+++ /dev/null
-#ident "$Id$"
-/* ----------------------------------------------------------------------- *
- *
- * Copyright 2003 H. Peter Anvin - All Rights Reserved
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, Inc., 53 Temple Place Ste 330,
- * Bostom MA 02111-1307, USA; either version 2 of the License, or
- * (at your option) any later version; incorporated herein by reference.
- *
- * ----------------------------------------------------------------------- */
-
-/*
- * chain.c
- *
- * Chainload a hard disk (currently rather braindead.)
- *
- * Usage: chain hd<disk#> [<partition>]
- * chain fd<disk#>
- *
- * ... e.g. "chain hd0 1" will boot the first partition on the first hard disk.
- *
- * Only partitions 1-4 supported at this time; 0 = boot MBR (default.)
- */
-
-#include <com32.h>
-#define NULL ((void *)0)
-
-int printf(const char *, ...);
-int puts(const char *);
-unsigned int skip_atou(char * const *);
-
-#define memset(x,y,z) __builtin_memset(x,y,z)
-#define memcpy(x,y,z) __builtin_memcpy(x,y,z)
-
-#define SECTOR 512 /* bytes/sector */
-
-static inline void error(const char *msg)
-{
- puts(msg);
-}
-
-static inline int isspace(char x)
-{
- return (x == ' ') || (x >= '\b' && x <= '\r');
-}
-
-/*
- * Call int 13h, but with retry on failure. Especially floppies need this.
- */
-int int13_retry(const com32sys_t *inreg, com32sys_t *outreg)
-{
- int retry = 6; /* Number of retries */
- com32sys_t tmpregs;
-
- if ( !outreg ) outreg = &tmpregs;
-
- while ( retry ) {
- __com32.cs_intcall(0x13, inreg, outreg);
- if ( (outreg->eflags.l & 1) == 0 )
- return 0; /* CF=0, OK */
- }
-
- return -1; /* Error */
-}
-
-/*
- * Query disk parameters and EBIOS availability for a particular disk.
- */
-struct diskinfo {
- int disk;
- int head;
- int sect;
- int ebios;
-} disk_info;
-
-int get_disk_params(int disk)
-{
- com32sys_t getparm, parm, getebios, ebios;
-
- memset(&getparm, 0, sizeof getparm);
- memset(&getebios, 0, sizeof getebios);
- memset(&disk_info, 0, sizeof disk_info);
-
- disk_info.disk = disk;
-
- if ( disk & 0x80 ) {
- /* Get disk parameters -- hard drives only */
-
- getparm.eax.b[1] = 0x08;
- getparm.edx.b[0] = disk;
- if ( int13_retry(&getparm, &parm) )
- return -1;
-
- disk_info.head = parm.edx.b[1]+1;
- disk_info.sect = parm.ecx.b[0] & 0x3f;
-
- /* Get EBIOS support */
-
- getebios.eax.w[0] = 0x4100;
- getebios.edx.b[0] = disk;
- getebios.ebx.w[0] = 0x55aa;
- getebios.eflags.b[0] = 0x3; /* CF set */
- if ( !int13_retry(&getebios, &ebios) ) {
- if ( ebios.ebx.w[0] == 0xaa55 &&
- (ebios.ecx.b[0] & 1) )
- disk_info.ebios = 1;
- }
- }
-
- return 0;
-}
-
-/*
- * Get a disk block; buf is REQUIRED TO BE IN LOW MEMORY.
