142 lines
4.3 KiB
C
142 lines
4.3 KiB
C
/*
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* Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*
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* You can also choose to distribute this program under the terms of
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* the Unmodified Binary Distribution Licence (as given in the file
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* COPYING.UBDL), provided that you have satisfied its requirements.
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*/
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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/**
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* @file
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*
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* x86 bootsector image format
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*
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*/
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#include <errno.h>
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#include <realmode.h>
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#include <biosint.h>
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#include <bootsector.h>
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#include <ipxe/console.h>
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/** Vector for storing original INT 18 handler
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*
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* We do not chain to this vector, so there is no need to place it in
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* .text16.
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*/
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static struct segoff int18_vector;
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/** Vector for storing original INT 19 handler
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*
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* We do not chain to this vector, so there is no need to place it in
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* .text16.
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*/
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static struct segoff int19_vector;
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/** Restart point for INT 18 or 19 */
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extern void bootsector_exec_fail ( void );
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/**
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* Jump to preloaded bootsector
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*
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* @v segment Real-mode segment
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* @v offset Real-mode offset
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* @v drive Drive number to pass to boot sector
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* @ret rc Return status code
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*/
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int call_bootsector ( unsigned int segment, unsigned int offset,
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unsigned int drive ) {
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int discard_b, discard_D, discard_d;
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/* Reset console, since boot sector will probably use it */
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console_reset();
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DBG ( "Booting from boot sector at %04x:%04x\n", segment, offset );
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/* Hook INTs 18 and 19 to capture failure paths */
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hook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
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&int18_vector );
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hook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
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&int19_vector );
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/* Boot the loaded sector
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*
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* We assume that the boot sector may completely destroy our
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* real-mode stack, so we preserve everything we need in
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* static storage.
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*/
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__asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
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"popw %%cs:saved_retaddr\n\t"
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/* Save stack pointer */
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"movw %%ss, %%ax\n\t"
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"movw %%ax, %%cs:saved_ss\n\t"
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"movw %%sp, %%cs:saved_sp\n\t"
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/* Save frame pointer (gcc bug) */
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"movl %%ebp, %%cs:saved_ebp\n\t"
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/* Prepare jump to boot sector */
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"pushw %%bx\n\t"
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"pushw %%di\n\t"
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/* Clear all registers */
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"xorl %%eax, %%eax\n\t"
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"xorl %%ebx, %%ebx\n\t"
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"xorl %%ecx, %%ecx\n\t"
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/* %edx contains drive number */
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"xorl %%esi, %%esi\n\t"
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"xorl %%edi, %%edi\n\t"
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"xorl %%ebp, %%ebp\n\t"
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"movw %%ax, %%ds\n\t"
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"movw %%ax, %%es\n\t"
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"movw %%ax, %%fs\n\t"
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"movw %%ax, %%gs\n\t"
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/* Jump to boot sector */
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"sti\n\t"
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"lret\n\t"
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/* Preserved variables */
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"\nsaved_ebp: .long 0\n\t"
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"\nsaved_ss: .word 0\n\t"
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"\nsaved_sp: .word 0\n\t"
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"\nsaved_retaddr: .word 0\n\t"
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/* Boot failure return point */
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"\nbootsector_exec_fail:\n\t"
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/* Restore frame pointer (gcc bug) */
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"movl %%cs:saved_ebp, %%ebp\n\t"
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/* Restore stack pointer */
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"movw %%cs:saved_ss, %%ax\n\t"
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"movw %%ax, %%ss\n\t"
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"movw %%cs:saved_sp, %%sp\n\t"
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/* Return via saved address */
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"jmp *%%cs:saved_retaddr\n\t" )
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: "=b" ( discard_b ), "=D" ( discard_D ),
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"=d" ( discard_d )
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: "b" ( segment ), "D" ( offset ),
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"d" ( drive )
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: "eax", "ecx", "esi" );
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DBG ( "Booted disk returned via INT 18 or 19\n" );
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/* Unhook INTs 18 and 19 */
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unhook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
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&int18_vector );
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unhook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
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&int19_vector );
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return -ECANCELED;
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}
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