Computers as Components, 2nd Edition

74 CHAPTER 2 Instruction Sets

to return. To properly return, we must save the PC value when the procedure/

function is called and, when the procedure is finished, set the PC to the address of

the instruction just after the call to the procedure. (You don’t want to endlessly

execute the procedure,after all.) The branch-and-link instruction is used in theARM

for procedure calls. For instance,

BL foo

will perform a branch and link to the code starting at location foo (using PC-relative

addressing,of course).The branch and link is much like a branch,except that before

branching it stores the current PC value in r14. Thus, to return from a procedure,

you