[U-Boot-Users] what means this symbol "@"?

In u-boot/cpu/mpc8xx/start.S,I usually find this symbol "@",such as followed:

_start: lis r3, CFG_IMMR@h /* position IMMR */ mtspr 638, r3 li r21, BOOTFLAG_COLD /* Normal Power-On: Boot from FLASH */ b boot_cold

what does it means? Thank you!