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      1 /* -----------------------------------------------------------------------
      2  *
      3  *   Copyright 2007-2009 H. Peter Anvin - All Rights Reserved
      4  *   Copyright 2009-2010 Intel Corporation; author: H. Peter Anvin
      5  *
      6  *   Permission is hereby granted, free of charge, to any person
      7  *   obtaining a copy of this software and associated documentation
      8  *   files (the "Software"), to deal in the Software without
      9  *   restriction, including without limitation the rights to use,
     10  *   copy, modify, merge, publish, distribute, sublicense, and/or
     11  *   sell copies of the Software, and to permit persons to whom
     12  *   the Software is furnished to do so, subject to the following
     13  *   conditions:
     14  *
     15  *   The above copyright notice and this permission notice shall
     16  *   be included in all copies or substantial portions of the Software.
     17  *
     18  *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     19  *   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
     20  *   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
     21  *   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
     22  *   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
     23  *   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     24  *   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
     25  *   OTHER DEALINGS IN THE SOFTWARE.
     26  *
     27  * ----------------------------------------------------------------------- */
     28 
     29 #include "adjust.h"
     30 
     31 	.code16
     32 	.text
     33 
     34 	.globl	bootsec
     35 stack		= 0x7c00
     36 
     37 /* Partition table header here */
     38 phdr		= stack		/* Above the stack, overwritten by bootsect */
     39 /* Partition table sector here */
     40 /* To handle > 32K we need to play segment tricks... */
     41 psec		= _phdr + 512
     42 
     43 /* Where we put DS:SI */
     44 dssi_out	= _start + 0x1be
     45 
     46 BIOS_kbdflags	= 0x417
     47 BIOS_page	= 0x462
     48 
     49 	/* gas/ld has issues with doing this as absolute addresses... */
     50 	.section ".bootsec", "a", @nobits
     51 	.globl	bootsec
     52 bootsec:
     53 	.space	512
     54 
     55 	.text
     56 	.globl	_start
     57 _start:
     58 	.byte	0x33, 0xc0	/* xorw	%ax, %ax */
     59 	cli
     60 	movw	%ax, %ds
     61 	movw	%ax, %ss
     62 	movw	$stack, %sp
     63 	movw	%sp, %si
     64 	pushw	%es		/* 4(%bp) es:di -> $PnP header */
     65 	pushw	%di		/* 2(%bp) */
     66 	movw	%ax, %es
     67 	sti
     68 	cld
     69 
     70 	/* Copy down to 0:0x600 */
     71 	movw	$_start, %di
     72 	movw	$(512/2), %cx
     73 	rep; movsw
     74 
     75 	ljmpw	$0, $next
     76 next:
     77 
     78 	ADJUST_DRIVE
     79 	pushw	%dx		/* 0(%bp) = %dl -> drive number */
     80 	movw	%sp, %bp	/* %bp -> frame pointer: LEAVE UNCHANGED */
     81 
     82 	/* prepare to read sector size */
     83 	sub	$0x1c, %sp	/* -28(%bp) == %sp */
     84 	pushw	$0x1e		/* -30(%bp) == %sp */
     85 	movw	$0x200, -6(%bp)	/* -6(%bp) sector size */
     86 
     87 	/* Check to see if we have EBIOS */
     88 	pushw	%dx		/* drive number */
     89 	movb	$0x41, %ah	/* %al == 0 already */
     90 	movw	$0x55aa, %bx
     91 	xorw	%cx, %cx
     92 	xorb	%dh, %dh
     93 	stc
     94 	int	$0x13
     95 	popw	%dx		/* restore drive */
     96 	movb	$0x08, %ah	/* get CHS geometry */
     97 	jc	1f
     98 	cmpw	$0xaa55, %bx
     99 	jne	1f
    100 	shrw	%cx		/* Bit 0 = fixed disk subset */
    101 	jnc	1f
    102 
    103 	/* We have EBIOS; patch in the following code at
    104 	   read_sector_cbios: movb $0x42, %ah ;  jmp read_common */
    105 	movl	$0xeb42b4+((read_common-read_sector_cbios-4) << 24), \
    106 		(read_sector_cbios)
    107 
    108 	/*
    109 	 * read sector size.
