some question about arch/x86/kernel/head_64.S

[xiaoqiang zhao]

Hello:

After kernel is decompressed, the kernel will execute startup_64 and
the first two instructions are:

    leaq    _text(%rip), %rbp
    subq    $_text - __START_KERNEL_map, %rbp

I tried to understand them but can not figure out what rbp contains
after this two instructions. Anybody give me a clear explanation?

Thanks a lot!