DSB -- A64

DSB

Data Synchronization Barrier is a memory barrier that ensures the completion of memory accesses, see Data Synchronization Barrier.

This instruction is used by the aliases PSSBB, and SSBB.

It has encodings from 2 classes: Memory barrier and Memory nXS barrier

Memory barrier

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1	1	0	1	0	1	0	1	0	0	0	0	0	0	1	1	0	0	1	1	CRm				1	0	0	1	1	1	1	1
																									opc		Rt

DSB (<option>|#<imm>)

boolean nXS = FALSE; DSBAlias alias; case CRm of when '0000' alias = DSBAlias_SSBB; when '0100' alias = DSBAlias_PSSBB; otherwise alias = DSBAlias_DSB; MBReqDomain domain; 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; MBReqTypes types; case CRm<1:0> of when '00' types = MBReqTypes_All; domain = MBReqDomain_FullSystem; when '01' types = MBReqTypes_Reads; when '10' types = MBReqTypes_Writes; when '11' types = MBReqTypes_All;

Memory nXS barrier
(FEAT_XS)

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1	1	0	1	0	1	0	1	0	0	0	0	0	0	1	1	0	0	1	1	imm2		1	0	0	0	1	1	1	1	1	1
																								op2			Rt

DSB <option>nXS

if !IsFeatureImplemented(FEAT_XS) then UNDEFINED; MBReqTypes types = MBReqTypes_All; boolean nXS = TRUE; DSBAlias alias = DSBAlias_DSB; MBReqDomain domain; case imm2 of when '00' domain = MBReqDomain_OuterShareable; when '01' domain = MBReqDomain_Nonshareable; when '10' domain = MBReqDomain_InnerShareable; when '11' domain = MBReqDomain_FullSystem;

Assembler Symbols

For the memory barrier variant: specifies the limitation on the barrier operation. Values are:

SY: Full system is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. This option is referred to as the full system barrier. Encoded as CRm = 0b1111.
ST: Full system is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 0b1110.
LD: Full system is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as CRm = 0b1101.
ISH: Inner Shareable is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. Encoded as CRm = 0b1011.
ISHST: Inner Shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 0b1010.
ISHLD: Inner Shareable is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as CRm = 0b1001.
NSH: Non-shareable is the required shareability domain, reads and writes are the required access, both before and after the barrier instruction. Encoded as CRm = 0b0111.
NSHST: Non-shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 0b0110.
NSHLD: Non-shareable is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as CRm = 0b0101.
OSH: Outer Shareable is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. Encoded as CRm = 0b0011.
OSHST: Outer Shareable is the required shareability domain, writes are the required access type, both before and after the barrier instruction. Encoded as CRm = 0b0010.
OSHLD: Outer Shareable is the required shareability domain, reads are the required access type before the barrier instruction, and reads and writes are the required access types after the barrier instruction. Encoded as CRm = 0b0001.

All other encodings of "CRm" that are not listed, other than the values 0b0000 and 0b0100, are reserved and can be encoded using the #<imm> syntax. All unsupported and reserved options must execute as a full system barrier operation, but software must not rely on this behavior. For more information on whether an access is before or after a barrier instruction, see Data Memory Barrier (DMB) or see Data Synchronization Barrier (DSB).

Note

The value 0b0000 is used to encode SSBB and the value 0b0100 is used to encode PSSBB.

CRm	<option>
0001	OSHLD
0010	OSHST
0011	OSH
0101	NSHLD
0110	NSHST
0111	NSH
1000	RESERVED
1001	ISHLD
1010	ISHST
1011	ISH
1100	RESERVED
1101	LD
1110	ST
1111	SY

For the memory nXS barrier variant: specifies the limitation on the barrier operation. Values are:

SY: Full system is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. This option is referred to as the full system barrier. Encoded as imm2 = 0b11.
ISH: Inner Shareable is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. Encoded as imm2 = 0b10.
NSH: Non-shareable is the required shareability domain, reads and writes are the required access, both before and after the barrier instruction. Encoded as imm2 = 0b01.
OSH: Outer Shareable is the required shareability domain, reads and writes are the required access types, both before and after the barrier instruction. Encoded as imm2 = 0b00.

imm2	<option>
00	OSH
01	NSH
10	ISH
11	SY

<imm>

Is a 4-bit unsigned immediate, in the range 0 to 15, encoded in the "CRm" field.

Alias Conditions

Alias	Is preferred when
PSSBB	CRm == '0100'
SSBB	CRm == '0000'

Operation

case alias of when DSBAlias_SSBB SpeculativeStoreBypassBarrierToVA(); when DSBAlias_PSSBB SpeculativeStoreBypassBarrierToPA(); when DSBAlias_DSB if IsFeatureImplemented(FEAT_TME) && TSTATE.depth > 0 then FailTransaction(TMFailure_ERR, FALSE); if !nXS && IsFeatureImplemented(FEAT_XS) then nXS = PSTATE.EL IN {EL0, EL1} && IsHCRXEL2Enabled() && HCRX_EL2.FnXS == '1'; DataSynchronizationBarrier(domain, types, nXS); otherwise Unreachable();

Internal version only: aarchmrs v2023-12_rel, pseudocode v2023-12_rel, sve v2023-12_rel ; Build timestamp: 2023-12-15T16:46

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1	1	0	1	0	1	0	1	0	0	0	0	0	0	1	1	0	0	1	1	CRm				1	0	0	1	1	1	1	1
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1	1	0	1	0	1	0	1	0	0	0	0	0	0	1	1	0	0	1	1	CRm				1	0	0	1	1	1	1	1
																									opc		Rt

DSB