Which register does store cmp result in arm?

Question

I need to write a function that after work sets all registers except r0-r3 to their initial values. I use push and pop, but I can't find which register stores the value of CMP.

UPD. Thank you. It seems I am wrong. I had an assignment that had a hint: "Don't forget about callee-save registers", so it wasn't suggesting treating flags as callee saved)

Answer 1

cmp, like all ARM instructions with an s suffix like subs, set flags / condition codes. These condition codes live in a register called CPSR, the Current Program Status Register. Also https://en.wikipedia.org/wiki/ARM_architecture#Registers

In all standard function-calling conventions, flags / condition codes are call-clobbered. You don't need to save/restore the caller's CPSR. Just let it be call-clobbered, along with r0..3.

But if you did, see https://heyrick.eu/armwiki/The_Status_register for examples like

    MRS     R0, CPSR                ; Copy CPSR into R0

    ...
    MSR     CPSR, R0                ; Copy R0 into CPSR