Hi list,

In the source code arch/x86/boot/compressed/head_64.S, it described

how compressed kernel is copied from the origin place to another pointed by rbx register.

But I'm confused about the copying code, why it needs to minus 8 from _bss when calculating

_bss original and new addresses.

This is the source code.

/*

 * Copy the compressed kernel to the end of our buffer

 * where decompression in place becomes safe.

 */

pushq %rsi

leaq (_bss-8)(%rip), %rsi

leaq (_bss-8)(%rbx), %rdi

movq $_bss /* - $startup_32 */, %rcx

shrq $3, %rcx

std

rep movsq

cld

popq %rsi

Thanks,

Larry