next sector start
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sub %ax, %di // update sectors left to be read
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shl $9, %ax // get byte offset
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add %ax, %bx // update target address
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jnz check_sector_start
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mov %es, %ax // overflow to the next 64kB, %bx is already zero
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add $0x1000, %ax
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mov %ax, %es
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check_sector_start:
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mov %si, %ax // compare the sectors, not the cylinders
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cmp %al, %cl
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jbe continue_reading
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sub %si, %cx
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inc %dh // next head
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cmp $1, %dh
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// ToDo: check max. number of heads!
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jbe check_sector_start
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xor %dh, %dh // next cylinder
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inc %ch
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jmp check_sector_start
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continue_reading:
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or %di, %di
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jnz load_track
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ret
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load_failed:
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mov $FAILURE_STRING, %si
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call print_string
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xor %ax, %ax
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int $0x16 // wait for key
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int $0x19 // and reboot
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disable_floppy_motor:
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xor %al, %al
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mov $0x3f2, %dx
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out %al, %dx
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ret
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print_string:
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movb $0x0e, %ah
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xor %bx, %bx
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print_char:
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lodsb
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orb %al, %al // are there still characters left?
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jz no_more_chars
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int $0x10
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jmp print_char
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no_more_chars:
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ret
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floppy_end:
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.org FAILURE_STRING
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.string " Loading failed! Press key to reboot.\r\n"
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.org DOT_STRING
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.string "."
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.org 0x01fe
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.word 0xaa55
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// this bumps the "start" label to offset 0x0200 as
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// expected by the BFS boot loader, and also marks
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// this block as valid boot block for the BIOS
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//--------------------------------------------------------------
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/** This is the entry point of the stage2 bootloader when it has
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* been loaded from the stage1 loader from a BFS disk.
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*/
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bfs_start:
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cld // set the data, and extra segment to our code start
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pushw $0x1000
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pop %ds
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push %ds
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pop %es
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.code32 // save knowledge from the BFS boot block for later use
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.byte 0x67
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movb %dl, gBootDriveID - 0x10000
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.byte 0x67
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.byte 0x66
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movl %eax, gBootPartitionOffset - 0x10000
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.code16
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xor %ax, %ax // set up stack at 0x0000:0x9000
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mov %ax, %ss
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mov $0x9000, %sp
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cli // no interrupts please
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call enable_a20 // enable a20 gate
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.code32 // This forces a 32 bit relocation entry
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.byte 0x66 // that allows linking with others
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.byte 0x67
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lgdt gdt_descriptor - 0x10000
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// load global descriptor table; we're still in real mode segment
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// 0x1000 so we have to manually correct the address
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.code16
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movl %cr0, %eax // set the PE bit of cr0 to switch to protected mode
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orb $0x1, %al
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movl %eax, %cr0
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.code32
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.byte 0x66
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ljmp $0x8, $_protected_code_segment
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_protected_code_segment:
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mov $0x10, %ax // load descriptor 2 in the data and stack segment selectors
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mov %ax, %ds
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mov %ax, %es
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mov %ax, %fs
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mov %ax, %gs
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mov %ax, %ss
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mov $0x10000, %ebp // setup new stack
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mov %ebp, %esp
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call _start
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//--------------------------------------------------------------
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/** Enables the a20 gate. It will first try to enable it through
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* the BIOS, and, if that fails, will use the old style AT mechanism
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* using the keyboard port.
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* ToDo: it no longer does this! Now, it just uses the "fast A20"
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* mechanism using port 0x92. This does work on all systems
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* I have access to.
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*/
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enable_a20:
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inb $0x92, %al
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testb $0x02, %al
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jnz _a20_out
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orb $0x02, %al
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andb $0xfe, %al
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outb %al, $0x92
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_a20_out:
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ret
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// ToDo: the code below didn't seem to work properly on all machines
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/* movw $0x2402, %ax // first, query the a20 status
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int $0x15
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jc _a20_old_method // if that fails, use the old AT method
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test $0x1, %al
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jnz _a20_done // Is a20 gate already enabled?
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movw $0x2401, %ax
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int $0x15
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jnc _a20_done
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_a20_old_method:
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call _a20_loop1 // empty the keyboard buffer
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jnz _a20_done
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movb $0xd1, %al
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outb %al, $0x64
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call _a20_loop1 // empty the keyboard buffer
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jnz _a20_done
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movb $0xdf, %al
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outb %al, $0x60
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_a20_loop1:
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movl $0x20000, %ecx
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_a20_loop2:
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inb $0x64, %al
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test $0x2, %al
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loopne _a20_loop2
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_a20_done:
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ret
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*/
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//--------------------------------------------------------------
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.org 896
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// since we don't need the above space when the boot loader is
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// running, it is used as a real mode scratch buffer (as our
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// boot loader spans over the whole real mode 0x1000 segment)
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/* global data table */
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gdt:
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// null descriptor
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.long 0
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.long 0
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// kernel code segment
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.long 0x0000ffff // base: 0, limit: 4 GB
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.long 0x00cf9e00 // type: 32 bit, exec-only conforming, privilege 0
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// kernel data and stack segment
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.long 0x0000ffff // base: 0, limit: 4 GB
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.long 0x00cf9200 // type: 32 bit, data read/write, privilege 0
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// real mode 16 bit code segment
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.long 0x0000ffff // base: 0x10000, limit: 64 kB
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.long 0x00009e01
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// real mode 16 bit data and stack segment
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.long 0x0000ffff // base: 0x10000, limit: 64 kB
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.long 0x00009201
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// real mode 16 bit stack segment
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.long 0x0000ffff // base: 0, limit: 64 kB
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.long 0x00009200
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gdt_descriptor:
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.word 0x2f // 6 entries in the GDT (8 bytes each)
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.long gdt
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GLOBAL(gBootedFromImage):
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.byte 0
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GLOBAL(gBootDriveID):
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.byte 0
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GLOBAL(gBootPartitionOffset):
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.long 0
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.org 1024
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