Thanks very much for you hint! On 03/21/2018 05:57 PM, Thomas Gleixner wrote: > On Wed, 21 Mar 2018, Cao jin wrote: >> On 03/17/2018 06:01 PM, Cao jin wrote: >>> I find two small questions which confuse me a little. >>> >>> 1. >>> # Check signature at end of setup >>> cmpl $0x5a5aaa55, setup_sig >>> jne setup_bad >>> >>> setup_sig is defined in setup.ld, which points to the constant also >>> defined in setup.ld, so I don't figure out in which case they don't >>> equal and jump to setup_bad? > > That's a lame sanity check to make sure that nothing overwrote the loader. >
I see. >>> In my test, drop these 2 lines seems fine, system can boot without any >>> obvious error. > > Sure it does as long as you have no corruption. > >>> 2. >>> # Zero the bss >>> movw $__bss_start, %di >>> movw $_end+3, %cx >>> xorl %eax, %eax >>> subw %di, %cx >>> shrw $2, %cx >>> rep; stosl >>> >>> It is not a big deal, but I think replace "_end" with "__bss_end" make >>> more sense, and "_end" is already aligned to word length. And, there is >>> no other code use symbol "__bss_end". So I don't know is there any >>> reason to use "_end" here? > > It doesn't matter at all. But its also pointless to change it. > It does not matter and is pointless to change for kernel itself. It just may confuse a little for newbies who has interests. -- Sincerely, Cao jin
