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# SP_EL1, Stack Pointer (EL1)

The SP_EL1 characteristics are:

## Purpose

Holds the stack pointer associated with EL1. When executing at EL1, the value of SPSel.SP determines the current stack pointer:

SPSel.SP | Current stack pointer
--- | ---
0b0 | SP_EL0
0b1 | SP_EL1

## Configuration

RW fields in this register reset to architecturally UNKNOWN values.

## Attributes

SP_EL1 is a 64-bit register.

## Field descriptions

The SP_EL1 bit assignments are:

63 | 62 | 61 | 60 | 59 | 58 | 57 | 56 | 55 | 54 | 53 | 52 | 51 | 50 | 49 | 48 | 47 | 46 | 45 | 44 | 43 | 42 | 41 | 40 | 39 | 38 | 37 | 36 | 35 | 34 | 33 | 32
Stack pointer
Stack pointer
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0

#### Bits [63:0]

Stack pointer.

This field resets to an architecturally UNKNOWN value.

## Accessing the SP_EL1

This accessibility information only applies to accesses using the MRS or MSR instructions.

When the value of SPSel.SP is 1, this register is also accessible at EL1 as the current stack pointer.

Note

When the value of SPSel.SP is 0, SP_EL0 is used as the current stack pointer at all Exception levels.

Accesses to this register use the following encodings:

#### MRS <Xt>, SP_EL1

op0 | op1 | CRn | CRm | op2
--- | --- | --- | --- | ---
0b11 | 0b100 | 0b0100 | 0b0001 | 0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then return NVMem[0x240]; elsif EL2Enabled() && HCR_EL2.NV == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then return SP_EL1; elsif PSTATE.EL == EL3 then return SP_EL1;

#### MSR SP_EL1, <Xt>

op0 | op1 | CRn | CRm | op2
--- | --- | --- | --- | ---
0b11 | 0b100 | 0b0100 | 0b0001 | 0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then NVMem[0x240] = X[t]; elsif EL2Enabled() && HCR_EL2.NV == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then SP_EL1 = X[t]; elsif PSTATE.EL == EL3 then SP_EL1 = X[t];

AArch32 Registers | AArch64 Registers | AArch32 Instructions | AArch64 Instructions | Index by Encoding | External Registers | External Registers by Offset | Registers by Functional Group | Proprietary Notice

15/04/2019 16:47; 8c23526ba8a13a72aada4137daf3e3977b49036e

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