[U-Boot-Users] why jump at absolute address in start.S

I'm reading cpu/mpc8xx/start.S and found the following:

/* * Calculate absolute address in FLASH and jump there */

lis r3, CFG_MONITOR_BASE@h ori r3, r3, CFG_MONITOR_BASE@l addi r3, r3, in_flash - _start + EXC_OFF_SYS_RESET mtlr r3 blr

Why do we need to calculate the absolutely address? Why should we do it here, instead of everywhere?

Thanks. Laudney