Re: A question about decompressing kernel on boot
Hi Hao Lee, Really appreciate your help. :-) Regards, Larry -- Original -- From: "haolee.swjtu"<haolee.sw...@gmail.com>; Date: Mon, Feb 26, 2018 00:17 AM To: ""<losemyhea...@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___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: A question about decompressing kernel on boot
leaq (_bss-8)(%rip), %rsi leaq (_bss-8)(%rbx), %rdi movq $_bss /* - $startup_32 */, %rcx shrq $3, %rcx std rep movsq cld The movsq instruction copys 8 bytes each time and for the first time it will copy [_bss-8, _bss) to the new location. If we don't minus 8, the data in [_bss, _bss+8) will also be copied on the first execution of movsq. Obviously, we don't want to copy the bss section. Regards, Hao Lee___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
A question about decompressing kernel on boot
Hi list, In the source code arch/x86/boot/compressed/head_64.S, it described how compressed kernel is copied from the origin place to another pointed by rbx register. But I'm confused about the copying code, why it needs to minus 8 from _bss when calculating _bss original and new addresses. This is the source code. /* * Copy the compressed kernel to the end of our buffer * where decompression in place becomes safe. */ pushq %rsi leaq(_bss-8)(%rip), %rsi leaq(_bss-8)(%rbx), %rdi movq$_bss /* - $startup_32 */, %rcx shrq$3, %rcx std rep movsq cld popq%rsi Thanks, Larry___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
