17.135 SWPAB, SWPALB, SWPB, SWPLB

Swap byte in memory.

Syntax

SWPAB Ws, Wt, [Xn|SP] ; Acquire general registers

SWPALB Ws, Wt, [Xn|SP] ; Acquire and release general registers

SWPB Ws, Wt, [Xn|SP] ; No memory ordering general registers

SWPLB Ws, Wt, [Xn|SP] ; Release general registers

Where:

Ws
Is the 32-bit name of the general-purpose register to be stored.
Wt
Is the 32-bit name of the general-purpose register to be loaded.
Xn|SP
Is the 64-bit name of the general-purpose base register or stack pointer.

Architectures supported

Supported in ARMv8.1 and later.

Usage

Swap byte in memory atomically loads an 8-bit byte from a memory location, and stores the value held in a register back to the same memory location. The value initially loaded from memory is returned in the destination register.

  • If the destination register is not WZR, SWPAB and SWPALB load from memory with acquire semantics.
  • SWPLB and SWPALB store to memory with release semantics.
  • SWPB has no memory ordering requirements.

For more information about memory ordering semantics see Load-Acquire, Store-Release in the ARM Architecture Reference Manual ARMv8, for ARMv8-A architecture profile.

For information about memory accesses see Load/Store addressing modes in the ARM Architecture Reference Manual ARMv8, for ARMv8-A architecture profile.

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