Hi Hao Lee, Really appreciate your help. :-) Regards, Larry ------------------ Original ------------------ From: "haolee.swjtu"<haolee.swjtu@gmail.com>; Date: Mon, Feb 26, 2018 00:17 AM To: "落痕"<losemyheaven@foxmail.com>; Cc: "kernelnewbies"<kernelnewbies@kernelnewbies.org>; Subject: Re: A question about decompressing kernel on boot leaq (_bss-8)(%rip), %rsi leaq (_bss-8)(%rbx), %rdi movq $_bss /* - $startup_32 */, %rcx shrq $3, %rcx std rep movsq cld The movsq instruction copys 8 bytes each time and for the first time it will copy [_bss-8, _bss) to the new location. If we don't minus 8, the data in [_bss, _bss+8) will also be copied on the first execution of movsq. Obviously, we don't want to copy the bss section. Regards, Hao Lee