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SP_EL0, Stack Pointer (EL0)

The SP_EL0 characteristics are:

Purpose

Holds the stack pointer associated with EL0. At higher Exception levels, this is used as the current stack pointer when the value of SPSel.SP is 0.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

SP_EL0 is a 64-bit register.

Field descriptions

The SP_EL0 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
Stack pointer
Stack pointer
313029282726252423222120191817161514131211109876543210

Bits [63:0]

Stack pointer.

This field resets to an architecturally UNKNOWN value.

Accessing the SP_EL0

When the value of PSTATE.SP is 0, this register is accessible at all Exception levels as the current stack pointer.

Accesses to this register use the following encodings:

MRS <Xt>, SP_EL0

op0op1CRnCRmop2
0b110b0000b01000b00010b000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if PSTATE.SP == '0' then
        UNDEFINED;
    else
        return SP_EL0;
elsif PSTATE.EL == EL2 then
    if PSTATE.SP == '0' then
        UNDEFINED;
    else
        return SP_EL0;
elsif PSTATE.EL == EL3 then
    return SP_EL0;
              

MSR SP_EL0, <Xt>

op0op1CRnCRmop2
0b110b0000b01000b00010b000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if PSTATE.SP == '0' then
        UNDEFINED;
    else
        SP_EL0 = X[t];
elsif PSTATE.EL == EL2 then
    if PSTATE.SP == '0' then
        UNDEFINED;
    else
        SP_EL0 = X[t];
elsif PSTATE.EL == EL3 then
    SP_EL0 = X[t];
              


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