1 /* -----------------------------------------------------------------------
3 * Copyright 2007 H. Peter Anvin - All Rights Reserved
5 * Permission is hereby granted, free of charge, to any person
6 * obtaining a copy of this software and associated documentation
7 * files (the "Software"), to deal in the Software without
8 * restriction, including without limitation the rights to use,
9 * copy, modify, merge, publish, distribute, sublicense, and/or
10 * sell copies of the Software, and to permit persons to whom
11 * the Software is furnished to do so, subject to the following
14 * The above copyright notice and this permission notice shall
15 * be included in all copies or substantial portions of the Software.
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
18 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
19 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
20 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
21 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
22 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
23 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
24 * OTHER DEALINGS IN THE SOFTWARE.
26 * ----------------------------------------------------------------------- */
35 secpercyl = (stack-12)
39 /* gas/ld has issues with doing this as absolute addresses... */
40 .section ".bootsec", "a", @nobits
54 pushw %es /* es:di -> $PnP header */
56 pushw %dx /* dl -> drive number */
61 /* Copy down to 0:0x600 */
69 /* Check to see if we have EBIOS */
70 pushw %dx /* drive number */
80 shrw %cx /* Bit 0 = fixed disk subset */
83 /* We have EBIOS; patch in a jump to read_sector_ebios */
84 movw $0xeb+((read_sector_ebios-read_sector_cbios-2)<< 8), (read_sector_cbios)
89 /* Get (C)HS geometry */
92 andw $0x3f, %cx /* Sector count */
93 pushw %cx /* Save sectors on the stack */
95 pushw %ax /* High word of sectors/cylinder */
96 movb %dh, %al /* dh = number of heads */
97 incw %ax /* From 0-based to count */
98 mulw %cx /* Heads*sectors -> sectors per cylinder */
99 pushw %ax /* Save sectors/cylinder on the stack */
101 xorl %eax, %eax /* Base */
102 cdq /* Root (%edx <- 0) */
103 call scan_partition_table
105 /* If we get here, we have no OS */
109 * read_sector: read a single sector pointed to by %eax to 0x7c00.
110 * CF is set on error. All registers saved.
130 pushl %edx /* MSW of LBA */
131 pushl %eax /* LSW of LBA */
132 pushw %es /* Buffer segment */
133 pushw %bx /* Buffer offset */
134 pushw $1 /* Sector count */
135 pushw $16 /* Size of packet */
145 * read_partition_table:
146 * Read a partition table (pointed to by %eax), and copy
147 * the partition table into the ptab buffer.
148 * Clobbers %si, %di, and %cx, other registers preserved.
152 read_partition_table:
155 movw $bootsec+446, %si
163 * scan_partition_table:
164 * Scan a partition table currently loaded in the partition table
165 * area. Preserve all registers.
168 * %eax - base (location of this partition table)
169 * %edx - root (offset from MBR, or 0 for MBR)
171 * These get pushed into stack slots:
172 * 28(%bp) - %eax - base
173 * 20(%bp) - %edx - root
176 scan_partition_table:
180 /* Search for active partitions */
195 decw %ax /* Number of active partitions found */
199 /* No active partitions found, look for extended partitions */
200 popw %bx /* %bx <- ptab */
201 popw %cx /* %cx <- 4 */
204 cmpb $0x0f, %al /* 0x0f = Win9x extended */
206 andb $~0x80, %al /* 0x85 = Linux extended */
207 cmpb $0x05, %al /* 0x05 = MS-DOS extended */
210 /* It is an extended partition. Read the extended partition and
211 try to scan it. If the scan returns, re-load the current
212 partition table and resume scan. */
214 movl 8(%bx), %eax /* Partition table offset */
215 movl 20(%bp), %edx /* "Root" */
216 addl %edx, %eax /* Compute location of new ptab */
217 andl %edx, %edx /* Is this the MBR? */
219 movl %eax, %edx /* Offset -> root if this was MBR */
221 call read_partition_table
223 call scan_partition_table
225 /* This returned, so we need to reload the current partition table */
226 movl 28(%bp), %eax /* "Base" */
227 call read_partition_table
231 /* Not an extended partition */
235 /* Nothing found, return */
240 * boot: invoke the actual bootstrap. (%si) points to the partition
241 * table entry, and 28(%bp) has the partition table base.
246 movl %eax, 8(%si) /* Adjust in-memory partition table entry */
249 cmpw $0xaa55, (bootsec+510)
250 jne missing_os /* Not a valid boot sector */
252 popw %dx /* dl -> drive number */
253 popw %di /* es:di -> $PnP vector */
262 movw $missing_os_msg, %si
265 movw $disk_error_msg, %si
268 movw $too_many_active_msg, %si
277 movb (BIOS_page), %bh
282 int $0x18 /* Boot failure */
286 .ascii "Missing operating system."
289 .ascii "Operating system load error."
292 .ascii "Multiple active partitions."