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Speculative Store Bypass Barrier is a memory barrier which prevents speculative loads from bypassing earlier stores to the same virtual address under certain conditions.
The semantics of the Speculative Store Bypass Barrier are:
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 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |
CRm | opc |
MemBarrierOp op;
MBReqDomain domain;
MBReqTypes types;
case opc of
when '00' op = MemBarrierOp_DSB;
when '01' op = MemBarrierOp_DMB;
when '10' op = MemBarrierOp_ISB;
otherwise
if HaveSBExt() && CRm<3:0> == '0000' then
op = MemBarrierOp_SB;
else
UNDEFINED;
case CRm<3:2> of
when '00' domain = MBReqDomain_OuterShareable;
when '01' domain = MBReqDomain_Nonshareable;
when '10' domain = MBReqDomain_InnerShareable;
when '11' domain = MBReqDomain_FullSystem;
case CRm<1:0> of
when '01' types = MBReqTypes_Reads;
when '10' types = MBReqTypes_Writes;
when '11' types = MBReqTypes_All;
otherwise
if CRm<3:2> == '01' then
op = MemBarrierOp_PSSBB;
elsif CRm<3:2> == '00' && opc == '00' then
op = MemBarrierOp_SSBB;
elsif HaveSBExt() && CRm<3:2> == '00' && opc == '11' then
op = MemBarrierOp_SB;
else
types = MBReqTypes_All;
domain = MBReqDomain_FullSystem// No additional decoding required;
case op of
when MemBarrierOp_DSBDataSynchronizationBarrier(domain, types);
when MemBarrierOp_DMBDataMemoryBarrier(domain, types);
when MemBarrierOp_ISBInstructionSynchronizationBarrier();
when MemBarrierOp_SSBBSpeculativeStoreBypassBarrierToVA();
when MemBarrierOp_PSSBBSpeculativeStoreBypassBarrierToPA();
when MemBarrierOp_SBSpeculationBarrier();
Internal version only: isa v30.41v30.3, AdvSIMD v27.08v27.04, pseudocode r8p5_00bet2_rc5v85-xml-00bet9_rc1_1, sve v8.5-00bet10_rc5v8.5-00bet9_rc1
; Build timestamp: 2019-03-28T062018-12-12T11:3450
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This document is Non-Confidential.
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