asm.s

i386的bootloader源码grub

	/* store new segment */
	movw	0x4(%esp), %ax
	movw	%ax, segment
	shll	$4, %eax

	/* generate linear address */
	addl	%eax, %ebx

	/* set up to pass the partition where stage2 is located in */
	movl	EXT_C(current_partition), %eax
	movl	%eax, (EXT_C(install_partition)-EXT_C(main))(%ebx)

	/* set up to pass the drive where stage2 is located in */
	movb	EXT_C(current_drive), %dl

	/* set up to pass the second sector of stage2 */
	movl	0xc(%esp), %ecx

	call	EXT_C(prot_to_real)
	.code16

	movl	%ecx, %ebp

#ifdef ABSOLUTE_WITHOUT_ASTERISK
	DATA32	ADDR32	ljmp	(offset)
#else
	DATA32	ADDR32	ljmp	*(offset)
#endif

	.code32
#endif /* STAGE1_5 */
	
/*
 *  These next two routines, "real_to_prot" and "prot_to_real" are structured
 *  in a very specific way.  Be very careful when changing them.
 *
 *  NOTE:  Use of either one messes up %eax and %ebp.
 */

ENTRY(real_to_prot)
	.code16
	cli

	/* load the GDT register */
	DATA32	ADDR32	lgdt	gdtdesc

	/* turn on protected mode */
	movl	%cr0, %eax
	orl	$CR0_PE_ON, %eax
	movl	%eax, %cr0

	/* jump to relocation, flush prefetch queue, and reload %cs */
	DATA32	ljmp	$PROT_MODE_CSEG, $protcseg

	/*
	 *  The ".code32" directive only works in GAS, the GNU assembler!
	 *  This gets out of "16-bit" mode.
	 */
	.code32

protcseg:
	/* reload other segment registers */
	movw	$PROT_MODE_DSEG, %ax
	movw	%ax, %ds
	movw	%ax, %es
	movw	%ax, %fs
	movw	%ax, %gs
	movw	%ax, %ss

	/* put the return address in a known safe location */
	movl	(%esp), %eax
	movl	%eax, STACKOFF

	/* get protected mode stack */
	movl	protstack, %eax
	movl	%eax, %esp
	movl	%eax, %ebp

	/* get return address onto the right stack */
	movl	STACKOFF, %eax
	movl	%eax, (%esp)

	/* zero %eax */
	xorl	%eax, %eax

	/* return on the old (or initialized) stack! */
	ret


ENTRY(prot_to_real)
	/* just in case, set GDT */
	lgdt	gdtdesc

	/* save the protected mode stack */
	movl	%esp, %eax
	movl	%eax, protstack

	/* get the return address */
	movl	(%esp), %eax
	movl	%eax, STACKOFF

	/* set up new stack */
	movl	$STACKOFF, %eax
	movl	%eax, %esp
	movl	%eax, %ebp

	/* set up segment limits */
	movw	$PSEUDO_RM_DSEG, %ax
	movw	%ax, %ds
	movw	%ax, %es
	movw	%ax, %fs
	movw	%ax, %gs
	movw	%ax, %ss

	/* this might be an extra step */
	ljmp	$PSEUDO_RM_CSEG, $tmpcseg	/* jump to a 16 bit segment */

tmpcseg:
	.code16

	/* clear the PE bit of CR0 */
	movl	%cr0, %eax
	andl 	$CR0_PE_OFF, %eax
	movl	%eax, %cr0

	/* flush prefetch queue, reload %cs */
	DATA32	ljmp	$0, $realcseg

realcseg:
	/* we are in real mode now
	 * set up the real mode segment registers : DS, SS, ES
	 */
	/* zero %eax */
	xorl	%eax, %eax

	movw	%ax, %ds
	movw	%ax, %es
	movw	%ax, %fs
	movw	%ax, %gs
	movw	%ax, %ss

	/* restore interrupts */
	sti

	/* return on new stack! */
	DATA32	ret

	.code32


/*
 *   int biosdisk_int13_extensions (int ax, int drive, void *dap)
 *
 *   Call IBM/MS INT13 Extensions (int 13 %ax=AX) for DRIVE. DAP
 *   is passed for disk address packet. If an error occurs, return
 *   non-zero, otherwise zero.
 */

