com32/modules/chain.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2003-2005 H. Peter Anvin - All Rights Reserved
   4  *
   5  *   This program is free software; you can redistribute it and/or modify
   6  *   it under the terms of the GNU General Public License as published by
   7  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   8  *   Boston MA 02111-1307, USA; either version 2 of the License, or
   9  *   (at your option) any later version; incorporated herein by reference.
  10  *
  11  * ----------------------------------------------------------------------- */
  12
  13 /*
  14  * chain.c
  15  *
  16  * Chainload a hard disk (currently rather braindead.)
  17  *
  18  * Usage: chain hd<disk#> [<partition>]
  19  *        chain fd<disk#>
  20  *
  21  * ... e.g. "chain hd0 1" will boot the first partition on the first hard disk.
  22  *
  23  * Partitions 1-4 are primary, 5+ logical, 0 = boot MBR (default.)
  24  */
  25
  26 #include <com32.h>
  27 #include <stdlib.h>
  28 #include <stdio.h>
  29 #include <ctype.h>
  30 #include <string.h>
  31 #include <console.h>
  32
  33 #define SECTOR 512              /* bytes/sector */
  34
  35 static inline void error(const char *msg)
  36 {
  37   fputs(msg, stderr);
  38 }
  39
  40 /*
  41  * Call int 13h, but with retry on failure.  Especially floppies need this.
  42  */
  43 int int13_retry(const com32sys_t *inreg, com32sys_t *outreg)
  44 {
  45   int retry = 6;                /* Number of retries */
  46   com32sys_t tmpregs;
  47
  48   if ( !outreg ) outreg = &tmpregs;
  49
  50   while ( retry-- ) {
  51     __intcall(0x13, inreg, outreg);
  52     if ( !(outreg->eflags.l & EFLAGS_CF) )
  53       return 0;                 /* CF=0, OK */
  54   }
  55
  56   return -1;                    /* Error */
  57 }
  58
  59 /*
  60  * Query disk parameters and EBIOS availability for a particular disk.
  61  */
  62 struct diskinfo {
  63   int disk;
  64   int ebios;                    /* EBIOS supported on this disk */
  65   int cbios;                    /* CHS geometry is valid */
  66   int head;
  67   int sect;
  68 } disk_info;
  69
  70 int get_disk_params(int disk)
  71 {
  72   static com32sys_t getparm, parm, getebios, ebios;
  73
  74   disk_info.disk = disk;
  75
  76   /* Get EBIOS support */
  77   getebios.eax.w[0] = 0x4100;
  78   getebios.ebx.w[0] = 0x55aa;
  79   getebios.edx.b[0] = disk;
  80   getebios.eflags.b[0] = 0x3;   /* CF set */
  81
  82   __intcall(0x13, &getebios, &ebios);
  83
  84   if ( !(ebios.eflags.l & EFLAGS_CF) &&
  85        ebios.ebx.w[0] == 0xaa55 &&
  86        (ebios.ecx.b[0] & 1) ) {
  87     disk_info.ebios = 1;
  88   }
  89
  90   /* Get disk parameters -- really only useful for
  91      hard disks, but if we have a partitioned floppy
  92      it's actually our best chance... */
  93   getparm.eax.b[1] = 0x08;
  94   getparm.edx.b[0] = disk;
  95
  96   __intcall(0x13, &getparm, &parm);
  97
  98   if ( parm.eflags.l & EFLAGS_CF )
  99     return disk_info.ebios ? 0 : -1;
 100
 101   disk_info.head = parm.edx.b[1]+1;
 102   disk_info.sect = parm.ecx.b[0] & 0x3f;
 103   if ( disk_info.sect == 0 ) {
 104     disk_info.sect = 1;
 105   } else {
 106     disk_info.cbios = 1;        /* Valid geometry */
 107   }
 108
 109   return 0;
 110 }
 111
 112 /*
 113  * Get a disk block; buf is REQUIRED TO BE IN LOW MEMORY.
