[U-Boot] get linker variable error.

hi there , I'm a newbie to U-boot, the following picture is the disassembly of u-boot: I'm using u-boot 2013.01 . when clear bss section, the __bss_start and __bss_end__ was wrong, it was zero. but in the map file , the __bss_start & __bss_end__ was right . could you help me ? Thanks.

-- Aking Best regards