ENTRY(biosdisk_int13_extensions)
	pushl	%ebp
	movl	%esp, %ebp

	pushl	%esi
	pushl	%ebx

	/* compute the address of disk_address_packet */
	movl	0x10(%ebp), %eax
	movw	%ax, %si
	xorw	%ax, %ax
	shrl	$4, %eax
	movw	%ax, %cx	/* save the segment to cx */

	/* drive */
	movb	0xc(%ebp), %dl
	/* ax */
	movw	0x8(%ebp), %bx
	/* enter real mode */
	call	EXT_C(prot_to_real)
	
	.code16
	movw	%bx, %ax
	movw	%cx, %ds
	int	$0x13		/* do the operation */
	movb	%ah, %dl	/* save return value */
	/* clear the data segment */
	xorw	%ax, %ax
	movw	%ax, %ds
	/* back to protected mode */
	DATA32	call	EXT_C(real_to_prot)
	.code32

	movb	%dl, %al	/* return value in %eax */

	popl	%ebx
	popl	%esi
	popl	%ebp

	ret
	
/*
 *   int biosdisk_standard (int ah, int drive, int coff, int hoff, int soff,
 *                          int nsec, int segment)
 *
 *   Call standard and old INT13 (int 13 %ah=AH) for DRIVE. Read/write
 *   NSEC sectors from COFF/HOFF/SOFF into SEGMENT. If an error occurs,
 *   return non-zero, otherwise zero.
 */

ENTRY(biosdisk_standard)
	pushl	%ebp
	movl	%esp, %ebp

	pushl	%ebx
	pushl	%edi
	pushl	%esi

	/* set up CHS information */
	movl	0x10(%ebp), %eax
	movb	%al, %ch
	movb	0x18(%ebp), %al
	shlb	$2, %al
	shrw	$2, %ax
	movb	%al, %cl
	movb	0x14(%ebp), %dh
	/* drive */
	movb	0xc(%ebp), %dl
	/* segment */
	movw	0x20(%ebp), %bx
	/* save nsec and ah to %di */
	movb	0x8(%ebp), %ah
	movb	0x1c(%ebp), %al
	movw	%ax, %di
	/* enter real mode */
	call	EXT_C(prot_to_real)

	.code16
	movw	%bx, %es
	xorw	%bx, %bx
	movw	$3, %si		/* attempt at least three times */

1:	
	movw	%di, %ax
	int	$0x13		/* do the operation */
	jnc	2f		/* check if successful */

	movb	%ah, %bl	/* save return value */
	/* if fail, reset the disk system */
	xorw	%ax, %ax
	int	$0x13
	
	decw	%si
	cmpw	$0, %si
	je	2f
	xorb	%bl, %bl
	jmp	1b		/* retry */
2:	
	/* back to protected mode */
	DATA32	call	EXT_C(real_to_prot)
	.code32

	movb	%bl, %al	/* return value in %eax */
	
	popl	%esi
	popl	%edi
	popl	%ebx
	popl	%ebp

	ret


/*
 *   int check_int13_extensions (int drive)
 *
 *   Check if LBA is supported for DRIVE. If it is supported, then return
 *   the major version of extensions, otherwise zero.
 */

ENTRY(check_int13_extensions)
	pushl	%ebp
	movl	%esp, %ebp

	pushl	%ebx

	/* drive */
	movb	0x8(%ebp), %dl
	/* enter real mode */
	call	EXT_C(prot_to_real)

	.code16
	movb	$0x41, %ah
	movw	$0x55aa, %bx
	int	$0x13		/* do the operation */
	
	/* check the result */
	jc	1f
	cmpw	$0xaa55, %bx
	jne	1f

	movb	%ah, %bl	/* save the major version into %bl */

	/* check if AH=0x42 is supported if FORCE_LBA is zero */
	movb	EXT_C(force_lba), %al
	testb	%al, %al
	jnz	2f
	andw	$1, %cx
	jnz	2f
	
