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Data processing and other instructions 105
4.3.2 Accessing the PSTATE register
These two instructions allow the programmer to access the status bits of the CPSR and SPSR:
mrs Move Status to Register, and
msr Move Register to Status.
4.3.2.1 Syntax
mrs Xt, <field>
msr <field>, Xt
• The optional <fields> is any one of:
NZCV Condition Flags
DAIF Interrupt Bits
CurrentEL Current Exception Level
PAN Privileged Access Never (ARMv8.1 only)
UAO User Access Override (ARMv8.2-UAO only)
• The optional <cond> can be any of the codes from Table 3.2 specifying conditional exe-
cution.
4.3.2.2 Operations
Name Effect Description
mrs Xt ← PSTATE Move from Process State.
msr PSTATE ← Xt Move to Process State.
4.3.2.3 Examples
nzcv is the only PSTATE field guaranteed to be accessible at the lowest execution state, EL0,
which is unprivileged and where applications are intended to be run:
1 mrs x0, NZCV // Read the NZCV flags into r0
2 and x0, xzr, x0 // Clear the flags
3 msr NZCV, x0 // Write the flags back
4.3.3 Supervisor call
The following instruction allows a user program to perform a system call to request operating
system services:
