Returns from an exception. It restores the processor state based on SPSR_EL
n and branches to ELR_EL
n is the current exception level..
Exception Return using the ELR and SPSR for the current Exception level. When executed, the PE restores PSTATE from the SPSR, and branches to the address held in the ELR.
The PE checks the SPSR for the current Exception level for an illegal return event. See Illegal return events from AArch64 state in the ARMv8-A Architecture Reference Manual.
ERET is undefined at EL0.