Messages in this thread | | | Date | Tue, 20 Nov 2012 13:12:26 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH v2 03/13] x86: Add macro for 64bit entry startup_64 |
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On 11/20/2012 12:55 PM, Yinghai Lu wrote: > On Tue, Nov 20, 2012 at 12:44 PM, H. Peter Anvin <hpa@zytor.com> wrote: >> I don't see any point in three flags here. Let's stick to one flag; then it fits in the existing boot_flags field. > > the magic AA55 > > boot/header.S:boot_flag: .word 0xAA55 > > if change that to other value, would it break existing boot loader? > aka old boot loader could boot the new bzImage anymore. >
Sorry, I meant loadflags.
This is a read flag and so should be low, bit 1 presumably.
On the other hand, the read flags in loadflags has not been modified for a very long time, and there is a serious risk that some broken bootloader might be doing a full byte comparison.
relocatable_kernel really should have been a flag, but it is now defined as a comparison with zero. As such, and in an effort to minimize the growth of struct setup_header (it is limited to little over 128 bytes long) I suggest we redefine the 16-byte field at offset 0x236 as a new flags field. We still only need one flag, though.
Backwards compatibility is so much fun.
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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