Branch Target Identification. A BTI instruction is used to guard against the execution of instructions which are not the intended target of a branch.
Outside of a guarded memory region, a BTI instruction executes as a NOP. Within a guarded memory region while PSTATE.BTYPE != 0b00, a BTI instruction compatible with the current value of PSTATE.BTYPE will not generate a Branch Target Exception and will allow execution of subsequent instructions within the memory region.
The operand <targets> passed to a BTI instruction determines the values of PSTATE.BTYPE which the BTI instruction is compatible with.
Within a guarded memory region, when PSTATE.BTYPE != 0b00, all instructions will generate a Branch Target Exception, other than BRK, BTI, HLT, PACIASP, and PACIBSP, which might not. See the individual instructions for more information.
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
1 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | x | x | 0 | 1 | 1 | 1 | 1 | 1 |
CRm | op2 |
BTI {<targets>}
SystemHintOp op; if CRm:op2 == '0100 xx0' then op = SystemHintOp_BTI; // Check branch target compatibility between BTI instruction and PSTATE.BTYPE SetBTypeCompatible(BTypeCompatible_BTI(op2<2:1>)); else EndOfInstruction();
<targets> |
Is the type of indirection,
encoded in
|
case op of when SystemHintOp_YIELD Hint_Yield(); when SystemHintOp_DGH Hint_DGH(); when SystemHintOp_WFE Hint_WFE(-1, WFxType_WFE); when SystemHintOp_WFI Hint_WFI(-1, WFxType_WFI); when SystemHintOp_SEV SendEvent(); when SystemHintOp_SEVL SendEventLocal(); when SystemHintOp_ESB SynchronizeErrors(); AArch64.ESBOperation(); if PSTATE.EL IN {EL0, EL1} && EL2Enabled() then AArch64.vESBOperation(); TakeUnmaskedSErrorInterrupts(); when SystemHintOp_PSB ProfilingSynchronizationBarrier(); when SystemHintOp_TSB TraceSynchronizationBarrier(); when SystemHintOp_CSDB ConsumptionOfSpeculativeDataBarrier(); when SystemHintOp_BTI SetBTypeNext('00'); otherwise // do nothing
Internal version only: isa v32.21, AdvSIMD v29.05, pseudocode v2021-06_xml, sve v2021-06_rc2b ; Build timestamp: 2021-06-28T17:02
Copyright © 2010-2021 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.