pssbb

Physical Speculation Barrier

PSSBB

Prevents speculation on physical resources.

Details

Issues a Physical Speculation Barrier to prevent speculation through the barrier on physical resources, typically used to mitigate certain transient execution side-channel attacks. This AArch64-only hint instruction does not modify any condition flags and has no visible register side effects; it may be a no-op on some implementations but carries architectural implications for speculation control. Introduced in ARMv8.5-A.

Pseudocode Operation

SpeculationBarrier(); // Physical speculation barrier; execution continues normally

Example

PSSBB

Encoding

Binary Layout

11010101000000110011

0100

11111

Format System Hint

Opcode 0xD503349F

Extension Base (v8.5)

Operands

Reference (Arm A64 ISA)

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xD503349F	PSSBB		A64		11010101000000110011 \| 0100 \| 1 \| 00 \| 11111

Description

Physical Speculative Store Bypass Barrier is a memory barrier that prevents speculative loads from bypassing earlier stores to the same physical address under certain conditions. For more information and details of the semantics, see Physical Speculative Store Bypass Barrier (PSSBB).