A question about decompressing kernel on boot

[落痕]

Hi Hao Lee,
Really appreciate your help.
:-)
Regards,
Larry






------------------ Original ------------------
From:  "haolee.swjtu"<haolee.swjtu at gmail.com>;
Date:  Mon, Feb 26, 2018 00:17 AM
To:  "落痕"<losemyheaven at foxmail.com>;
Cc:  "kernelnewbies"<kernelnewbies at 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
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