什么是 IBT
The ENDBR32 and ENDBR64 (collectively ENDBRANCH) are two new instructions that are used to mark valid indirect CALL/JMP target locations in the program. This instruction is a NOP on legacy processors for backward compatibility.
The processor implements a state machine that tracks indirect JMP and CALL instructions. When one of these instructions is seen, the state machine moves from IDLE to WAIT_FOR_ENDBRANCH state. In WAIT_FOR_ENDBRANCH state the next instruction in the program stream must be an ENDBRANCH. If an ENDBRANCH is not seen the processor causes a control protection fault (#CP), otherwise the state machine moves back to IDLE state.1
ENDBR32 和 ENDBR64（统称为 ENDBRBRANCH）是两个新指令，用于标记程序中有效的间接 CALL/JMP 位置。这一指令是 NOP 的向下兼容。
该处理器实现了一种状态机，能够跟踪间接 JMP/CALL 指令。当其中某个指令执行时，状态机会从 IDLE 移动到 WAIT_FOR_ENDBRANCH 状态。在 WAIT_FOR_ENDBRANCH 状态，程序流中的下一个指令必须是一个 ENDBRANCH。如果一个 ENDBRANCH 对处理器不可见，这会导致一个控制保护错误（#CP），否则状态机会返回到 IDLE 状态。