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STREXD

Store Register Exclusive Doubleword derives an address from a base register value, stores a 64-bit doubleword from two registers to the derived address if the executing PE has exclusive access to the memory at that address, and returns a status value of 0 if the store was successful, or of 1 if no store was performed.

For more information about support for shared memory see Synchronization and semaphores. For information about memory accesses see Memory accesses.

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .

A1

Decode for this encoding

let t : integer = UInt(Rt); let t2 : integer = t + 1; let d : integer = UInt(Rd); let n : integer = UInt(Rn); if d == 15 || Rt[0] == '1' || t2 == 15 || n == 15 then UnpredictableProcedure(); end; if d == n || d == t || d == t2 then UnpredictableProcedure(); end;

CONSTRAINED UNPREDICTABLE behavior

If d == t, then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The store instruction executes but the value stored is unknown.

If d == n, then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The instruction performs the store to an UNKNOWN address.

If Rt<0> == '1', then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The instruction executes with the additional decode: Rt<0> = '0'.
• The instruction executes with the additional decode: t2 = t.
• The instruction executes as described, with no change to its behavior and no additional side effects.

If Rt == '1110', then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The instruction is handled as described in Using R15.

T1

Decode for this encoding

let d : integer = UInt(Rd); let t : integer = UInt(Rt); let t2 : integer = UInt(Rt2); let n : integer = UInt(Rn); if d == 15 || t == 15 || t2 == 15 || n == 15 then UnpredictableProcedure(); end; // Armv8-A removes UNPREDICTABLE for R13 if d == n || d == t || d == t2 then UnpredictableProcedure(); end;

CONSTRAINED UNPREDICTABLE behavior

If d == t, then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The store instruction executes but the value stored is unknown.

If d == n, then one of the following behaviors must occur:

• The instruction is undefined.
• The instruction executes as NOP.
• The instruction performs the store to an UNKNOWN address.

Assembler Symbols

Operational information

This instruction is a data-independent-time instruction as described in About the DIT bit.

2026-03_rel 2026-03-26 20:48:11

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