Consumption of Speculative Data Barrier is a memory barrier that controls speculative execution and data value prediction.
No instruction other than branch instructions appearing in program order after the CSDB can be speculatively executed using the results of any:
For purposes of the definition of CSDB, PSTATE.{N,Z,C,V} is not considered a data value. This definition permits:
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1 | 1 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |
CRm | op2 |
SystemHintOp op; case CRm:op2 of when '0000 000' op = SystemHintOp_NOP; when '0000 001' op = SystemHintOp_YIELD; when '0000 010' op = SystemHintOp_WFE; when '0000 011' op = SystemHintOp_WFI; when '0000 100' op = SystemHintOp_SEV; when '0000 101' op = SystemHintOp_SEVL; when '0000 110' if !HaveDGHExt() then EndOfInstruction(); // Instruction executes as NOP op = SystemHintOp_DGH; when '0000 111' SEE "XPACLRI"; when '0001 xxx' case op2 of when '000' SEE "PACIA1716"; when '010' SEE "PACIB1716"; when '100' SEE "AUTIA1716"; when '110' SEE "AUTIB1716"; otherwise EndOfInstruction(); // Instruction executes as NOP when '0010 000' if !HaveRASExt() then EndOfInstruction(); // Instruction executes as NOP op = SystemHintOp_ESB; when '0010 001' if !HaveStatisticalProfiling() then EndOfInstruction(); // Instruction executes as NOP op = SystemHintOp_PSB; when '0010 010' if !HaveSelfHostedTrace() then EndOfInstruction(); // Instruction executes as NOP op = SystemHintOp_TSB; when '0010 100' op = SystemHintOp_CSDB; when '0011 xxx' case op2 of when '000' SEE "PACIAZ"; when '001' SEE "PACIASP"; when '010' SEE "PACIBZ"; when '011' SEE "PACIBSP"; when '100' SEE "AUTIAZ"; when '101' SEE "AUTHASP"; when '110' SEE "AUTIBZ"; when '111' SEE "AUTIBSP"; when '0100 xx0' op = SystemHintOp_BTI; // Check branch target compatibility between BTI instruction and PSTATE.BTYPE SetBTypeCompatible(BTypeCompatible_BTI(op2<2:1>)); otherwise EndOfInstruction(); // Instruction executes as NOP
case op of when SystemHintOp_YIELD Hint_Yield(); when SystemHintOp_DGH Hint_DGH(); when SystemHintOp_WFE if IsEventRegisterSet() then ClearEventRegister(); else trap = FALSE; if PSTATE.EL == EL0 then // Check for traps described by the OS which may be EL1 or EL2. if HaveTWEDExt() then sctlr = SCTLR[]; trap = sctlr.nTWE == '0'; target_el = EL1; else AArch64.CheckForWFxTrap(EL1, TRUE); if !trap && PSTATE.EL IN {EL0, EL1} && EL2Enabled() && !IsInHost() then // Check for traps described by the Hypervisor. if HaveTWEDExt() then trap = HCR_EL2.TWE == '1'; target_el = EL2; else AArch64.CheckForWFxTrap(EL2, TRUE); if !trap && HaveEL(EL3) && PSTATE.EL != EL3 then // Check for traps described by the Secure Monitor. if HaveTWEDExt() then trap = SCR_EL3.TWE == '1'; target_el = EL3; else AArch64.CheckForWFxTrap(EL3, TRUE); if HaveTWEDExt() && trap && PSTATE.EL != EL3 then (delay_enabled, delay) = WFETrapDelay(target_el); // (If trap delay is enabled, Delay amount) if !AArch64.WaitForEventUntilDelay(delay_enabled, delay) then // Event did not arrive until delay expired AArch64.WFxTrap(target_el, TRUE); // Trap WFE else WaitForEvent(); when SystemHintOp_WFI if !InterruptPending() then if PSTATE.EL == EL0 then // Check for traps described by the OS which may be EL1 or EL2. AArch64.CheckForWFxTrap(EL1, FALSE); if PSTATE.EL IN {EL0, EL1} && EL2Enabled() && !IsInHost() then // Check for traps described by the Hypervisor. AArch64.CheckForWFxTrap(EL2, FALSE); if HaveEL(EL3) && PSTATE.EL != EL3 then // Check for traps described by the Secure Monitor. AArch64.CheckForWFxTrap(EL3, FALSE); WaitForInterrupt(); when SystemHintOp_SEV SendEvent(); when SystemHintOp_SEVL SendEventLocal(); when SystemHintOp_ESB if HaveTME() && TSTATE.depth > 0 then FailTransaction(TMFailure_ERR, FALSE); 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 v32.03, AdvSIMD v29.02, pseudocode v2020-03, sve v2020-03_rc1 ; Build timestamp: 2020-04-15T13:33
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