 114  */
 115 struct ebios_dapa {
 116   uint16_t len;
 117   uint16_t count;
 118   uint16_t off;
 119   uint16_t seg;
 120   uint64_t lba;
 121 } *dapa;
 122
 123 int read_sector(void *buf, unsigned int lba)
 124 {
 125   com32sys_t inreg;
 126
 127   memset(&inreg, 0, sizeof inreg);
 128
 129   if ( disk_info.ebios ) {
 130     dapa->len = sizeof(*dapa);
 131     dapa->count = 1;            /* 1 sector */
 132     dapa->off = OFFS(buf);
 133     dapa->seg = SEG(buf);
 134     dapa->lba = lba;
 135
 136     inreg.esi.w[0] = OFFS(dapa);
 137     inreg.ds       = SEG(dapa);
 138     inreg.edx.b[0] = disk_info.disk;
 139     inreg.eax.b[1] = 0x42;      /* Extended read */
 140   } else {
 141     unsigned int c, h, s, t;
 142
 143     if ( !disk_info.cbios ) {
 144       /* We failed to get the geometry */
 145
 146       if ( lba )
 147         return -1;              /* Can only read MBR */
 148
 149       s = 1;  h = 0;  c = 0;
 150     } else {
 151       s = (lba % disk_info.sect) + 1;
 152       t = lba / disk_info.sect; /* Track = head*cyl */
 153       h = t % disk_info.head;
 154       c = t / disk_info.head;
 155     }
 156
 157     if ( s > 63 || h > 256 || c > 1023 )
 158       return -1;
 159
 160     inreg.eax.w[0] = 0x0201;    /* Read one sector */
 161     inreg.ecx.b[1] = c & 0xff;
 162     inreg.ecx.b[0] = s + (c >> 6);
 163     inreg.edx.b[1] = h;
 164     inreg.edx.b[0] = disk_info.disk;
 165     inreg.ebx.w[0] = OFFS(buf);
 166     inreg.es       = SEG(buf);
 167   }
 168
 169   return int13_retry(&inreg, NULL);
 170 }
 171
 172 /* A DOS partition table entry */
 173 struct part_entry {
 174   uint8_t active_flag;          /* 0x80 if "active" */
 175   uint8_t start_head;
 176   uint8_t start_sect;
 177   uint8_t start_cyl;
 178   uint8_t ostype;
 179   uint8_t end_head;
 180   uint8_t end_sect;
 181   uint8_t end_cyl;
 182   uint32_t start_lba;
 183   uint32_t length;
 184 } __attribute__((packed));
 185
 186
 187 /* Search for a logical partition.  Logical partitions are actually implemented
 188    as recursive partition tables; theoretically they're supposed to form a linked
 189    list, but other structures have been seen.
 190
 191    To make things extra confusing: data partition offsets are relative to where
 192    the data partition record is stored, whereas extended partition offsets
 193    are relative to the beginning of the extended partition all the way back
 194    at the MBR... but still not absolute! */
 195
 196 int nextpart;                   /* Number of the next logical partition */
 197
 198 struct part_entry *find_logical_partition(int whichpart, char *table, struct part_entry *self, struct part_entry *root)
 199 {
 200   struct part_entry *ptab = (struct part_entry *)(table + 0x1be);
 201   struct part_entry *found;
 202   int i;
 203
 204   if ( *(uint16_t *)(ptab + 0x1fe) != 0xaa55 )
 205     return NULL;                /* Signature missing */
 206
 207   /* We are assumed to already having enumerated all the data partitions
 208      in this table if this is the MBR.  For MBR, self == NULL. */
 209
 210   if ( self ) {
 211     /* Scan the data partitions. */
 212
 213     for ( i = 0 ; i < 4 ; i++ ) {
 214       if ( ptab[i].ostype == 0x00 || ptab[i].ostype == 0x05 ||
 215            ptab[i].ostype == 0x0f || ptab[i].ostype == 0x85 )
 216         continue;               /* Skip empty or extended partitions */
 217
 218       if ( !ptab[i].length )
 219         continue;
 220
 221       /* Adjust the offset to account for the extended partition itself */
 222       ptab[i].start_lba += self->start_lba;
 223
 224       /* Sanity check entry: must not extend outside the extended partition.
 225          This is necessary since some OSes put crap in some entries. */
 226       if ( ptab[i].start_lba + ptab[i].length <= self->start_lba ||
 227            ptab[i].start_lba >= self->start_lba + self->length )
 228         continue;
 229
 230       /* OK, it's a data partition.  Is it the one we're looking for? */
 231       if ( nextpart++ == whichpart )
 232         return &ptab[i];
 233     }
 234   }
 235
 236   /* Scan the extended partitions. */
 237   for ( i = 0 ; i < 4 ; i++ ) {
 238     if ( ptab[i].ostype != 0x05 &&
 239          ptab[i].ostype != 0x0f && ptab[i].ostype != 0x85 )
 240       continue;         /* Skip empty or data partitions */
 241
 242     if ( !ptab[i].length )
 243       continue;
 244
 245     /* Adjust the offset to account for the extended partition itself */
 246     if ( root )
 247       ptab[i].start_lba += root->start_lba;
 248
 249     /* Sanity check entry: must not extend outside the extended partition.
