SETP, SETM, SETE

Memory Set. These instructions perform a memory set using the value in the bottom byte of the source register. The prologue, main, and epilogue instructions are expected to be run in succession and to appear consecutively in memory: SETP, then SETM, and then SETE.

SETP performs some preconditioning of the arguments suitable for using the SETM instruction, and performs an IMPLEMENTATION DEFINED amount of the memory set. SETM performs an IMPLEMENTATION DEFINED amount of the memory set. SETE performs the last part of the memory set.

Note

The inclusion of IMPLEMENTATION DEFINED amounts of memory set allows some optimization of the size that can be performed.

The architecture supports two algorithms for the memory set: option A and option B. Which algorithm is used is IMPLEMENTATION DEFINED.

Note

Portable software should not assume that the choice of algorithm is constant.

After execution of SETP, option A (which results in encoding PSTATE.C = 0):

• If Xn<63> == 1, the set size is saturated to 0x7FFFFFFFFFFFFFFF.
• Xd holds the original Xd + saturated Xn.
• Xn holds -1* saturated Xn + an IMPLEMENTATION DEFINED number of bytes set.
• PSTATE.{N,Z,V} are set to {0,0,0}.

After execution of SETP, option B (which results in encoding PSTATE.C = 1):

• If Xn<63> == 1, the copy size is saturated to 0x7FFFFFFFFFFFFFFF.
• Xd holds the original Xd + an IMPLEMENTATION DEFINED number of bytes set.
• Xn holds the saturated Xn - an IMPLEMENTATION DEFINED number of bytes set.
• PSTATE.{N,Z,V} are set to {0,0,0}.

For SETM, option A (encoded by PSTATE.C = 0), the format of the arguments is:

• Xn is treated as a signed 64-bit number.
• Xn holds -1* number of bytes remaining to be set in the memory set in total.
• Xd holds the lowest address that the set is made to -Xn.
• At the end of the instruction, the value of Xn is written back with -1* the number of bytes remaining to be set in the memory set in total.

For SETM, option B (encoded by PSTATE.C = 1), the format of the arguments is:

• Xn holds the number of bytes remaining to be set in the memory set in total.
• Xd holds the lowest address that the set is made to.
• At the end of the instruction:
  • the value of Xn is written back with the number of bytes remaining to be set in the memory set in total.
  • the value of Xd is written back with the lowest address that has not been set.

For SETE, option A (encoded by PSTATE.C = 0), the format of the arguments is:

• Xn is treated as a signed 64-bit number.
• Xn holds -1* the number of bytes remaining to be set in the memory set in total.
• Xd holds the lowest address that the set is made to -Xn.
• At the end of the instruction, the value of Xn is written back with 0.

For SETE, option B (encoded by PSTATE.C = 1), the format of the arguments is:

• Xn holds the number of bytes remaining to be set in the memory set in total.
• Xd holds the lowest address that the set is made to.
• At the end of the instruction:
  • the value of Xn is written back with 0.
  • the value of Xd is written back with the lowest address that has not been set.

Integer
(FEAT_MOPS)

if !IsFeatureImplemented(FEAT_MOPS) || sz != '00' then UNDEFINED;

SETParams memset;
memset.d = UInt(Rd);
memset.s = UInt(Rs);
memset.n = UInt(Rn);
bits(2) options = op2<1:0>;
boolean nontemporal = options<1> == '1';

case op2<3:2> of
    when '00' memset.stage = MOPSStage_Prologue;
    when '01' memset.stage = MOPSStage_Main;
    when '10' memset.stage = MOPSStage_Epilogue;
    otherwise UNDEFINED;

CheckMOPSEnabled();

if (memset.s == memset.n || memset.s == memset.d || memset.n == memset.d || memset.d == 31 || memset.n == 31) then
    Constraint c = ConstrainUnpredictable(Unpredictable_MOPSOVERLAP31);
    assert c IN {Constraint_UNDEF, Constraint_NOP};
    case c of
        when Constraint_UNDEF UNDEFINED;
        when Constraint_NOP   EndOfInstruction();

Assembler Symbols

bits(8) data = X[memset.s, 8];
integer B;

memset.is_setg = FALSE;
memset.nzcv = PSTATE.<N,Z,C,V>;
memset.toaddress = X[memset.d, 64];
if memset.stage == MOPSStage_Prologue then
    memset.setsize = UInt(X[memset.n, 64]);
else
    memset.setsize = SInt(X[memset.n, 64]);
memset.implements_option_a = SETOptionA();

boolean privileged = if options<0> == '1' then AArch64.IsUnprivAccessPriv() else PSTATE.EL != EL0;

AccessDescriptor accdesc = CreateAccDescMOPS(MemOp_STORE, privileged, nontemporal);

if memset.stage == MOPSStage_Prologue then
    if memset.setsize > 0x7FFFFFFFFFFFFFFF then
        memset.setsize = 0x7FFFFFFFFFFFFFFF;

    if memset.implements_option_a then
        memset.nzcv = '0000';
        memset.toaddress = memset.toaddress + memset.setsize;
        memset.setsize = 0 - memset.setsize;
    else
        memset.nzcv = '0010';

memset.stagesetsize = MemSetStageSize(memset);

if memset.stage != MOPSStage_Prologue then
    CheckMemSetParams(memset, options);

AddressDescriptor memaddrdesc;
PhysMemRetStatus memstatus;
integer memory_set;
boolean fault = FALSE;

if memset.implements_option_a then
    while memset.stagesetsize < 0 && !fault do
        // IMP DEF selection of the block size that is worked on. While many
        // implementations might make this constant, that is not assumed.
        B = SETSizeChoice(memset, 1);
        assert B <= -1 * memset.stagesetsize;

        (memory_set, memaddrdesc, memstatus) = MemSetBytes(memset.toaddress + memset.setsize, data, B, accdesc);

        if memory_set != B then
            fault = TRUE;
        else
            memset.setsize = memset.setsize + B;
            memset.stagesetsize = memset.stagesetsize + B;

else
    while memset.stagesetsize > 0 && !fault do
        // IMP DEF selection of the block size that is worked on. While many
        // implementations might make this constant, that is not assumed.
        B = SETSizeChoice(memset, 1);
        assert B <= memset.stagesetsize;

        (memory_set, memaddrdesc, memstatus) = MemSetBytes(memset.toaddress, data, B, accdesc);

        if memory_set != B then
            fault = TRUE;
        else
            memset.toaddress = memset.toaddress + B;
            memset.setsize = memset.setsize - B;
            memset.stagesetsize = memset.stagesetsize - B;

UpdateSetRegisters(memset, fault, memory_set);

if fault then
    if IsFault(memaddrdesc) then
        AArch64.Abort(memaddrdesc.vaddress, memaddrdesc.fault);
    else
        boolean iswrite = TRUE;
        HandleExternalAbort(memstatus, iswrite, memaddrdesc, B, accdesc);

if memset.stage == MOPSStage_Prologue then
    PSTATE.<N,Z,C,V> = memset.nzcv;