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SWP, SWPA, SWPAL, SWPL

Swap word or doubleword in memory atomically loads a 32-bit word or 64-bit doubleword 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 one of WZR or XZR, SWPA and SWPAL load from memory with acquire semantics.
  • SWPL and SWPAL store to memory with release semantics.
  • SWP has no memory ordering requirements.

For more information about memory ordering semantics see Load-Acquire, Store-Release.

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

Integer
(Armv8.1)

313029282726252423222120191817161514131211109876543210
1x111000AR1Rs100000RnRt
size

32-bit SWP (size == 10 && A == 0 && R == 0)

SWP <Ws>, <Wt>, [<Xn|SP>]

32-bit SWPA (size == 10 && A == 1 && R == 0)

SWPA <Ws>, <Wt>, [<Xn|SP>]

32-bit SWPAL (size == 10 && A == 1 && R == 1)

SWPAL <Ws>, <Wt>, [<Xn|SP>]

32-bit SWPL (size == 10 && A == 0 && R == 1)

SWPL <Ws>, <Wt>, [<Xn|SP>]

64-bit SWP (size == 11 && A == 0 && R == 0)

SWP <Xs>, <Xt>, [<Xn|SP>]

64-bit SWPA (size == 11 && A == 1 && R == 0)

SWPA <Xs>, <Xt>, [<Xn|SP>]

64-bit SWPAL (size == 11 && A == 1 && R == 1)

SWPAL <Xs>, <Xt>, [<Xn|SP>]

64-bit SWPL (size == 11 && A == 0 && R == 1)

SWPL <Xs>, <Xt>, [<Xn|SP>]

if !HaveAtomicExt() then UNDEFINED;

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

integer datasize = 8 << UInt(size);
integer regsize = if datasize == 64 then 64 else 32;
AccType ldacctype = if A == '1' && Rt != '11111' then AccType_ORDEREDATOMICRW else AccType_ATOMICRW;
AccType stacctype = if R == '1' then AccType_ORDEREDATOMICRW else AccType_ATOMICRW;
boolean tag_checked = n != 31;

Assembler Symbols

<Ws>

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

<Wt>

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

<Xs>

Is the 64-bit name of the general-purpose register to be stored, encoded in the "Rs" field.

<Xt>

Is the 64-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(datasize) data;

if HaveMTEExt() then
    SetNotTagCheckedInstruction(!tag_checked);

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

// All observers in the shareability domain observe the
// following load and store atomically.
data = Mem[address, datasize DIV 8, ldacctype];
Mem[address, datasize DIV 8, stacctype] = X[s];

X[t] = ZeroExtend(data, regsize);
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