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contradiction in boot/i386/pc/boot.S


From: Robert Millan
Subject: contradiction in boot/i386/pc/boot.S
Date: Tue, 8 Jan 2008 11:50:57 +0100
User-agent: Mutt/1.5.13 (2006-08-11)

boot/i386/pc/boot.S reads:

        /*
         * This is a workaround for buggy BIOSes which don't pass boot
         * drive correctly. If GRUB is installed into a HDD, check if
         * DL is masked correctly. If not, assume that the BIOS passed
         * a bogus value and set DL to 0x80, since this is the only
         * possible boot drive. If GRUB is installed into a floppy,
         * this does nothing (only jump).
         */
boot_drive_check:
        jmp     1f      /* grub-setup may overwrite this jump */
        testb   $0x80, %dl
        jnz     1f
        movb    $0x80, %dl
1:

However, if 0x80 is really "the only possible boot drive", that means the
test is pointless and can be replaced with:

boot_drive_check:
        jmp     1f      /* grub-setup may overwrite this jump */
        movb    $0x80, %dl
1:

So AFAICT either the comment or the code needs adjusting.

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What use is a phone call, if you are unable to speak?
(as seen on /.)




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