biossums.c

   1 /* biossums.c  --- written by Eike W. for the Bochs BIOS */
   2 /* adapted for the LGPL'd VGABIOS by vruppert */
   3
   4 /*  This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU Lesser General Public
   6  *  License as published by the Free Software Foundation; either
   7  *  version 2 of the License, or (at your option) any later version.
   8  *
   9  *  This library is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  *  Lesser General Public License for more details.
  13  *
  14  *  You should have received a copy of the GNU Lesser General Public
  15  *  License along with this library; if not, write to the Free Software
  16  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
  17  */
  18 #include <stdlib.h>
  19 #include <stdio.h>
  20
  21 typedef unsigned char byte;
  22
  23 void check( int value, char* message );
  24
  25 #define LEN_BIOS_DATA 0x8000
  26 #define MAX_OFFSET    (LEN_BIOS_DATA - 1)
  27
  28
  29 #define BIOS_OFFSET 0x7FFF
  30
  31 long chksum_bios_get_offset( byte* data, long offset );
  32 byte chksum_bios_calc_value( byte* data, long offset );
  33 byte chksum_bios_get_value(  byte* data, long offset );
  34 void chksum_bios_set_value(  byte* data, long offset, byte value );
  35
  36
  37 #define PMID_LEN        20
  38 #define PMID_CHKSUM     19
  39
  40 long chksum_pmid_get_offset( byte* data, long offset );
  41 byte chksum_pmid_calc_value( byte* data, long offset );
  42 byte chksum_pmid_get_value(  byte* data, long offset );
  43 void chksum_pmid_set_value(  byte* data, long offset, byte value );
  44
  45
  46 byte bios_data[LEN_BIOS_DATA];
  47
  48
  49 int main( int argc, char* argv[] ) {
  50
  51   FILE* stream;
  52   long  offset, tmp_offset;
  53   byte  cur_val = 0, new_val = 0;
  54   int   hits;
  55
  56
  57   if( argc != 2 ) {
  58     printf( "Error. Need a file-name as an argument.\n" );
  59     exit( EXIT_FAILURE );
  60   }
  61
  62   if(( stream = fopen( argv[1], "rb" )) == NULL ) {
  63     printf( "Error opening %s for reading.\n", argv[1] );
  64     exit( EXIT_FAILURE );
  65   }
  66   if( fread( bios_data, 1, LEN_BIOS_DATA, stream ) >= LEN_BIOS_DATA ) {
  67     printf( "Error reading max. 32767 Bytes from %s.\n", argv[1] );
  68     fclose( stream );
  69     exit( EXIT_FAILURE );
  70   }
  71   fclose( stream );
  72
  73   hits   = 0;
  74   offset = 0L;
  75   while( (tmp_offset = chksum_pmid_get_offset( bios_data, offset )) != -1L ) {
  76     offset  = tmp_offset;
  77     cur_val = chksum_pmid_get_value(  bios_data, offset );
  78     new_val = chksum_pmid_calc_value( bios_data, offset );
  79     printf( "\nPMID entry at: 0x%4lX\n", offset  );
  80     printf( "Current checksum:     0x%02X\n",   cur_val );
  81     printf( "Calculated checksum:  0x%02X  ",   new_val );
  82     hits++;
  83   }
  84   if( hits == 1 && cur_val != new_val ) {
  85     printf( "Setting checksum." );
  86     chksum_pmid_set_value( bios_data, offset, new_val );
  87   }
  88   if( hits >= 2 ) {
  89     printf( "Multiple PMID entries! No checksum set." );
  90   }
  91   if( hits ) {
  92     printf( "\n" );
  93   }
  94
  95
  96   offset  = 0L;
