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LDAPRB

Load-Acquire RCpc Register Byte derives an address from a base register value, loads a byte from the derived address in memory, zero-extends it and writes it to a register.

The instruction has memory ordering semantics as described in Load-Acquire, Load-AcquirePC, and Store-Release, except that:

  • There is no ordering requirement, separate from the requirements of a Load-AcquirePC or a Store-Release, created by having a Store-Release followed by a Load-AcquirePC instruction.
  • The reading of a value written by a Store-Release by a Load-AcquirePC instruction by the same observer does not make the write of the Store-Release globally observed.

This difference in memory ordering is not described in the pseudocode.

For information about memory accesses, see Load/Store addressing modes.

Integer
(Armv8.3)

313029282726252423222120191817161514131211109876543210
00111000101(1)(1)(1)(1)(1)110000RnRt
sizeRs

Integer

LDAPRB <Wt>, [<Xn|SP> {,#0}]

integer n = UInt(Rn);
integer t = UInt(Rt);

boolean tag_checked = n != 31;

Assembler Symbols

<Wt>

Is the 32-bit name of the general-purpose register to be loaded, encoded in the "Rt" field.

<Xn|SP>

Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

Operation

bits(64) address;
bits(8) data;

if HaveMTEExt() then
    SetNotTagCheckedInstruction(!tag_checked);

if n == 31 then
    CheckSPAlignment();
    address = SP[];
else
    address = X[n];

data = Mem[address, 1, AccType_ORDERED];
X[t] = ZeroExtend(data, 32);

Operational information

If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.

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