i386/gptzfsboot/gptldr.S

	gptldr.S revision 199767f8919635c4928607450d9e0abb932109ce
/*-
 * Copyright (c) 2007 Yahoo!, Inc.
 * All rights reserved.
 * Written by: John Baldwin <jhb@FreeBSD.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the author nor the names of any co-contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 *
 * Partly from: src/sys/boot/i386/boot2/boot1.S 1.31
 */

/* Memory Locations */
        .set MEM_REL,0x700      # Relocation address
        .set MEM_ARG,0x900      # Arguments
        .set MEM_ORG,0x7c00     # Origin
        .set MEM_BUF,0x8cec     # Load area
        .set MEM_BTX,0x9000     # BTX start
        .set MEM_JMP,0x9010     # BTX entry point
        .set MEM_USR,0xa000     # Client start
        .set BDA_BOOT,0x472     # Boot howto flag

/* Misc. Constants */
        .set SIZ_PAG,0x1000     # Page size
        .set SIZ_SEC,0x200      # Sector size
        .set COPY_BLKS,0x4      # Number of blocks
                        # to copy for boot2
        .set COPY_BLK_SZ,0x8000     # Copy in 32k blocks; must be
                        # a multiple of 16 bytes

        .globl start
        .code16

/*
 * Copy BTX and boot2 to the right locations and start it all up.
 */

/*
 * Setup the segment registers to flat addressing (segment 0) and setup the
 * stack to end just below the start of our code.
 */
start:      xor %cx,%cx         # Zero
        mov %cx,%es         # Address
        mov %cx,%ds         #  data
        mov %cx,%ss         # Set up
        mov $start,%sp          #  stack

/*
 * BTX is right after us at 'end'.  We read the length of BTX out of
 * its header to find boot2.  We need to copy boot2 to MEM_USR and BTX
 * to MEM_BTX.  Since those might overlap, we have to copy boot2
 * backwards first and then copy BTX.  We aren't sure exactly how long
 * boot2 is, but it's currently under 128kB so we'll copy 4 blocks of 32kB
 * each; this can be adjusted via COPY_BLK and COPY_BLK_SZ above.
 */
        mov $end,%bx            # BTX
        mov 0xa(%bx),%si        # Get BTX length and set
        add %bx,%si         #  %si to start of boot2
        dec %si             # Set %ds:%si to point at the
        mov %si,%ax         # last byte we want to copy
        shr $4,%ax          # from boot2, with %si made as
        add $(COPY_BLKS*COPY_BLK_SZ/16),%ax # small as possible.
        and $0xf,%si            #
        mov %ax,%ds         #
        mov $MEM_USR/16,%ax     # Set %es:(-1) to point at
        add $(COPY_BLKS*COPY_BLK_SZ/16),%ax # the last byte we
        mov %ax,%es         # want to copy boot2 into.
        mov $COPY_BLKS,%bx      # Copy COPY_BLKS 32k blocks
copyloop:
        add $COPY_BLK_SZ,%si        # Adjust %ds:%si to point at
        mov %ds,%ax         # the end of the next 32k to
        sub $COPY_BLK_SZ/16,%ax     # copy from boot2
        mov %ax,%ds
        mov $COPY_BLK_SZ-1,%di      # Adjust %es:%di to point at
        mov %es,%ax         # the end of the next 32k into
        sub $COPY_BLK_SZ/16,%ax     # which we want boot2 copied
        mov %ax,%es
        mov $COPY_BLK_SZ,%cx        # Copy 32k
        std
        rep movsb
        dec %bx
        jnz copyloop
        mov %cx,%ds         # Reset %ds and %es
        mov %cx,%es
        mov $end,%bx            # BTX
        mov 0xa(%bx),%cx        # Get BTX length and set
        mov %bx,%si         #  %si to end of BTX
        mov $MEM_BTX,%di        # %di -> end of BTX at
        add %cx,%si         #  MEM_BTX
        add %cx,%di
        dec %si
        dec %di
        rep movsb           # Move BTX
        cld             # String ops inc
/*
 * Enable A20 so we can access memory above 1 meg.
 * Use the zero-valued %cx as a timeout for embedded hardware which do not
 * have a keyboard controller.
 */
seta20:     cli             # Disable interrupts
seta20.1:   dec %cx             # Timeout?
        jz seta20.3         # Yes
        inb $0x64,%al           # Get status
        testb $0x2,%al          # Busy?
        jnz seta20.1            # Yes
        movb $0xd1,%al          # Command: Write
        outb %al,$0x64          #  output port
seta20.2:   inb $0x64,%al           # Get status
        testb $0x2,%al          # Busy?
        jnz seta20.2            # Yes
        movb $0xdf,%al          # Enable
        outb %al,$0x60          #  A20
seta20.3:   sti             # Enable interrupts

/*
 * Save drive number from BIOS so boot2 can see it and start BTX.
 */
        movb %dl,MEM_ARG
        jmp MEM_JMP         # Start BTX
/*
 * make sure the end is aligned for concatenated next module
 */
        .align 4
end: