rt-thread-official/libcpu/ia32/start_gcc.S

/*
 * Copyright (c) 2006-2021, RT-Thread Development Team
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Change Logs:
 * Date           Author       Notes
 * 2006-09-15     QiuYi        The first version.
 * 2012-02-15     aozima       update.
 */

/* the magic number for the multiboot header.  */
#define MULTIBOOT_HEADER_MAGIC		0x1BADB002

/* the flags for the multiboot header.  */
#define MULTIBOOT_HEADER_FLAGS		0x00000003

#define CONFIG_STACKSIZE            8192

/**
 * @addtogroup I386
 */
/*@{*/

.section .init, "ax"

/* the system entry */
.globl _start
_start:
	jmp	multiboot_entry

	/* Align 32 bits boundary.  */
	.align	4

	/* multiboot header.  */
multiboot_header:
	/* magic */
	.long	MULTIBOOT_HEADER_MAGIC
	/* flags */
	.long	MULTIBOOT_HEADER_FLAGS
	/* checksum */
	.long	-(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)

multiboot_entry:
	movl	$(_end + 0x1000),%esp

	/* reset eflags.  */
	pushl	$0
	popf

	/* rebuild globe describe table */
	lgdt	__gdtdesc

	movl	$0x10,%eax
	movw	%ax,%ds
	movw	%ax,%es
	movw	%ax,%ss
	ljmp	$0x08, $relocated

relocated:
	/* push the pointer to the multiboot information structure.  */
	pushl	%ebx

	/* push the magic value.  */
	pushl	%eax

	call	rtthread_startup

	/* never get here */
spin:
	hlt
	jmp	spin

.data
.p2align	2
__gdt:
	.word	0,0,0,0

	.word	0x07FF		/* 8Mb - limit=2047 */
	.word	0x0000
	.word	0x9A00		/* code read/exec */
	.word	0x00C0

	.word	0x07FF		/* 8Mb - limit=2047 */
	.word	0x0000
	.word	0x9200		/* data read/write */
	.word	0x00C0

__gdtdesc:
	.word	0x17
	.long	__gdt

/*@}*/