1 /* -----------------------------------------------------------------------
3 * Copyright 2007-2009 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)
40 /* gas/ld has issues with doing this as absolute addresses... */
41 .section ".bootsec", "a", @nobits
55 pushw %es /* es:di -> $PnP header */
61 /* Copy down to 0:0x600 */
69 /* Escape for the user: if Ctrl is pressed, assume drive hd0 */
70 testb $0x04, BIOS_kbdflags /* Ctrl pressed */
74 pushw %dx /* dl -> drive number */
76 /* Check to see if we have EBIOS */
77 pushw %dx /* drive number */
78 movb $0x41, %ah /* %al == 0 already */
87 shrw %cx /* Bit 0 = fixed disk subset */
90 /* We have EBIOS; patch in the following code at
91 read_sector_cbios: movb $0x42, %ah ; jmp read_common */
92 movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \
98 /* Get (C)HS geometry */
101 andw $0x3f, %cx /* Sector count */
102 pushw %cx /* Save sectors on the stack */
103 movzbw %dh, %ax /* dh = max head */
104 incw %ax /* From 0-based max to count */
105 mulw %cx /* Heads*sectors -> sectors per cylinder */
107 /* Save sectors/cylinder on the stack */
108 pushw %dx /* High word */
109 pushw %ax /* Low word */
111 xorl %eax, %eax /* Base */
112 cdq /* Root (%edx <- 0) */
113 call scan_partition_table
115 /* If we get here, we have no OS */
118 .ascii "Missing operating system.\r\n"
121 * read_sector: read a single sector pointed to by %eax to 0x7c00.
122 * CF is set on error. All registers saved.
128 pushl %edx /* MSW of LBA */
129 pushl %eax /* LSW of LBA */
130 pushw %es /* Buffer segment */
131 pushw %bx /* Buffer offset */
132 pushw $1 /* Sector count */
133 pushw $16 /* Size of packet */
136 /* This chunk is skipped if we have ebios */
137 /* Do not clobber %eax before this chunk! */
138 /* This also relies on %bx and %edx as set up above. */
148 incw %cx /* Sectors are 1-based */
154 leaw 16(%si), %sp /* Drop DAPA */
159 * read_partition_table:
160 * Read a partition table (pointed to by %eax), and copy
161 * the partition table into the ptab buffer.
163 * Clobbers %si, %di, and %cx, other registers preserved.
166 * On error, CF is set and ptab is overwritten with junk.
170 read_partition_table:
172 movw $bootsec+446, %si
179 * scan_partition_table:
180 * Scan a partition table currently loaded in the partition table
181 * area. Preserve all registers.
184 * %eax - base (location of this partition table)
185 * %edx - root (offset from MBR, or 0 for MBR)
187 * These get pushed into stack slots:
188 * 28(%bp) - %eax - base
189 * 20(%bp) - %edx - root
192 scan_partition_table:
196 /* Search for active partitions */
211 decw %ax /* Number of active partitions found */
215 /* No active partitions found, look for extended partitions */
216 popw %cx /* %cx <- 4 */
217 popw %bx /* %bx <- ptab */
220 cmpb $0x0f, %al /* 0x0f = Win9x extended */
222 andb $~0x80, %al /* 0x85 = Linux extended */
223 cmpb $0x05, %al /* 0x05 = MS-DOS extended */
226 /* It is an extended partition. Read the extended partition and
227 try to scan it. If the scan returns, re-load the current
228 partition table and resume scan. */
230 movl 8(%bx), %eax /* Partition table offset */
231 movl 20(%bp), %edx /* "Root" */
232 addl %edx, %eax /* Compute location of new ptab */
233 andl %edx, %edx /* Is this the MBR? */
235 movl %eax, %edx /* Offset -> root if this was MBR */
237 call read_partition_table
239 call scan_partition_table
241 /* This returned, so we need to reload the current partition table */
242 movl 28(%bp), %eax /* "Base" */
243 call read_partition_table
247 /* Not an extended partition */
251 /* Nothing found, return */
257 .ascii "Multiple active partitions.\r\n"
260 * boot: invoke the actual bootstrap. (%si) points to the partition
261 * table entry, and 28(%bp) has the partition table base.
266 movl %eax, 8(%si) /* Adjust in-memory partition table entry */
269 cmpw $0xaa55, (bootsec+510)
270 jne missing_os /* Not a valid boot sector */
271 movw $driveno, %sp /* driveno == bootsec-6 */
272 popw %dx /* dl -> drive number */
273 popw %di /* es:di -> $PnP vector */
276 jmpw *%sp /* %sp == bootsec */
280 .ascii "Operating system load error.\r\n"
283 * Print error messages. This is invoked with "call", with the
284 * error message at the return address.
291 movb (BIOS_page), %bh
293 int $0x10 /* May destroy %bp */
294 cmpb $10, %al /* Newline? */
297 int $0x18 /* Boot failure */