- */
-struct ebios_dapa {
- uint16_t len;
- uint16_t count;
- uint16_t off;
- uint16_t seg;
- uint64_t lba;
-} *dapa;
-
-int read_sector(void *buf, unsigned int lba)
-{
- com32sys_t inreg;
-
- memset(&inreg, 0, sizeof inreg);
-
- if ( disk_info.ebios ) {
- dapa->len = sizeof(*dapa);
- dapa->count = 1; /* 1 sector */
- dapa->off = OFFS(buf);
- dapa->seg = SEG(buf);
- dapa->lba = lba;
-
- inreg.esi.w[0] = OFFS(dapa);
- inreg.ds = SEG(dapa);
- inreg.edx.b[0] = disk_info.disk;
- inreg.eax.b[1] = 0x42; /* Extended read */
- } else {
- unsigned int c, h, s, t;
-
- s = (lba % disk_info.sect) + 1;
- t = lba / disk_info.sect; /* Track = head*cyl */
- h = t % disk_info.head;
- c = t / disk_info.head;
-
- if ( s > 63 || h > 256 || c > 1023 )
- return -1;
-
- inreg.eax.w[0] = 0x0201; /* Read one sector */
- inreg.ecx.b[1] = c & 0xff;
- inreg.ecx.b[0] = s + (c >> 6);
- inreg.edx.b[1] = h;
- inreg.edx.b[0] = disk_info.disk;
- inreg.ebx.w[0] = OFFS(buf);
- inreg.es = SEG(buf);
- }
-
- return int13_retry(&inreg, NULL);
-}
-
-/* A DOS partition table entry */
-struct part_entry {
- uint8_t active_flag; /* 0x80 if "active" */
- uint8_t start_head;
- uint8_t start_sect;
- uint8_t start_cyl;
- uint8_t ostype;
- uint8_t end_head;
- uint8_t end_sect;
- uint8_t end_cyl;
- uint32_t start_lba;
- uint32_t length;
-} __attribute__((packed));
-
-
-/* Search for a logical partition. Logical partitions are actually implemented
- as recursive partition tables; theoretically they're supposed to form a linked
- list, but other structures have been seen.
-
- To make things extra confusing: data partition offsets are relative to where
- the data partition record is stored, whereas extended partition offsets
- are relative to the beginning of the extended partition all the way back
- at the MBR... but still not absolute! */
-
-int nextpart; /* Number of the next logical partition */
-
-struct part_entry *find_logical_partition(int whichpart, char *table, struct part_entry *self, struct part_entry *root)
-{
- struct part_entry *ptab = (struct part_entry *)(table + 0x1be);
- struct part_entry *found;
- int i;
-
- if ( *(uint16_t *)(ptab + 0x1fe) != 0xaa55 )
- return NULL; /* Signature missing */
-
- /* We are assumed to already having enumerated all the data partitions
- in this table if this is the MBR. For MBR, self == NULL. */
-
- if ( self ) {
- /* Scan the data partitions. */
-
- for ( i = 0 ; i < 4 ; i++ ) {
- if ( ptab[i].ostype == 0x00 || ptab[i].ostype == 0x05 ||
- ptab[i].ostype == 0x0f || ptab[i].ostype == 0x85 )
- continue; /* Skip empty or extended partitions */
-
- if ( !ptab[i].length )
- continue;
-
- /* Adjust the offset to account for the extended partition itself */
- ptab[i].start_lba += self->start_lba;
-
- /* Sanity check entry: must not extend outside the extended partition.
- This is necessary since some OSes put crap in some entries. */
- if ( ptab[i].start_lba + ptab[i].length <= self->start_lba ||
- ptab[i].start_lba >= self->start_lba + self->length )
- continue;
-
- /* OK, it's a data partition. Is it the one we're looking for? */
- if ( nextpart++ == whichpart )
- return &ptab[i];
- }
- }
-
- /* Scan the extended partitions. */
- for ( i = 0 ; i < 4 ; i++ ) {
- if ( ptab[i].ostype != 0x05 &&
- ptab[i].ostype != 0x0f && ptab[i].ostype != 0x85 )
- continue; /* Skip empty or data partitions */
-
- if ( !ptab[i].length )
- continue;
-
- /* Adjust the offset to account for the extended partition itself */
- if ( root )
- ptab[i].start_lba += root->start_lba;
-
- /* Sanity check entry: must not extend outside the extended partition.