 250        This is necessary since some OSes put crap in some entries. */
 251     if ( root )
 252       if ( ptab[i].start_lba + ptab[i].length <= root->start_lba ||
 253            ptab[i].start_lba >= root->start_lba + root->length )
 254         continue;
 255
 256     /* Process this partition */
 257     if ( read_sector(table+SECTOR, ptab[i].start_lba) )
 258       continue;                 /* Read error, must be invalid */
 259
 260     if ( (found = find_logical_partition(whichpart, table+SECTOR, &ptab[i],
 261                                          root ? root : &ptab[i])) )
 262       return found;
 263   }
 264
 265   /* If we get here, there ain't nothing... */
 266   return NULL;
 267 }
 268
 269
 270 int main(int argc, char *argv[])
 271 {
 272   char *mbr, *boot_sector = NULL;
 273   struct part_entry *partinfo;
 274   char *drivename, *partition;
 275   int hd, drive, whichpart;
 276   static com32sys_t inreg;      /* In bss, so zeroed automatically */
 277
 278   openconsole(&dev_null_r, &dev_stdcon_w);
 279
 280   if ( argc < 2 ) {
 281     error("Usage: chain.c32 (hd|fd)# [partition]\n");
 282     goto bail;
 283   }
 284
 285   drivename = argv[1];
 286   partition = argv[2];          /* Possibly null */
 287
 288   hd = 0;
 289   if ( (drivename[0] == 'h' || drivename[0] == 'f') &&
 290        drivename[1] == 'd' ) {
 291     hd = drivename[0] == 'h';
 292     drivename += 2;
 293   }
 294   drive = (hd ? 0x80 : 0) | strtoul(drivename, NULL, 0);
 295   whichpart = 0;                /* Default */
 296
 297   if ( partition )
 298     whichpart = strtoul(partition, NULL, 0);
 299
 300   if ( !(drive & 0x80) && whichpart ) {
 301     error("Warning: Partitions of floppy devices may not work\n");
 302   }
 303
 304   /* Divvy up the bounce buffer.  To keep things sector-
 305      aligned, give the EBIOS DAPA the first sector, then
 306      the MBR next, and the rest is used for the partition-
 307      chasing stack. */
 308   dapa = (struct ebios_dapa *)__com32.cs_bounce;
 309   mbr  = (char *)__com32.cs_bounce + SECTOR;
 310
 311   /* Get the disk geometry (not needed for MBR) */
 312   if ( get_disk_params(drive) && whichpart ) {
 313     error("Cannot get disk parameters\n");
 314     goto bail;
 315   }
 316
 317   /* Get MBR */
 318   if ( read_sector(mbr, 0) ) {
 319     error("Cannot read Master Boot Record\n");
 320     goto bail;
 321   }
 322
 323   if ( whichpart == 0 ) {
 324     /* Boot the MBR */
 325     partinfo = NULL;
 326     boot_sector = mbr;
 327   } else if ( whichpart <= 4 ) {
 328     /* Boot a primary partition */
 329     partinfo = &((struct part_entry *)(mbr + 0x1be))[whichpart-1];
 330     if ( partinfo->ostype == 0 ) {
 331       error("Invalid primary partition\n");
 332       goto bail;
 333     }
 334   } else {
 335     /* Boot a logical partition */
 336
 337     nextpart = 5;
 338     partinfo = find_logical_partition(whichpart, mbr, NULL, NULL);
 339
 340     if ( !partinfo || partinfo->ostype == 0 ) {
 341       error("Requested logical partition not found\n");
 342       goto bail;
 343     }
 344   }
 345
 346   /* Do the actual chainloading */
 347   if ( partinfo ) {
 348     /* Actually read the boot sector */
 349     /* Pick the first buffer that isn't already in use */
 350     boot_sector = (char *)(((unsigned long)partinfo + 511) & ~511);
 351     if ( read_sector(boot_sector, partinfo->start_lba) ) {
 352       error("Cannot read boot sector\n");
 353       goto bail;
 354     }
 355
 356     /* 0x7BE is the canonical place for the first partition entry. */
 357     inreg.esi.w[0] = 0x7be;
 358     memcpy((char *)0x7be, partinfo, sizeof(*partinfo));
 359   }
 360
 361   fputs("Booting...\n", stdout);
 362
 363   inreg.eax.w[0] = 0x000d;      /* Clean up and chain boot */
 364   inreg.edx.w[0] = 0;           /* Should be 3 for "keeppxe" */
 365   inreg.edi.l    = (uint32_t)boot_sector;
 366   inreg.ecx.l    = SECTOR;      /* One sector */
 367   inreg.ebx.b[0] = drive;       /* DL = drive no */
 368
 369   __intcall(0x22, &inreg, NULL);
 370
 371   /* If we get here, badness happened */
 372   error("Chainboot failed!\n");
 373
 374 bail:
 375   return 255;
 376 }