qemu/roms/ipxe/src/arch/i386/image/bootsector.c

   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., 51 Franklin Street, Fifth Floor, Boston, MA
  17  * 02110-1301, USA.
  18  *
  19  * You can also choose to distribute this program under the terms of
  20  * the Unmodified Binary Distribution Licence (as given in the file
  21  * COPYING.UBDL), provided that you have satisfied its requirements.
  22  */
  23
  24 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  25
  26 /**
  27  * @file
  28  *
  29  * x86 bootsector image format
  30  *
  31  */
  32
  33 #include <errno.h>
  34 #include <realmode.h>
  35 #include <biosint.h>
  36 #include <bootsector.h>
  37 #include <ipxe/console.h>
  38
  39 /** Vector for storing original INT 18 handler
  40  *
  41  * We do not chain to this vector, so there is no need to place it in
  42  * .text16.
  43  */
  44 static struct segoff int18_vector;
  45
  46 /** Vector for storing original INT 19 handler
  47  *
  48  * We do not chain to this vector, so there is no need to place it in
  49  * .text16.
  50  */
  51 static struct segoff int19_vector;
  52
  53 /** Restart point for INT 18 or 19 */
  54 extern void bootsector_exec_fail ( void );
  55
  56 /**
  57  * Jump to preloaded bootsector
  58  *
  59  * @v segment           Real-mode segment
  60  * @v offset            Real-mode offset
  61  * @v drive             Drive number to pass to boot sector
  62  * @ret rc              Return status code
  63  */
  64 int call_bootsector ( unsigned int segment, unsigned int offset,
  65                       unsigned int drive ) {
  66         int discard_b, discard_D, discard_d;
  67
  68         /* Reset console, since boot sector will probably use it */
  69         console_reset();
  70
  71         DBG ( "Booting from boot sector at %04x:%04x\n", segment, offset );
  72
  73         /* Hook INTs 18 and 19 to capture failure paths */
  74         hook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
  75                               &int18_vector );
  76         hook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
  77                               &int19_vector );
  78
  79         /* Boot the loaded sector
  80          *
  81          * We assume that the boot sector may completely destroy our
  82          * real-mode stack, so we preserve everything we need in
  83          * static storage.
  84          */
  85         __asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
  86                                            "popw %%cs:saved_retaddr\n\t"
  87                                            /* Save stack pointer */
  88                                            "movw %%ss, %%ax\n\t"
  89                                            "movw %%ax, %%cs:saved_ss\n\t"
  90                                            "movw %%sp, %%cs:saved_sp\n\t"
  91                                            /* Save frame pointer (gcc bug) */
  92                                            "movl %%ebp, %%cs:saved_ebp\n\t"
  93                                            /* Prepare jump to boot sector */
  94                                            "pushw %%bx\n\t"
  95                                            "pushw %%di\n\t"
  96                                            /* Clear all registers */
  97                                            "xorl %%eax, %%eax\n\t"
  98                                            "xorl %%ebx, %%ebx\n\t"
  99                                            "xorl %%ecx, %%ecx\n\t"
 100                                            /* %edx contains drive number */
 101                                            "xorl %%esi, %%esi\n\t"
 102                                            "xorl %%edi, %%edi\n\t"
 103                                            "xorl %%ebp, %%ebp\n\t"
 104                                            "movw %%ax, %%ds\n\t"
 105                                            "movw %%ax, %%es\n\t"
 106                                            "movw %%ax, %%fs\n\t"
 107                                            "movw %%ax, %%gs\n\t"
 108                                            /* Jump to boot sector */
 109                                            "sti\n\t"
 110                                            "lret\n\t"
 111                                            /* Preserved variables */
 112                                            "\nsaved_ebp: .long 0\n\t"
 113                                            "\nsaved_ss: .word 0\n\t"
 114                                            "\nsaved_sp: .word 0\n\t"
 115                                            "\nsaved_retaddr: .word 0\n\t"
 116                                            /* Boot failure return point */
 117                                            "\nbootsector_exec_fail:\n\t"
 118                                            /* Restore frame pointer (gcc bug) */
 119                                            "movl %%cs:saved_ebp, %%ebp\n\t"
 120                                            /* Restore stack pointer */
 121                                            "movw %%cs:saved_ss, %%ax\n\t"
 122                                            "movw %%ax, %%ss\n\t"
 123                                            "movw %%cs:saved_sp, %%sp\n\t"
 124                                            /* Return via saved address */
 125                                            "jmp *%%cs:saved_retaddr\n\t" )
 126                                : "=b" ( discard_b ), "=D" ( discard_D ),
 127                                  "=d" ( discard_d )
 128                                : "b" ( segment ), "D" ( offset ),
 129                                  "d" ( drive )
 130                                : "eax", "ecx", "esi" );
 131
 132         DBG ( "Booted disk returned via INT 18 or 19\n" );
 133
 134         /* Unhook INTs 18 and 19 */
 135         unhook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
 136                                 &int18_vector );
 137         unhook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
 138                                 &int19_vector );
 139
 140         return -ECANCELED;
 141 }