    110 	 * Should not fail but if it does I assume that at least
    111 	 * previous 512 value is not overridden
    112 	 */
    113 	movb	$0x48, %ah
    114 	movw	%sp, %si
    115 
    116 1:
    117 	/* Get (C)HS geometry */
    118 	int	$0x13
    119 
    120 	/* here we computer CHS values or just do some dummy computation for EBIOS */
    121 	andw	$0x3f, %cx	/* Sector count */
    122 	pushw	%cx		/* -32(%bp) Save sectors on the stack */
    123 	movzbw	%dh, %ax	/* dh = max head */
    124 	incw	%ax		/* From 0-based max to count */
    125 	mulw	%cx		/* Heads*sectors -> sectors per cylinder */
    126 
    127 	/* Save sectors/cylinder on the stack */
    128 	pushw	%dx		/* -34(%bp) High word */
    129 	pushw	%ax		/* -36(%bp) Low word */
    130 
    131 	/* Load partition table header */
    132 	xorl	%eax,%eax
    133 	cltd
    134 	incw	%ax		/* %edx:%eax = 1 */
    135 	call	read_sector_phdr
    136 
    137 	/* Number of partition sectors */
    138 	/* We assume the partition table is 32K or less */
    139 	movw	(80+6)(%bp),%cx		/* NumberOfPartitionEntries */
    140 	movw	(84+6)(%bp),%ax		/* SizeOfPartitionEntry */
    141 	pushw	%ax
    142 	pushw	%cx
    143 	mulw	%cx
    144 	divw	-6(%bp)	/* %dx == 0 here */
    145 	xchgw	%ax,%cx
    146 	incw	%cx
    147 
    148 	/* Starting LBA of partition array */
    149 	movl	(72+6)(%bp),%eax
    150 	movl	(76+6)(%bp),%edx
    151 
    152 	pushw	%bx
    153 get_ptab:
    154 	call	read_sector
    155 	loopw	get_ptab
    156 
    157 	/* Find the boot partition */
    158 	xorw	%si,%si			/* Nothing found yet */
    159 	popw	%di			/* Partition table in memory */
    160 	popw	%cx			/* NumberOfPartitionEntries */
    161 	popw	%ax			/* SizeOfPartitionEntry */
    162 
    163 find_part:
    164 	/* If the PartitionTypeGUID is all zero, it's an empty slot */
    165 	movl	  (%di),%edx
    166 	orl	 4(%di),%edx
    167 	orl	 8(%di),%edx
    168 	orl	12(%di),%edx
    169 	jz	not_this
    170 	testb	$0x04,48(%di)
    171 	jz	not_this
    172 	andw	%si,%si
    173 	jnz	found_multiple
    174 	movw	%di,%si
    175 not_this:
    176 	addw	%ax,%di
    177 	loopw	find_part
    178 
    179 	andw	%si,%si
    180 	jnz	found_part
    181 
    182 missing_os:
    183 	call	error
    184 	.ascii	"Missing OS\r\n"
    185 
    186 found_multiple:
    187 	call	error
    188 	.ascii	"Multiple active partitions\r\n"
    189 
    190 found_part:
    191 	xchgw	%ax,%cx		/* Set up %cx for rep movsb further down */
    192 
    193 	movw	$dssi_out,%di
    194 	pushw	%di
    195 
    196 	/* 80 00 00 00 ee 00 00 00
    197 	   - bootable partition, type EFI (EE), no CHS information */
    198 	xorl	%eax,%eax
    199 	movb	$0x80,%al
    200 	stosl
    201 	movb	$0xed,%al
    202 	stosl
    203 	movl	32(%si),%eax
    204 	movl	36(%si),%edx
    205 	call	saturate_stosl		/* Partition start */
    206 
    207 	movl	40(%si),%eax
    208 	movl	44(%si),%edx
    209 	subl	32(%si),%eax
    210 	sbbl	36(%si),%edx
    211 	call	inc64
    212 	call	saturate_stosl		/* Partition length */
    213 
    214 	movzwl	%cx,%eax		/* Length of GPT entry */
    215 	stosl
    216 
    217 	rep; movsb			/* GPT entry follows MBR entry */
    218 	popw	%si
    219 
    220 /*
    221  * boot: invoke the actual bootstrap. %ds:%si points to the
    222  * partition information in memory.  The top word on the stack
    223  * is phdr == 0x7c00 == the address of the boot sector.