  97   offset  = chksum_bios_get_offset( bios_data, offset );
  98   cur_val = chksum_bios_get_value(  bios_data, offset );
  99   new_val = chksum_bios_calc_value( bios_data, offset );
 100   printf( "\nBios checksum at:   0x%4lX\n", offset  );
 101   printf( "Current checksum:     0x%02X\n",   cur_val );
 102   printf( "Calculated checksum:  0x%02X  ",   new_val );
 103   if( cur_val != new_val ) {
 104     printf( "Setting checksum." );
 105     chksum_bios_set_value( bios_data, offset, new_val );
 106   }
 107   printf( "\n" );
 108
 109
 110   if(( stream = fopen( argv[1], "wb" )) == NULL ) {
 111     printf( "Error opening %s for writing.\n", argv[1] );
 112     exit( EXIT_FAILURE );
 113   }
 114   if( fwrite( bios_data, 1, LEN_BIOS_DATA, stream ) < LEN_BIOS_DATA ) {
 115     printf( "Error writing 32KBytes to %s.\n", argv[1] );
 116     fclose( stream );
 117     exit( EXIT_FAILURE );
 118   }
 119   fclose( stream );
 120
 121   return( EXIT_SUCCESS );
 122 }
 123
 124
 125 void check( int okay, char* message ) {
 126
 127   if( !okay ) {
 128     printf( "\n\nError. %s.\n", message );
 129     exit( EXIT_FAILURE );
 130   }
 131 }
 132
 133
 134 long chksum_bios_get_offset( byte* data, long offset ) {
 135
 136   return( BIOS_OFFSET );
 137 }
 138
 139
 140 byte chksum_bios_calc_value( byte* data, long offset ) {
 141
 142   int   i;
 143   byte  sum;
 144
 145   sum = 0;
 146   for( i = 0; i < MAX_OFFSET; i++ ) {
 147     sum = sum + *( data + i );
 148   }
 149   sum = -sum;          /* iso ensures -s + s == 0 on unsigned types */
 150   return( sum );
 151 }
 152
 153
 154 byte chksum_bios_get_value( byte* data, long offset ) {
 155
 156   return( *( data + BIOS_OFFSET ) );
 157 }
 158
 159
 160 void chksum_bios_set_value( byte* data, long offset, byte value ) {
 161
 162   *( data + BIOS_OFFSET ) = value;
 163 }
 164
 165
 166 byte chksum_pmid_calc_value( byte* data, long offset ) {
 167
 168   int           i;
 169   int           len;
 170   byte sum;
 171
 172   len = PMID_LEN;
 173   check( offset + len <= MAX_OFFSET, "PMID entry length out of bounds" );
 174   sum = 0;
 175   for( i = 0; i < len; i++ ) {
 176     if( i != PMID_CHKSUM ) {
 177       sum = sum + *( data + offset + i );
 178     }
 179   }
 180   sum = -sum;
 181   return( sum );
 182 }
 183
 184
 185 long chksum_pmid_get_offset( byte* data, long offset ) {
 186
 187   long result = -1L;
 188
 189   while( offset + PMID_LEN < MAX_OFFSET ) {
 190     offset = offset + 1;
 191     if( *( data + offset + 0 ) == 'P' && \
 192         *( data + offset + 1 ) == 'M' && \
 193         *( data + offset + 2 ) == 'I' && \
 194         *( data + offset + 3 ) == 'D' ) {
 195       result = offset;
 196       break;
 197     }
 198   }
 199   return( result );
 200 }
 201
 202
 203 byte chksum_pmid_get_value( byte* data, long offset ) {
 204
 205   check( offset + PMID_CHKSUM <= MAX_OFFSET, "PMID checksum out of bounds" );
 206   return(  *( data + offset + PMID_CHKSUM ) );
 207 }
 208
 209
 210 void chksum_pmid_set_value( byte* data, long offset, byte value ) {
 211
 212   check( offset + PMID_CHKSUM <= MAX_OFFSET, "PMID checksum out of bounds" );
 213   *( data + offset + PMID_CHKSUM ) = value;
 214 }