SPSel, Stack Pointer Select
The SPSel characteristics are:
Purpose
Allows the Stack Pointer to be selected between SP_EL0 and SP_ELx.
Configuration
Some or all RW fields of this register have defined reset values. These apply only if the PE resets into an Exception level that is using AArch64. Otherwise, RW fields in this register reset to architecturally UNKNOWN values.
Attributes
SPSel is a 64-bit register.
Field descriptions
The SPSel 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 |
| RES0 | |||||||||||||||||||||||||||||||
| RES0 | SP | ||||||||||||||||||||||||||||||
| 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 [63:1]
Reserved, RES0.
SP, bit [0]
Stack pointer to use. Possible values of this bit are:
| SP | Meaning |
|---|---|
| 0b0 |
Use SP_EL0 at all Exception levels. |
| 0b1 |
Use SP_ELx for Exception level ELx. |
This field resets to 1.
Accessing the SPSel
For details on the operation of the MSR (immediate) accessor, see MSR (immediate) in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.
Accesses to this register use the following encodings:
MRS <Xt>, SPSel
| op0 | op1 | CRn | CRm | op2 |
|---|---|---|---|---|
| 0b11 | 0b000 | 0b0100 | 0b0010 | 0b000 |
if PSTATE.EL == EL0 then
UNDEFINED;
elsif PSTATE.EL == EL1 then
return Zeros(63):PSTATE.SP;
elsif PSTATE.EL == EL2 then
return Zeros(63):PSTATE.SP;
elsif PSTATE.EL == EL3 then
return Zeros(63):PSTATE.SP;
MSR SPSel, <Xt>
| op0 | op1 | CRn | CRm | op2 |
|---|---|---|---|---|
| 0b11 | 0b000 | 0b0100 | 0b0010 | 0b000 |
if PSTATE.EL == EL0 then
UNDEFINED;
elsif PSTATE.EL == EL1 then
PSTATE.SP = X[t]<0>;
elsif PSTATE.EL == EL2 then
PSTATE.SP = X[t]<0>;
elsif PSTATE.EL == EL3 then
PSTATE.SP = X[t]<0>;
MSR SPSel, #<imm>
| op0 | op1 | CRn | op2 |
|---|---|---|---|
| 0b00 | 0b000 | 0b0100 | 0b101 |