1:
	xorb	%bl, %bl
2:
	/* back to protected mode */
	DATA32	call	EXT_C(real_to_prot)
	.code32

	movb	%bl, %al	/* return value in %eax */

	popl	%ebx
	popl	%ebp

	ret


/*
 *   int get_diskinfo_standard (int drive, unsigned long *cylinders, 
 *                              unsigned long *heads, unsigned long *sectors)
 *
 *   Return the geometry of DRIVE in CYLINDERS, HEADS and SECTORS. If an
 *   error occurs, then return non-zero, otherwise zero.
 */

ENTRY(get_diskinfo_standard)
	pushl	%ebp
	movl	%esp, %ebp

	pushl	%ebx
	pushl	%edi

	/* drive */
	movb	0x8(%ebp), %dl
	/* enter real mode */
	call	EXT_C(prot_to_real)

	.code16
	movb	$0x8, %ah
	int	$0x13		/* do the operation */
	/* check if successful */
	testb	%ah, %ah
	jnz	1f
	/* bogus BIOSes may not return an error number */
	testb	$0x3f, %cl	/* 0 sectors means no disk */
	jnz	1f		/* if non-zero, then succeed */
	/* XXX 0x60 is one of the unused error numbers */
	movb	$0x60, %ah
1:
	movb	%ah, %bl	/* save return value in %bl */
	/* back to protected mode */
	DATA32	call	EXT_C(real_to_prot)
	.code32

	/* restore %ebp */
	leal	0x8(%esp), %ebp
	
	/* heads */
	movb	%dh, %al
	incl	%eax		/* the number of heads is counted from zero */
	movl	0x10(%ebp), %edi
	movl	%eax, (%edi)

	/* sectors */
	xorl	%eax, %eax
	movb	%cl, %al
	andb	$0x3f, %al
	movl	0x14(%ebp), %edi
	movl	%eax, (%edi)

	/* cylinders */
	shrb	$6, %cl
	movb	%cl, %ah
	movb	%ch, %al
	incl	%eax		/* the number of cylinders is 
				   counted from zero */
	movl	0xc(%ebp), %edi
	movl	%eax, (%edi)

	xorl	%eax, %eax
	movb	%bl, %al	/* return value in %eax */

	popl	%edi
	popl	%ebx
	popl	%ebp

	ret


#if 0		
/*
 *   int get_diskinfo_floppy (int drive, unsigned long *cylinders, 
 *                            unsigned long *heads, unsigned long *sectors)
 *
 *   Return the geometry of DRIVE in CYLINDERS, HEADS and SECTORS. If an
 *   error occurs, then return non-zero, otherwise zero.
 */

ENTRY(get_diskinfo_floppy)
	pushl	%ebp
	movl	%esp, %ebp

	pushl	%ebx
	pushl	%esi

	/* drive */
	movb	0x8(%ebp), %dl
	/* enter real mode */
	call	EXT_C(prot_to_real)

	.code16
	/* init probe value */
	movl	$probe_values-1, %esi
1:
	xorw	%ax, %ax
	int	$0x13		/* reset floppy controller */

	incw	%si
	movb	(%si), %cl
	cmpb	$0, %cl		/* probe failed if zero */
	je	2f

	/* perform read */
	movw	$SCRATCHSEG, %ax
	movw	%ax, %es
	xorw	%bx, %bx
	movw	$0x0201, %ax
	movb	$0, %ch
	movb	$0, %dh
	int	$0x13

	/* FIXME: Read from floppy may fail even if the geometry is correct.
	   So should retry at least three times.  */
	jc	1b		/* next value */
	