    224  */
    225 boot:
    226 	movl	(32+20)(%si),%eax
    227 	movl	(36+20)(%si),%edx
    228 	call	read_sector_phdr
    229 	cmpw	$0xaa55, (0x7c00+0x1fe)
    230 	jne	missing_os	/* Not a valid boot sector */
    231 	movw	%bp, %sp	/* driveno == bootsec-6 */
    232 	popw	%dx		/* dl -> drive number */
    233 	popw	%di		/* es:di -> $PnP vector */
    234 	popw	%es
    235 	movl	$0x54504721,%eax /* !GPT magic number */
    236 	cli
    237 	jmpw	*%sp		/* %sp == bootsec */
    238 
    239 /*
    240  * Store the value in %eax to %di iff %edx == 0, otherwise store -1.
    241  * Returns the value that was actually written in %eax.
    242  */
    243 saturate_stosl:
    244 	andl	%edx,%edx
    245 	jz 1f
    246 	orl	$-1,%eax
    247 1:	stosl
    248 	ret
    249 
    250 read_sector_phdr:
    251 	movw	$phdr, %bx
    252 
    253 	/* fall through and read sector */
    254 
    255 /*
    256  * read_sector: read a single sector pointed to by %edx:%eax to
    257  * %es:%bx.  CF is set on error.  All registers saved.
    258  * %edx:%eax and %es:%bx are incremented to read next sector
    259  */
    260 read_sector:
    261 	pushal
    262 	pushl	%edx	/* MSW of LBA */
    263 	pushl	%eax	/* LSW of LBA */
    264 	pushw	%es	/* Buffer segment */
    265 	pushw	%bx	/* Buffer offset */
    266 	pushw	$1	/* Sector count */
    267 	pushw	$16	/* Size of packet */
    268 	movw	%sp, %si
    269 
    270 	/* This chunk is skipped if we have ebios */
    271 	/* Do not clobber %es:%bx or %edx:%eax before this chunk! */
    272 read_sector_cbios:
    273 	divl	-36(%bp)	/* secpercyl */
    274 	shlb	$6, %ah
    275 	movb	%ah, %cl
    276 	movb	%al, %ch
    277 	xchgw	%dx, %ax
    278 	divb	-32(%bp)	/* sectors */
    279 	movb	%al, %dh
    280 	orb	%ah, %cl
    281 	incw	%cx	/* Sectors are 1-based */
    282 	movw	$0x0201, %ax
    283 
    284 read_common:
    285 	movb	(%bp), %dl /* driveno */
    286 	int	$0x13
    287 	leaw	16(%si), %sp	/* Drop DAPA */
    288 	popal
    289 	jc	disk_error
    290 	addb	-5(%bp), %bh		/* bx += sector size: point to the next buffer */
    291 
    292 	/* fall through and increment sector number */
    293 
    294 /*
    295  * Increment %edx:%eax
    296  */
    297 inc64:
    298 	addl	$1,%eax
    299 	adcl	$0,%edx
    300 	ret
    301 
    302 disk_error:
    303 	call	error
    304 	.ascii	"Disk error\r\n"
    305 
    306 /*
    307  * Print error messages.  This is invoked with "call", with the
    308  * error message at the return address.
    309  */
    310 error:
    311 	popw	%si
    312 2:
    313 	lodsb
    314 	movb	$0x0e, %ah
    315 	movb	(BIOS_page), %bh
    316 	movb	$0x07, %bl
    317 	int	$0x10		/* May destroy %bp */
    318 	cmpb	$10, %al	/* Newline? */
    319 	jne	2b
    320 
    321 	int	$0x18		/* Boot failure */
    322 die:
    323 	hlt
    324 	jmp	die
    325