i16_crt0.s

GNU Mach 微内核源代码, 基于美国卡内基美隆大学的 Mach 研究项目

/* 
 * Copyright (c) 1995-1994 The University of Utah and
 * the Computer Systems Laboratory at the University of Utah (CSL).
 * All rights reserved.
 *
 * Permission to use, copy, modify and distribute this software is hereby
 * granted provided that (1) source code retains these copyright, permission,
 * and disclaimer notices, and (2) redistributions including binaries
 * reproduce the notices in supporting documentation, and (3) all advertising
 * materials mentioning features or use of this software display the following
 * acknowledgement: ``This product includes software developed by the
 * Computer Systems Laboratory at the University of Utah.''
 *
 * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
 * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF
 * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * CSL requests users of this software to return to [e-mail] any
 * improvements that they make and grant CSL redistribution rights.
 *
 *      Author: Bryan Ford, University of Utah CSL
 */

#include <mach/machine/asm.h>

#include "config.h"
#include "i16_crt0.h"

	.code16
	.text

ENTRY(i16_entry)
	/* DOS starts us up with our stack pointer pointing
	   to the very top of our BSS segment.
	   ds and es point to the PSP.  */

#define DELAY jmp 1f; 1: jmp 1f; 1: jmp 1f; 1:

	/* Check to make sure we're running on a 386 or higher -
	   _without_ using any 32-bit instructions of course.
	   Tricky, since gas doesn't support 16-bit addressing modes. :-)
	   We can't produce any 16-bit relocations either,
	   because ELF doesn't support them.
	   This code is basically straight out of the Pentium manual,
	   except gassed of coursed.  */
	pushfw
	DELAY
	popw	%bx
	movw	$0xfff,%ax
	andw	%bx,%ax
	pushw	%ax
	DELAY
	popfw
	DELAY
	pushfw
	DELAY
	popw	%ax
	and	$0xf000,%ax
	cmpw	$0xf000,%ax

	je	1f
	orw	$0xf000,%bx
	pushw	%bx
	DELAY
	popfw
	DELAY
	pushfw
	DELAY
	popw	%ax
	andw	$0xf000,%ax
	jnz	4f
1:
	/* Gak!  We're running on an 8086/8088/80286!  */
	callw	5f
	.ascii	"This program requires a 386 or better.\r\n\0"
5:	popw	%si
	movw	%cs,%ax
	movw	%ax,%ds
	cld
2:	lodsb
	orb	%al,%al
	jz	3f
	movb	$0x02,%ah
	movb	%al,%dl
	int	$0x21
	jmp	2b
3:	movw	$0x4c02,%ax
	int	$0x21
4:
	/* Now we can use 32-bit instructions all we want.  */

	/* Save the PSP segment address (dx).  */
	movw	%ds,%dx

	/* Find our real-mode code segment (ax).  */
	movw	%cs,%ax

#ifdef ENABLE_PAGE_ALIGNED_KERNEL
	/* Move our code and data so that everything is on a page boundary.
	   Theoretically we _could_ go past the end of available memory,
	   since we're not checking, but it's enormously unlikely.  */
	std
	movw	%ax,%ds
	addw	$0xff,%ax
	andw	$0xff00,%ax
	movw	%ax,%es
	movl	$EXT(edata),%ecx
	subl	$EXT(i16_entry_2),%ecx
	movl	$EXT(edata)-1,%esi
	movw	%si,%di
	rep
	movsb

	/* Start running at the new address.  */
	pushl	$EXT(i16_entry_2)
	movw	%ax,2(%esp)
	lretw

ENTRY(i16_entry_2)
	/* We're now page aligned.  */
#endif ENABLE_PAGE_ALIGNED_KERNEL

	/* Load the data segment registers appropriately.  */
	movw	%ax,%es
	movw	%ax,%ss

	/* Start using a real stack.  */
	movl	$EXT(crt0_stack)+CRT0_STACK_SIZE,%esp

	/* Clear our BSS segment.  */
	movl	$EXT(edata),%edi
	movl	$EXT(end),%ecx
	subw	%di,%cx
	xorb	%al,%al
	cld
	rep
	stosb