	/* succeed */
	jmp	2f
	
probe_values:
	.byte	36, 18, 15, 9, 0
	
2:
	/* back to protected mode */
	DATA32	call	EXT_C(real_to_prot)
	.code32

	/* restore %ebp */
	leal	0x8(%esp), %ebp
	
	/* cylinders */
	movl	0xc(%ebp), %eax
	movl	$80, %ebx
	movl	%ebx, (%eax)
	/* heads */
	movl	0x10(%ebp), %eax
	movl	$2, %ebx
	movl	%ebx, (%eax)
	/* sectors */
	movl	0x14(%ebp), %eax
	movzbl	%cl, %ebx
	movl	%ebx, (%eax)

	/* return value in %eax */
	xorl	%eax, %eax
	cmpb	$0, %cl
	jne	3f
	incl	%eax		/* %eax = 1 (non-zero) */
3:
	popl	%esi
	popl	%ebx
	popl	%ebp

	ret
#endif
	

/* Source files are splitted, as they have different copyrights.  */
#ifndef STAGE1_5
# include "setjmp.S"
# include "apm.S"
#endif /* ! STAGE1_5 */
		
	

#ifndef STAGE1_5
/* get_code_end() :  return the address of the end of the code
 * This is here so that it can be replaced by asmstub.c.
 */
ENTRY(get_code_end)
	/* will be the end of the bss */
# if defined(HAVE_END_SYMBOL)
	movl	$end, %eax
# elif defined(HAVE_USCORE_END_SYMBOL)
	movl	$_end, %eax
# endif
	shrl	$2, %eax		/* Round up to the next word. */
	incl	%eax
	shll	$2, %eax
	ret
#endif /* ! STAGE1_5 */

/*
 *
 * get_memsize(i) :  return the memory size in KB. i == 0 for conventional
 *		memory, i == 1 for extended memory
 *	BIOS call "INT 12H" to get conventional memory size
 *	BIOS call "INT 15H, AH=88H" to get extended memory size
 *		Both have the return value in AX.
 *
 */

ENTRY(get_memsize)
	push	%ebp
	push	%ebx

	mov	0xc(%esp), %ebx

	call	EXT_C(prot_to_real)	/* enter real mode */
	.code16

	cmpb	$0x1, %bl
	DATA32	je	xext

	int	$0x12
	DATA32	jmp	xdone

xext:
	movb	$0x88, %ah
	int	$0x15

xdone:
	movw	%ax, %bx

	DATA32	call	EXT_C(real_to_prot)
	.code32

	movw	%bx, %ax
	pop	%ebx
	pop	%ebp
	ret


#ifndef STAGE1_5

/*
 *
 * get_eisamemsize() :  return packed EISA memory map, lower 16 bits is
 *		memory between 1M and 16M in 1K parts, upper 16 bits is
 *		memory above 16M in 64K parts.  If error, return -1.
 *	BIOS call "INT 15H, AH=E801H" to get EISA memory map,
 *		AX = memory between 1M and 16M in 1K parts.
 *		BX = memory above 16M in 64K parts.
 *
 */

ENTRY(get_eisamemsize)
	push	%ebp
	push	%ebx

	call	EXT_C(prot_to_real)	/* enter real mode */
	.code16

	movw	$0xe801, %ax
	int	$0x15

	shll	$16, %ebx
	movw	%ax, %bx

	DATA32	call	EXT_C(real_to_prot)
	.code32

	movl	$0xFFFFFFFF, %eax
	cmpb	$0x86, %bh
	je	xnoteisa

	movl	%ebx, %eax

xnoteisa:
	pop	%ebx
	pop	%ebp
	ret

/*
 *
 * get_mmap_entry(addr, cont) :  address and old continuation value (zero to
 *		start), for the Query System Address Map BIOS call.
 *
 *  Sets the first 4-byte int value of "addr" to the size returned by
 *  the call.  If the call fails, sets it to zero.
 *
 *	Returns:  new (non-zero) continuation value, 0 if done.
 *
 * NOTE: Currently hard-coded for a maximum buffer length of 1024.
 */

ENTRY(get_mmap_entry)
	push	%ebp
	push	%ebx
	push	%edi
	push	%esi

	/* place address (+4) in ES:DI */
	movl	0x14(%esp), %eax
	addl	$4, %eax
	movl	%eax, %edi
	andl	$0xf, %edi
	shrl	$4, %eax
	movl	%eax, %esi

