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/*
* Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
*
* 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 2 of the
* License, or 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, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
FILE_LICENCE ( GPL2_OR_LATER );
/**
* @file
*
* x86 bootsector image format
*
*/
#include <errno.h>
#include <realmode.h>
#include <biosint.h>
#include <bootsector.h>
/** Vector for storing original INT 18 handler
*
* We do not chain to this vector, so there is no need to place it in
* .text16.
*/
static struct segoff int18_vector;
/** Vector for storing original INT 19 handler
*
* We do not chain to this vector, so there is no need to place it in
* .text16.
*/
static struct segoff int19_vector;
/** Restart point for INT 18 or 19 */
extern void bootsector_exec_fail ( void );
/**
* Jump to preloaded bootsector
*
* @v segment Real-mode segment
* @v offset Real-mode offset
* @v drive Drive number to pass to boot sector
* @ret rc Return status code
*/
int call_bootsector ( unsigned int segment, unsigned int offset,
unsigned int drive ) {
int discard_b, discard_D, discard_d;
DBG ( "Booting from boot sector at %04x:%04x\n", segment, offset );
/* Hook INTs 18 and 19 to capture failure paths */
hook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
&int18_vector );
hook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
&int19_vector );
/* Boot the loaded sector
*
* We assume that the boot sector may completely destroy our
* real-mode stack, so we preserve everything we need in
* static storage.
*/
__asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
"popw %%cs:saved_retaddr\n\t"
/* Save stack pointer */
"movw %%ss, %%ax\n\t"
"movw %%ax, %%cs:saved_ss\n\t"
"movw %%sp, %%cs:saved_sp\n\t"
/* Jump to boot sector */
"pushw %%bx\n\t"
"pushw %%di\n\t"
"sti\n\t"
"lret\n\t"
/* Preserved variables */
"\nsaved_ss: .word 0\n\t"
"\nsaved_sp: .word 0\n\t"
"\nsaved_retaddr: .word 0\n\t"
/* Boot failure return point */
"\nbootsector_exec_fail:\n\t"
/* Restore stack pointer */
"movw %%cs:saved_ss, %%ax\n\t"
"movw %%ax, %%ss\n\t"
"movw %%cs:saved_sp, %%sp\n\t"
/* Return via saved address */
"jmp *%%cs:saved_retaddr\n\t" )
: "=b" ( discard_b ), "=D" ( discard_D ),
"=d" ( discard_d )
: "b" ( segment ), "D" ( offset ),
"d" ( drive )
: "eax", "ecx", "esi", "ebp" );
DBG ( "Booted disk returned via INT 18 or 19\n" );
/* Unhook INTs 18 and 19 */
unhook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
&int18_vector );
unhook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
&int19_vector );
return -ECANCELED;
}
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