FreeRTOS A53 port : ELx stack pointers in save and restore context

mathieu-42 wrote on Tuesday, November 29, 2016:


I am working with A53 port of FreeRTOS and I do not understand something in portASM.S file.

My program is running in EL3.

Why when the context is saved we switch stack pointer to EL0 stack pointer?

Then at the end of “portSAVE_CONTEXT” macro, we switch back to EL3 stack pointer.

.macro portSAVE_CONTEXT
	/* Switch to use the EL0 stack pointer. */


	/* Switch to use the ELx stack pointer. */


Same thing for .macro portRESTORE_CONTEXT.

If program is in EL3, why we do not use EL3 stack pointer?
Are there some security issues when we switch to EL0 stack pointer from EL3?

Best regards,


rtel wrote on Tuesday, November 29, 2016:

I will have to consult the hardware reference manual to recall…get
back to you.

mathieu-42 wrote on Wednesday, November 30, 2016:


rtel wrote on Sunday, December 11, 2016:

Looking at the code it looks like the EL0 stack pointer is used so stack
relative pushes/pops can be performed without corrupting the stack
pointer used by the interrupt handler itself.