	/* Find the size of the environment array (si) 
	   and the number of environment variables plus one (bx).
	   The PSP segment is still in dx.  */
	movw	%dx,%ds
	movw	0x2c,%ds
	xorw	%si,%si
1:	lodsb
	orb	%al,%al
	jnz	1b
	lodsb
	orb	%al,%al
	jnz	1b

	/* Allocate space for the environment array on the stack.
	   Also make sure the top 16 bits of ESP are cleared,
	   and that the stack pointer is longword aligned.  */
	subw	%si,%sp
	andl	$0x0000fffc,%esp

	/* Copy the environment array to the local stack.
	   We present it backwards, but big deal - shouldn't matter.  */
	xorl	%edi,%edi
	movw	%sp,%di
	xorl	%esi,%esi
	pushl	%esi
	jmp	3f
2:	pushl	%edi
	stosb
1:	lodsb
	stosb
	orb	%al,%al
	jnz	1b
3:	lodsb
	orb	%al,%al
	jnz	2b
	movl	%esp,%cs:EXT(environ)

	/* Copy the program name to the local stack;
	   it will be used as argv[0].  */
	lodsw
	movw	%si,%bx
1:	pushw	$0
	lodsb
	orb	%al,%al
	jz	2f
	lodsb
	orb	%al,%al
	jnz	1b
2:	movw	%bx,%si
	movw	%sp,%di
3:	lodsb
	stosb
	orb	%al,%al
	jnz	3b
	movl	%esp,%ebp

	/* Build argv[1..n] from the command tail in the PSP.
	   Count the arguments in ebx.  */
	movw	%dx,%ds
	xorl	%ecx,%ecx
	xorl	%ebx,%ebx
	movb	0x80,%cl	/* get size of command tail */
	incw	%cx		/* plus the return character */
	movw	$0x80,%si
	addw	%cx,%si		/* si = ptr to return character */
	movw 	%sp,%di
	decw	%di
	subw	%cx,%sp		/* allocate space on the stack */
	andw	$0xfffc,%sp
	pushl	%ebx
	std
1:	xorb	%al,%al		/* store a null terminator for this arg */
	stosb
	incl	%ebx
2:	cmpw	$0x80,%si
	je	5f
	lodsb			/* scan backwards for the end of an arg */
	cmpb	$0x20,%al
	jbe	2b
3:	stosb			/* copy the arg */
	cmpw	$0x80,%si
	je	4f
	lodsb
	cmpb	$0x20,%al
	ja	3b
4:	movw	%di,%cx		/* push an arg pointer */
	incw	%cx
	pushl	%ecx
	jmp	1b
5:

	/* Push the argv[0] pointer.  */
	pushl	%ebp

	/* Push the argument and envirnonment parameters on the stack.  */
	movl	%esp,%eax
	pushl	%cs:EXT(environ)
	pushl	%eax
	pushl	%ebx

	/* Release all conventional memory above the top of our BSS.
	   The PSP segment is still in dx.  */
	movl	$EXT(end)+15,%ebx
	shrw	$4,%bx
	movw	%cs,%ax
	addw	%ax,%bx
	subw	%dx,%bx
	movw	%dx,%es
	movb	$0x4a,%ah
	int	$0x21

	/* Load the normal data segment registers.  */
	movw	%cs,%ax
	movw	%ax,%ds
	movw	%ax,%es

	/* GCC wants the direction flag cleared at all times.  */
	cld

	/* Initialize the bss and run the program.  */
	call	EXT(i16_main)

	.globl	EXT(crt0_stack)
	.comm	EXT(crt0_stack),CRT0_STACK_SIZE

	.globl	EXT(environ)
	.comm	EXT(environ),4


	.data

	.section .anno,"aw",@progbits
	P2ALIGN(4)
	.globl	__ANNO_START__
__ANNO_START__: