保护模式下通过写显存在屏幕上输出字符串

环境：Ubuntu，nasm，bochs

 

asm 文件：

 

%include "common.inc"org 0x7c00jmp LABEL_BEGIN[SECTION .gdt]LABEL_GDT:Descriptor 0, 0, 0LABEL_DESC_CODE32Descriptor 0, SegCode32Len -1, DA_C + DA_32LABEL_DESC_VIDEODescriptor 0xb8000, 0xffff, DA_DRWGdtLen equ $ - LABEL_GDTGdtPtr dw GdtLen - 1 dd 0SelectorCode32 equ LABEL_DESC_CODE32 - LABEL_GDTSelectorVideo equ LABEL_DESC_VIDEO - LABEL_GDT[SECTION .s16][BITS 16]LABEL_BEGIN:mov ax, csmov ds, axmov es, axmov ss, axmov sp, 0x100xor eax, eaxmov ax, csshl eax, 4add eax, LABEL_SEG_CODE32mov word [LABEL_DESC_CODE32 + 2], axshr eax, 16mov byte [LABEL_DESC_CODE32 + 4], almov byte [LABEL_DESC_CODE32 + 7], ahxor eax, eaxmov ax, dsshl eax, 4add eax, LABEL_GDTmov dword [GdtPtr + 2], eaxlgdt [GdtPtr]cliin al, 0x92or al, 00000010bout 92h, almov eax, cr0or eax, 1mov cr0, eaxjmp dword SelectorCode32:0[SECTION .s32][BITS 32]LABEL_SEG_CODE32:mov ax, SelectorVideomov gs, axxor ecx, ecxOutputMsgLoop:inc ecxxor ebx, ebxmov bx, word [Row]add bx, word [Line]add ebx, ecxadd ebx, ecxmov edi, ebxmov ah, 0x0cmov al, byte[MsgBegin + ecx - 1]mov [gs:edi], axcmp ecx, MsgEnd - MsgBeginjnz OutputMsgLoopjmp $MsgBegin: db "Hello World from Proteas"MsgEnd:Row dw 80 * 11 * 2Line dw (79 - (MsgEnd - MsgBegin)) * 2SegCode32Len equ $ - LABEL_SEG_CODE32 

inc 文件：

DA_32EQU4000h;0100 0000 0000 0000DA_DPL0EQU00hDA_DPL1EQU20hDA_DPL2EQU40hDA_DPL3EQU60hDA_DREQU90hDA_DRWEQU92hDA_DRWAEQU93hDA_CEQU98hDA_CREQU9AhDA_CCOEQU9ChDA_CCOREQU9EhDA_LDTEQU82hDA_TaskGateEQU85hDA_386TSSEQU89hDA_386CGateEQU8ChDA_386IGateEQU8EhDA_386TGateEQU8FhSA_RPL0EQU0SA_RPL1EQU1SA_RPL2EQU2SA_RPL3EQU3SA_TIGEQU0SA_TILEQU4; usage: Descriptor Base, Limit, Attr; Base: dd; Limit: dd (low 20 bits available); Attr: dw (lower 4 bits of higher byte are always 0)%macro Descriptor 3dw%2 & 0FFFFh; 段界限1dw%1 & 0FFFFh; 段基址1db(%1 >> 16) & 0FFh; 段基址2dw((%2 >> 8) & 0F00h) | (%3 & 0F0FFh); 属性1 + 段界限2 + 属性2db(%1 >> 24) & 0FFh; 段基址3%endmacro ; 共 8 字节; usage: Gate Selector, Offset, DCount, Attr; Selector: dw; Offset: dd; DCount: db; Attr: db%macro Gate 4dw(%2 & 0FFFFh); 偏移1dw%1; 选择子dw(%3 & 1Fh) | ((%4 << 8) & 0FF00h); 属性dw((%2 >> 16) & 0FFFFh); 偏移2%endmacro ; 共 8 字节 

make 文件：

boot.bin:boot.asm Makefilenasm -o ./bin/boot.bin boot.asmclean:rm -rf ./bin/boot.binimg:dd if=./bin/boot.bin of=./bin/vdisk.img bs=512 count=1 conv=notrunc 

 

经验与教训：在代码段中插入数据，要放入代码段的底部，否则会被当做指令执行。