--- /dev/null
+/* -----------------------------------------------------------------------
+ *
+ * Copyright 2007-2008 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.
+ *
+ * ----------------------------------------------------------------------- */
+
+ .code16
+ .text
+
+ .globl bootsec
+stack = 0x7c00
+driveno = (stack-6)
+sectors = (stack-8)
+secpercyl = (stack-12)
+
+/* Partition table header here */
+phdr = _start + 512
+/* Partition table sector here */
+/* To handle > 32K we need to play segment tricks... */
+psec = 0x8000 /* Above the boot sector and stack */
+
+/* BootGUID */
+bootguid = _start + 0x1a8
+/* Where we put DS:SI */
+dssi_out = _start + 0x1be
+
+BIOS_page = 0x462
+
+ /* gas/ld has issues with doing this as absolute addresses... */
+ .section ".bootsec", "a", @nobits
+ .globl bootsec
+bootsec:
+ .space 512
+
+ .text
+ .globl _start
+_start:
+ cli
+ xorw %ax, %ax
+ movw %ax, %ds
+ movw %ax, %ss
+ movw $stack, %sp
+ movw %sp, %si
+ pushw %es /* es:di -> $PnP header */
+ pushw %di
+ pushw %dx /* dl -> drive number */
+ movw %ax, %es
+ sti
+ cld
+
+ /* Copy down to 0:0x600 */
+ movw $_start, %di
+ movw $(512/2), %cx
+ rep; movsw
+
+ ljmpw $0, $next
+
+next:
+ /* Check to see if we have EBIOS */
+ pushw %dx /* drive number */
+ movb $0x41, %ah /* %al == 0 already */
+ movw $0x55aa, %bx
+ xorw %cx, %cx
+ xorb %dh, %dh
+ stc
+ int $0x13
+ jc 1f
+ cmpw $0xaa55, %bx
+ jne 1f
+ shrw %cx /* Bit 0 = fixed disk subset */
+ jnc 1f
+
+ /* We have EBIOS; patch in the following code at
+ read_sector_cbios: movb $0x42, %ah ; jmp read_common */
+ movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \
+ (read_sector_cbios)
+
+1:
+ popw %dx
+
+ /* Get (C)HS geometry */
+ movb $0x08, %ah
+ int $0x13
+ andw $0x3f, %cx /* Sector count */
+ pushw %cx /* Save sectors on the stack */
+ movzbw %dh, %ax /* dh = max head */
+ incw %ax /* From 0-based max to count */
+ mulw %cx /* Heads*sectors -> sectors per cylinder */
+
+ /* Save sectors/cylinder on the stack */
+ pushw %dx /* High word */
+ pushw %ax /* Low word */
+
+ /* Load partition table header */
+ xorl %eax,%eax
+ xorl %edx,%edx
+ incl %eax
+ movw $phdr,%bx
+ call read_sector
+
+ /* Number of partition sectors */
+ /* We assume the partition table is 32K or less, and that
+ the sector size is 512. */
+ movw (phdr+0x80),%cx /* NumberOfPartitionEntries */
+ movw (phdr+0x84),%ax /* SizeOfPartitionEntry */
+ pushw %ax
+ pushw %cx
+ mulw %cx
+ shrw $9,%ax
+ xchgw %ax,%cx
+ incw %cx
+
+ /* Starting LBA of partition array */
+ movl (phdr+0x72),%eax
+ movl (phdr+0x76),%edx
+
+ movw $psec,%bx
+ pushw %bx
+get_ptab:
+ call read_sector
+ addw $512,%bx
+ call inc64
+ loopw get_ptab
+
+ /* Find the boot partition */
+ popw %si /* Partition table in memory */
+ popw %cx /* NumberOfPartitionEntries */
+ popw %ax /* SizeOfPartitionEntry */
+find_part:
+ pushw %cx
+ pushw %si
+ addw $16,%si
+ movw $bootguid,%di
+ movw $8,%cx
+ rep; cmpsw
+ popw %si
+ popw %cx
+ je found_part
+ addw %ax,%si
+ loopw find_part
+
+ call error
+ .ascii "Boot partition not found\r\n"
+
+found_part:
+ movw $dssi_out+16,%di
+ movw %ax,%cx
+ rep; movsb
+ movw $dssi_out,%si
+ movw %si,%di
+ /* 80 00 00 00 ee 00 00 00
+ - bootable partition, type EFI (EE), no CHS information */
+ xorl %eax,%eax
+ movb $0x80,%al
+ stosl
+ movb $0xee,%al
+ stosl
+ movl (40+16)(%si),%eax
+ movl (48+16)(%si),%edx
+ pushl %eax
+ pushl %edx
+ call saturate_stosl /* Partition start */
+
+ subl (32+16)(%si),%eax
+ sbbl (36+16)(%si),%edx
+ call inc64
+ call saturate_stosl /* Partition length */
+
+/*
+ * boot: invoke the actual bootstrap. (%si) points to the
+ * partition information in memory, and the block offset is
+ * on the stack.
+ */
+boot:
+ popl %edx
+ popl %eax
+ call read_sector
+ cmpw $0xaa55, (bootsec+510)
+ jne missing_os /* Not a valid boot sector */
+ movw $driveno, %sp /* driveno == bootsec-6 */
+ popw %dx /* dl -> drive number */
+ popw %di /* es:di -> $PnP vector */
+ popw %es
+ cli
+ jmpw *%sp /* %sp == bootsec */
+
+missing_os:
+ call error
+ .ascii "Operating system not bootable\r\n"
+
+saturate_stosl:
+ pushl %eax
+ andl %edx,%edx
+ jz 1f
+ orl $-1,%eax
+1: stosl
+ popl %eax
+ ret
+
+inc64:
+ addl $1,%eax
+ adcl $0,%edx
+ ret
+
+/*
+ * read_sector: read a single sector pointed to by %edx:%eax to
+ * %es:%bx. CF is set on error. All registers saved.
+ */
+read_sector:
+ pushal
+ pushl %edx /* MSW of LBA */
+ pushl %eax /* LSW of LBA */
+ pushw %es /* Buffer segment */
+ pushw %bx /* Buffer offset */
+ pushw $1 /* Sector count */
+ pushw $16 /* Size of packet */
+ movw %sp, %si
+
+ /* This chunk is skipped if we have ebios */
+ /* Do not clobber %es:%bx or %edx:%eax before this chunk! */
+read_sector_cbios:
+ divl (secpercyl)
+ shlb $6, %ah
+ movb %ah, %cl
+ movb %al, %ch
+ xchgw %dx, %ax
+ divb (sectors)
+ movb %al, %dh
+ orb %ah, %cl
+ incw %cx /* Sectors are 1-based */
+ movw $0x0201, %ax
+
+read_common:
+ movb (driveno), %dl
+ int $0x13
+ addw $16, %sp /* Drop DAPA */
+ popal
+ jc disk_error
+ ret
+
+disk_error:
+ call error
+ .ascii "Disk error on boot\r\n"
+
+/*
+ * Print error messages. This is invoked with "call", with the
+ * error message at the return address.
+ */
+error:
+ popw %si
+2:
+ lodsb
+ movb $0x0e, %ah
+ movb (BIOS_page), %bh
+ movb $0x07, %bl
+ int $0x10 /* May destroy %bp */
+ cmpb $10, %al /* Newline? */
+ jne 2b
+
+ int $0x18 /* Boot failure */
+die:
+ hlt
+ jmp die
projects / profile / ivi / syslinux.git / commitdiff