crt0.s

来自「一个微型操作系统源码」· S 代码 · 共 73 行

%macro	EXPORT	1
%ifdef UNDERBARS
	GLOBAL %1
	%1:
%else
	GLOBAL _%1
	_%1:
%endif
%endmacro

%macro	IMPORT 1
%ifdef UNDERBARS
	EXTERN _%1	; use this for GCC with DOS (DJGPP; COFF)
	%define %1 _%1
%else
	EXTERN %1	; use this for GCC with Linux (ELF)
%endif
%endmacro

	SECTION	.text
	EXPORT start
	
	jmp	boot_entry

	ALIGN	4
	EXTERN	_edata
	EXTERN	_end
boot_hdr:
	dd	0x1BADB002
	dd	0x00010000
	dd	0-0x1BADB002-0x00010000
	dd	boot_hdr
	dd	_start
	dd	_bss_start
	dd	_end
	dd	boot_entry

boot_entry:
	
	; ebx holds a pointer to
	; the multiboot info block
	
	mov	esp,boot_stack
	
	push	dword 0
	popf

; zero the kernel BSS
IMPORT _bss_start
IMPORT _end
	xor 	eax,eax
	mov	edi,_bss_start
	mov	ecx,_end
	sub	ecx,edi
	shr	ecx,2
	rep	stosd

	push	ebx		; save parameter for main

	IMPORT main
	call main	
	jmp	short $		; Hang


	SECTION	.bss
	ALIGNB	16
%IFDEF DEBUG
	RESB	4096
%ELSE
	RESB	1024
%ENDIF
boot_stack: