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
  20 FILE_LICENCE ( GPL2_OR_LATER );
  21
  22 /**
  23  * @file
  24  *
  25  * x86 bootsector image format
  26  *
  27  */
  28
  29 #include <errno.h>
  30 #include <realmode.h>
  31 #include <biosint.h>
  32 #include <bootsector.h>
  33 #include <ipxe/console.h>
  34
  35 /** Vector for storing original INT 18 handler
  36  *
  37  * We do not chain to this vector, so there is no need to place it in
  38  * .text16.
  39  */
  40 static struct segoff int18_vector;
  41
  42 /** Vector for storing original INT 19 handler
  43  *
  44  * We do not chain to this vector, so there is no need to place it in
  45  * .text16.
  46  */
  47 static struct segoff int19_vector;
  48
  49 /** Restart point for INT 18 or 19 */
  50 extern void bootsector_exec_fail ( void );
  51
  52 /**
  53  * Jump to preloaded bootsector
  54  *
  55  * @v segment           Real-mode segment
  56  * @v offset            Real-mode offset
  57  * @v drive             Drive number to pass to boot sector
  58  * @ret rc              Return status code
  59  */
  60 int call_bootsector ( unsigned int segment, unsigned int offset,
  61                       unsigned int drive ) {
  62         int discard_b, discard_D, discard_d;
  63
  64         /* Reset console, since boot sector will probably use it */
  65         console_reset();
  66
  67         DBG ( "Booting from boot sector at %04x:%04x\n", segment, offset );
  68
  69         /* Hook INTs 18 and 19 to capture failure paths */
  70         hook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
  71                               &int18_vector );
  72         hook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
  73                               &int19_vector );
  74
  75         /* Boot the loaded sector
  76          *
  77          * We assume that the boot sector may completely destroy our
  78          * real-mode stack, so we preserve everything we need in
  79          * static storage.
  80          */
  81         __asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
  82                                            "popw %%cs:saved_retaddr\n\t"
  83                                            /* Save stack pointer */
  84                                            "movw %%ss, %%ax\n\t"
  85                                            "movw %%ax, %%cs:saved_ss\n\t"
  86                                            "movw %%sp, %%cs:saved_sp\n\t"
  87                                            /* Save frame pointer (gcc bug) */
  88                                            "movl %%ebp, %%cs:saved_ebp\n\t"
  89                                            /* Prepare jump to boot sector */
  90                                            "pushw %%bx\n\t"
  91                                            "pushw %%di\n\t"
  92                                            /* Clear all registers */
  93                                            "xorl %%eax, %%eax\n\t"
  94                                            "xorl %%ebx, %%ebx\n\t"
  95                                            "xorl %%ecx, %%ecx\n\t"
  96                                            /* %edx contains drive number */
  97                                            "xorl %%esi, %%esi\n\t"
  98                                            "xorl %%edi, %%edi\n\t"
  99                                            "xorl %%ebp, %%ebp\n\t"
 100                                            "movw %%ax, %%ds\n\t"
 101                                            "movw %%ax, %%es\n\t"
 102                                            "movw %%ax, %%fs\n\t"
 103                                            "movw %%ax, %%gs\n\t"
 104                                            /* Jump to boot sector */
 105                                            "sti\n\t"
 106                                            "lret\n\t"
 107                                            /* Preserved variables */
 108                                            "\nsaved_ebp: .long 0\n\t"
 109                                            "\nsaved_ss: .word 0\n\t"
 110                                            "\nsaved_sp: .word 0\n\t"
 111                                            "\nsaved_retaddr: .word 0\n\t"
 112                                            /* Boot failure return point */
 113                                            "\nbootsector_exec_fail:\n\t"
 114                                            /* Restore frame pointer (gcc bug) */
 115                                            "movl %%cs:saved_ebp, %%ebp\n\t"
 116                                            /* Restore stack pointer */
 117                                            "movw %%cs:saved_ss, %%ax\n\t"
 118                                            "movw %%ax, %%ss\n\t"
 119                                            "movw %%cs:saved_sp, %%sp\n\t"
 120                                            /* Return via saved address */
 121                                            "jmp *%%cs:saved_retaddr\n\t" )
 122                                : "=b" ( discard_b ), "=D" ( discard_D ),
 123                                  "=d" ( discard_d )
 124                                : "b" ( segment ), "D" ( offset ),
 125                                  "d" ( drive )
 126                                : "eax", "ecx", "esi" );
 127
 128         DBG ( "Booted disk returned via INT 18 or 19\n" );
 129
 130         /* Unhook INTs 18 and 19 */
 131         unhook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
 132                                 &int18_vector );
 133         unhook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
 134                                 &int19_vector );
 135
 136         return -ECANCELED;
 137 }