biossums.c

   1 /* biossums.c  --- written by Eike W. for the Bochs BIOS */
   2 /* adapted for the LGPL'd VGABIOS by vruppert */
   3
   4 #include <stdlib.h>
   5 #include <stdio.h>
   6
   7 typedef unsigned char byte;
   8
   9 void check( int value, char* message );
  10
  11 #define LEN_BIOS_DATA 0x8000
  12 #define MAX_OFFSET    (LEN_BIOS_DATA - 1)
  13
  14
  15 #define BIOS_OFFSET 0x7FFF
  16
  17 long chksum_bios_get_offset( byte* data, long offset );
  18 byte chksum_bios_calc_value( byte* data, long offset );
  19 byte chksum_bios_get_value(  byte* data, long offset );
  20 void chksum_bios_set_value(  byte* data, long offset, byte value );
  21
  22
  23 #define PMID_LEN        20
  24 #define PMID_CHKSUM     19
  25
  26 long chksum_pmid_get_offset( byte* data, long offset );
  27 byte chksum_pmid_calc_value( byte* data, long offset );
  28 byte chksum_pmid_get_value(  byte* data, long offset );
  29 void chksum_pmid_set_value(  byte* data, long offset, byte value );
  30
  31
  32 byte bios_data[LEN_BIOS_DATA];
  33
  34
  35 int main( int argc, char* argv[] ) {
  36
  37   FILE* stream;
  38   long  offset, tmp_offset;
  39   byte  cur_val = 0, new_val = 0;
  40   int   hits;
  41
  42
  43   if( argc != 2 ) {
  44     printf( "Error. Need a file-name as an argument.\n" );
  45     exit( EXIT_FAILURE );
  46   }
  47
  48   if(( stream = fopen( argv[1], "rb" )) == NULL ) {
  49     printf( "Error opening %s for reading.\n", argv[1] );
  50     exit( EXIT_FAILURE );
  51   }
  52   if( fread( bios_data, 1, LEN_BIOS_DATA, stream ) >= LEN_BIOS_DATA ) {
  53     printf( "Error reading max. 32767 Bytes from %s.\n", argv[1] );
  54     fclose( stream );
  55     exit( EXIT_FAILURE );
  56   }
  57   fclose( stream );
  58
  59   hits   = 0;
  60   offset = 0L;
  61   while( (tmp_offset = chksum_pmid_get_offset( bios_data, offset )) != -1L ) {
  62     offset  = tmp_offset;
  63     cur_val = chksum_pmid_get_value(  bios_data, offset );
  64     new_val = chksum_pmid_calc_value( bios_data, offset );
  65     printf( "\nPMID entry at: 0x%4lX\n", offset  );
  66     printf( "Current checksum:     0x%02X\n",   cur_val );
  67     printf( "Calculated checksum:  0x%02X  ",   new_val );
  68     hits++;
  69   }
  70   if( hits == 1 && cur_val != new_val ) {
  71     printf( "Setting checksum." );
  72     chksum_pmid_set_value( bios_data, offset, new_val );
  73   }
  74   if( hits >= 2 ) {
  75     printf( "Multiple PMID entries! No checksum set." );
  76   }
  77   if( hits ) {
  78     printf( "\n" );
  79   }
  80
  81
  82   offset  = 0L;
  83   offset  = chksum_bios_get_offset( bios_data, offset );
  84   cur_val = chksum_bios_get_value(  bios_data, offset );
  85   new_val = chksum_bios_calc_value( bios_data, offset );
  86   printf( "\nBios checksum at:   0x%4lX\n", offset  );
  87   printf( "Current checksum:     0x%02X\n",   cur_val );
  88   printf( "Calculated checksum:  0x%02X  ",   new_val );
  89   if( cur_val != new_val ) {
  90     printf( "Setting checksum." );
  91     chksum_bios_set_value( bios_data, offset, new_val );
  92   }
  93   printf( "\n" );
  94
  95
  96   if(( stream = fopen( argv[1], "wb" )) == NULL ) {
  97     printf( "Error opening %s for writing.\n", argv[1] );
  98     exit( EXIT_FAILURE );
  99   }
 100   if( fwrite( bios_data, 1, LEN_BIOS_DATA, stream ) < LEN_BIOS_DATA ) {
 101     printf( "Error writing 32KBytes to %s.\n", argv[1] );
 102     fclose( stream );
 103     exit( EXIT_FAILURE );
 104   }
 105   fclose( stream );
 106
 107   return( EXIT_SUCCESS );
 108 }
 109
 110
 111 void check( int okay, char* message ) {
 112
 113   if( !okay ) {
 114     printf( "\n\nError. %s.\n", message );
 115     exit( EXIT_FAILURE );
 116   }
 117 }
 118
 119
 120 long chksum_bios_get_offset( byte* data, long offset ) {
 121
 122   return( BIOS_OFFSET );
 123 }
 124
 125
 126 byte chksum_bios_calc_value( byte* data, long offset ) {
 127
 128   int   i;
 129   byte  sum;
 130
 131   sum = 0;
 132   for( i = 0; i < MAX_OFFSET; i++ ) {
 133     sum = sum + *( data + i );
 134   }
 135   sum = -sum;          /* iso ensures -s + s == 0 on unsigned types */
 136   return( sum );
 137 }
 138
 139
 140 byte chksum_bios_get_value( byte* data, long offset ) {
 141
 142   return( *( data + BIOS_OFFSET ) );
 143 }
 144
 145
 146 void chksum_bios_set_value( byte* data, long offset, byte value ) {
 147
 148   *( data + BIOS_OFFSET ) = value;
 149 }
 150
 151
 152 byte chksum_pmid_calc_value( byte* data, long offset ) {
 153
 154   int           i;
 155   int           len;
 156   byte sum;
 157
 158   len = PMID_LEN;
 159   check( offset + len <= MAX_OFFSET, "PMID entry length out of bounds" );
 160   sum = 0;
 161   for( i = 0; i < len; i++ ) {
 162     if( i != PMID_CHKSUM ) {
 163       sum = sum + *( data + offset + i );
 164     }
 165   }
 166   sum = -sum;
 167   return( sum );
 168 }
 169
 170
 171 long chksum_pmid_get_offset( byte* data, long offset ) {
 172
 173   long result = -1L;
 174
 175   while( offset + PMID_LEN < MAX_OFFSET ) {
 176     offset = offset + 1;
 177     if( *( data + offset + 0 ) == 'P' && \
 178         *( data + offset + 1 ) == 'M' && \
 179         *( data + offset + 2 ) == 'I' && \
 180         *( data + offset + 3 ) == 'D' ) {
 181       result = offset;
 182       break;
 183     }
 184   }
 185   return( result );
 186 }
 187
 188
 189 byte chksum_pmid_get_value( byte* data, long offset ) {
 190
 191   check( offset + PMID_CHKSUM <= MAX_OFFSET, "PMID checksum out of bounds" );
 192   return(  *( data + offset + PMID_CHKSUM ) );
 193 }
 194
 195
 196 void chksum_pmid_set_value( byte* data, long offset, byte value ) {
 197
 198   check( offset + PMID_CHKSUM <= MAX_OFFSET, "PMID checksum out of bounds" );
 199   *( data + offset + PMID_CHKSUM ) = value;
 200 }