Why this code run into infinite loop in ARM

Question

I am learning ARM assembly and compiled a code which simply ran a loop 5 times but when ran it goes to infinite loop

.global main
main:
push {ip.lr}
sub r1,r1,r         


        

Answer 1

printf call destroys your r1. Save your loop invariant in non-scratch register.

Answer 2

R1 gets trashed by the call to printf - use a non-volatile register instead or save/restore R1 around the call to printf.