x86 - 设置、清除 OF 和 TF 标志的汇编指令

Question

是否有任何汇编指令可以让我们直接“设置”或“清除”Intel 8086 16位标志寄存器中的“OF”和“TF”标志？如果不是，我们应该使用什么伪代码？

Answer 1

http://en.wikipedia.org/wiki/Trap_flag

The 8086 has no instruction to directly set or reset the trap flag. These operations are done by pushing the flag register on the stack, changing the trap flag bit to what the programmer wants it to be, and then popping the flag register back off the stack. The instructions to set the trap flag are:

PUSHF ; Push flags on stack
MOV BP,SP  ; Copy SP to BP for use as index
OR WORD PTR[BP+0],0100H ; Set TF flag
POPF  ; Restore flag Register

To reset the trap flag, simply replace the OR instruction in the preceding sequence with the instruction:

AND WORD PTR[BP+0],0FEFFH

要设置和清除溢出标志，您可以执行相同的操作，将 0100H 替换为 0800H，将 0FEFFh 替换为 0F7FFh.

在设置之前，请务必了解 TF 的作用。这是一个陷阱。