1 /*
2 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License as
6 * published by the Free Software Foundation; either version 2 of the
7 * License, or any later version.
8 *
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
17 */
18
19 FILE_LICENCE ( GPL2_OR_LATER );
20
21 /**
22 * @file
23 *
24 * x86 bootsector image format
25 *
26 */
27
28 #include <errno.h>
29 #include <realmode.h>
30 #include <biosint.h>
31 #include <bootsector.h>
32
33 /** Vector for storing original INT 18 handler
34 *
35 * We do not chain to this vector, so there is no need to place it in
36 * .text16.
37 */
38 static struct segoff int18_vector;
39
40 /** Vector for storing original INT 19 handler
41 *
42 * We do not chain to this vector, so there is no need to place it in
43 * .text16.
44 */
45 static struct segoff int19_vector;
46
47 /** Restart point for INT 18 or 19 */
48 extern void bootsector_exec_fail ( void );
49
50 /**
51 * Jump to preloaded bootsector
52 *
53 * @v segment Real-mode segment
54 * @v offset Real-mode offset
55 * @v drive Drive number to pass to boot sector
56 * @ret rc Return status code
57 */
call_bootsector(unsigned int segment,unsigned int offset,unsigned int drive)58 int call_bootsector ( unsigned int segment, unsigned int offset,
59 unsigned int drive ) {
60 int discard_b, discard_D, discard_d;
61
62 DBG ( "Booting from boot sector at %04x:%04x\n", segment, offset );
63
64 /* Hook INTs 18 and 19 to capture failure paths */
65 hook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
66 &int18_vector );
67 hook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
68 &int19_vector );
69
70 /* Boot the loaded sector
71 *
72 * We assume that the boot sector may completely destroy our
73 * real-mode stack, so we preserve everything we need in
74 * static storage.
75 */
76 __asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
77 "popw %%cs:saved_retaddr\n\t"
78 /* Save stack pointer */
79 "movw %%ss, %%ax\n\t"
80 "movw %%ax, %%cs:saved_ss\n\t"
81 "movw %%sp, %%cs:saved_sp\n\t"
82 /* Jump to boot sector */
83 "pushw %%bx\n\t"
84 "pushw %%di\n\t"
85 "sti\n\t"
86 "lret\n\t"
87 /* Preserved variables */
88 "\nsaved_ss: .word 0\n\t"
89 "\nsaved_sp: .word 0\n\t"
90 "\nsaved_retaddr: .word 0\n\t"
91 /* Boot failure return point */
92 "\nbootsector_exec_fail:\n\t"
93 /* Restore stack pointer */
94 "movw %%cs:saved_ss, %%ax\n\t"
95 "movw %%ax, %%ss\n\t"
96 "movw %%cs:saved_sp, %%sp\n\t"
97 /* Return via saved address */
98 "jmp *%%cs:saved_retaddr\n\t" )
99 : "=b" ( discard_b ), "=D" ( discard_D ),
100 "=d" ( discard_d )
101 : "b" ( segment ), "D" ( offset ),
102 "d" ( drive )
103 : "eax", "ecx", "esi", "ebp" );
104
105 DBG ( "Booted disk returned via INT 18 or 19\n" );
106
107 /* Unhook INTs 18 and 19 */
108 unhook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
109 &int18_vector );
110 unhook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
111 &int19_vector );
112
113 return -ECANCELED;
114 }
115