	/* set continuation value */
	movl	0x18(%esp), %ebx

	/* set default maximum buffer size */
	movl	$0x14, %ecx

	/* set EDX to 'SMAP' */
	movl	$0x534d4150, %edx

	call	EXT_C(prot_to_real)	/* enter real mode */
	.code16

	movw	%si, %es
	movl	$0xe820, %eax
	int	$0x15

	DATA32	jc	xnosmap

	cmpl	$0x534d4150, %eax
	DATA32	jne	xnosmap

	cmpl	$0x14, %ecx
	DATA32	jl	xnosmap

	cmpl	$0x400, %ecx
	DATA32	jg	xnosmap

	DATA32	jmp	xsmap

xnosmap:
	movl	$0, %ecx

xsmap:
	DATA32	call	EXT_C(real_to_prot)
	.code32

	/* write length of buffer (zero if error) into "addr" */
	movl	0x14(%esp), %eax
	movl	%ecx, (%eax)

	/* set return value to continuation */
	movl	%ebx, %eax

	pop	%esi
	pop	%edi
	pop	%ebx
	pop	%ebp
	ret

/*
 * get_rom_config_table()
 *
 * Get the linear address of a ROM configuration table. Return zero,
 * if fails.
 */
	
ENTRY(get_rom_config_table)
	pushl	%ebp
	pushl	%ebx

	/* zero %ebx for simplicity */
	xorl	%ebx, %ebx
	
	call	EXT_C(prot_to_real)
	.code16

	movw	$0xc0, %ax
	int	$0x15

	jc	no_rom_table
	testb	%ah, %ah
	jnz	no_rom_table
	
	movw	%es, %dx
	jmp	found_rom_table
	
no_rom_table:
	xorw	%dx, %dx
	xorw	%bx, %bx
	
found_rom_table:
	DATA32	call	EXT_C(real_to_prot)
	.code32

	/* compute the linear address */
	movw	%dx, %ax
	shll	$4, %eax
	addl	%ebx, %eax

	popl	%ebx
	popl	%ebp
	ret


/*
 * int get_vbe_controller_info (struct vbe_controller *controller_ptr)
 *
 * Get VBE controller information.
 */

ENTRY(get_vbe_controller_info)
	pushl	%ebp
	movl	%esp, %ebp
	
	pushl	%edi
	pushl	%ebx

	/* Convert the linear address to segment:offset */
	movl	8(%ebp), %eax
	movl	%eax, %edi
	andl	$0x0000000f, %edi
	shrl	$4, %eax
	movl	%eax, %ebx

	call	EXT_C(prot_to_real)
	.code16

	movw	%bx, %es
	movw	$0x4F00, %ax
	int	$0x10

	movw	%ax, %bx
	DATA32	call	EXT_C(real_to_prot)
	.code32

	movzwl	%bx, %eax

	popl	%ebx
	popl	%edi
	popl	%ebp
	ret

	
/*
 * int get_vbe_mode_info (int mode_number, struct vbe_mode *mode_ptr)
 *
 * Get VBE mode information.
 */

ENTRY(get_vbe_mode_info)
	pushl	%ebp
	movl	%esp, %ebp
	
	pushl	%edi
	pushl	%ebx

	/* Convert the linear address to segment:offset */
	movl	0xc(%ebp), %eax
	movl	%eax, %edi
	andl	$0x0000000f, %edi
	shrl	$4, %eax
	movl	%eax, %ebx

	/* Save the mode number in %cx */
	movl	0x8(%ebp), %ecx
	
	call	EXT_C(prot_to_real)
	.code16

	movw	%bx, %es
	movw	$0x4F01, %ax
	int	$0x10

	movw	%ax, %bx
	DATA32	call	EXT_C(real_to_prot)
	.code32

	movzwl	%bx, %eax

	popl	%ebx
	popl	%edi
	popl	%ebp
	ret