- This is necessary since some OSes put crap in some entries. */
- if ( root )
- if ( ptab[i].start_lba + ptab[i].length <= root->start_lba ||
- ptab[i].start_lba >= root->start_lba + root->length )
- continue;
-
- /* Process this partition */
- if ( read_sector(table+SECTOR, ptab[i].start_lba) )
- continue; /* Read error, must be invalid */
-
- if ( (found = find_logical_partition(whichpart, table+SECTOR, &ptab[i],
- root ? root : &ptab[i])) )
- return found;
- }
-
- /* If we get here, there ain't nothing... */
- return NULL;
-}
-
-
-int __start(void)
-{
- char *mbr, *boot_sector = NULL;
- struct part_entry *partinfo;
- char *cmdline = __com32.cs_cmdline;
- int hd, drive, whichpart;
- static com32sys_t inreg; /* In bss, so zeroed automatically */
-
- /* Parse command line */
- while ( isspace(*cmdline) )
- cmdline++;
-
- hd = 0;
- if ( (cmdline[0] == 'h' || cmdline[0] == 'f') &&
- cmdline[1] == 'd' ) {
- hd = cmdline[0] == 'h';
- cmdline += 2;
- }
- drive = (hd ? 0x80 : 0) | skip_atou(&cmdline);
- whichpart = 0; /* Default */
-
- if ( isspace(*cmdline) ) {
- while ( isspace(*cmdline) )
- cmdline++;
-
- whichpart = skip_atou(&cmdline);
- }
-
- if ( !(drive & 0x80) && whichpart != 0 ) {
- error("Partitions not supported on floppy drives\n");
- goto bail;
- }
-
- /* Divvy up the bounce buffer. To keep things sector-
- aligned, give the EBIOS DAPA the first sector, then
- the MBR next, and the rest is used for the partition-
- chasing stack. */
- dapa = (struct ebios_dapa *)__com32.cs_bounce;
- mbr = (char *)__com32.cs_bounce + SECTOR;
-
- /* Get the MBR */
- if ( get_disk_params(drive) ) {
- error("Cannot get disk parameters\n");
- goto bail;
- }
-
- if ( read_sector(mbr, 0) ) {
- error("Cannot read MBR\n");
- goto bail;
- }
-
- if ( whichpart == 0 ) {
- /* Boot the MBR */
- partinfo = NULL;
- boot_sector = mbr;
- } else if ( whichpart <= 4 ) {
- /* Boot a primary partition */
- partinfo = &((struct part_entry *)(mbr + 0x1be))[whichpart-1];
- if ( partinfo->ostype == 0 ) {
- error("Invalid primary partition\n");
- goto bail;
- }
- } else {
- /* Boot a logical partition */
-
- nextpart = 5;
- partinfo = find_logical_partition(whichpart, mbr, NULL, NULL);
-
- if ( !partinfo || partinfo->ostype == 0 ) {
- error("Requested logical partition not found\n");
- goto bail;
- }
- }
-
- /* Do the actual chainloading */
- if ( partinfo ) {
- /* Actually read the boot sector */
- /* Pick the first buffer that isn't already in use */
- boot_sector = (char *)(((unsigned long)partinfo + 511) & ~511);
- if ( read_sector(boot_sector, partinfo->start_lba) ) {
- error("Cannot read boot sector\n");
- goto bail;
- }
-
- /* 0x7BE is the canonical place for the first partition entry. */
- inreg.esi.w[0] = 0x7be;
- memcpy((char *)0x7be, partinfo, sizeof(*partinfo));
- }
- inreg.eax.w[0] = 0x000d; /* Clean up and chain boot */
- inreg.edx.w[0] = 0; /* Should be 3 for "keeppxe" */
- inreg.edi.l = (uint32_t)boot_sector;
- inreg.ecx.l = SECTOR; /* One sector */
- inreg.ebx.b[0] = drive; /* DL = drive no */
-
- __com32.cs_intcall(0x22, &inreg, NULL);
-
- /* If we get here, badness happened */
- error("Chainboot failed!\n");
-
-bail:
- return 255;
-}
-
-
-
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