libcom32-ize the chain loader; add LICENCE file

3 files changed, 394 insertions, 1 deletions

diff --git a/com32/LICENCE b/com32/LICENCE
new file mode 100644
index 00000000..feb8a12c
--- /dev/null
+++ b/com32/LICENCE
@@ -0,0 +1,31 @@
+libcom32 and libutil are licensed under the MIT license:
+
+## -----------------------------------------------------------------------
+##   
+##   Copyright 2004 H. Peter Anvin - All Rights Reserved
+##
+##   Permission is hereby granted, free of charge, to any person
+##   obtaining a copy of this software and associated documentation
+##   files (the "Software"), to deal in the Software without
+##   restriction, including without limitation the rights to use,
+##   copy, modify, merge, publish, distribute, sublicense, and/or
+##   sell copies of the Software, and to permit persons to whom
+##   the Software is furnished to do so, subject to the following
+##   conditions:
+##   
+##   The above copyright notice and this permission notice shall
+##   be included in all copies or substantial portions of the Software.
+##   
+##   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+##   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+##   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+##   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+##   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+##   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+##   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+##   OTHER DEALINGS IN THE SOFTWARE.
+##
+## -----------------------------------------------------------------------
+
+The files in the modules directory are mostly under the GNU GPL (see
+the file COPYING in the directory above.)
diff --git a/com32/modules/Makefile b/com32/modules/Makefile
index 7f24159d..971dc95c 100644
--- a/com32/modules/Makefile
+++ b/com32/modules/Makefile
@@ -39,7 +39,10 @@ LNXLIBS	   = ../libutil/libutil_lnx.a
 
 .SUFFIXES: .lss .c .o .elf .c32 .lnx
 
-all: hello.c32 fancyhello.c32 fancyhello.lnx keytest.c32 keytest.lnx
+all: hello.c32 \
+	fancyhello.c32 fancyhello.lnx \
+	keytest.c32 keytest.lnx \
+	chain.c32
 
 .PRECIOUS: %.o
 %.o: %.S
diff --git a/com32/modules/chain.c b/com32/modules/chain.c
new file mode 100644
index 00000000..9b7f15b0
--- /dev/null
+++ b/com32/modules/chain.c
@@ -0,0 +1,359 @@
+#ident "$Id$"
+/* ----------------------------------------------------------------------- *
+ *   
+ *   Copyright 2003-2004 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>
+#include <stdlib.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <string.h>
+
+#define SECTOR 512		/* bytes/sector */
+
+static inline void error(const char *msg)
+{
+  puts(msg);
+}
+
+/*
+ * 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 ) {
+    __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 main(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) | strtoul(cmdline, &cmdline, 0);
+  whichpart = 0;		/* Default */
+
+  if ( isspace(*cmdline) ) {
+    while ( isspace(*cmdline) )
+      cmdline++;
+
+    whichpart = strtoul(cmdline, NULL, 0);
+  }
+
+  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 */
+
+  __intcall(0x22, &inreg, NULL);
+
+  /* If we get here, badness happened */
+  error("Chainboot failed!\n");
+
+bail:
+  return 255;
+}
+
+
+