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
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