汇编学习日志——add指令

在学习Intel汇编程序设计时，有下面一段话

The first two lines, because they are directives, contain no executable instructions. But the subsequent lines are assembly language instructions, each 5 bytes long. The hexadecimal values in the second column, such as B8 00010000are the actual instruction
bytes.

TITLE Add and Substract
;This program adds and substracts 32-bit integers.
.386
.model flat,stdcall
.stack 4096
ExitProcess PROTO,dwExitCode:DWORD
DumpRegs PROTO
.code
main PROC
    mov eax,4h
    add ebx,FFh //如果这里为0x7F的话（或者说小于7F），机器码为83 C3 7F，如果大于7F，则为81 C3 00000080
		//如果这里为eax,ecx,edx,小于0x7F 则为83 C0 7F,如果大于0x7F，则为05 00000080
		//所以ebx为基地址寄存器，在加法上，与其他三个寄存器是不同的
    call DumpRegs
	INVOKE ExitProcess,0
main ENDP
END main