Mats Erik Andersson <[EMAIL PROTECTED]> writes:
> Yesterday I fetched from Debian Sid grub 0.97-16.1,
> built it and observed that, as expected according
> to #345931, it destroyed and made useless the MBR
> of my grub 0.95+cvs20040624-17sarge1. But by an
> application of my patch the altered version of
> of grub 0.97 (the patch does not touch any code
> alterations of debian) correctly is able to
> reactivate the the bootloader installed by grub 0.95.
I agree that compatibility here is important.
> Let me stress that the patch simply make shore that
> the relevant technique used for boot-drive-workaround
> of grub 0.94-0.97 is respected by grub 0.97. The
> revision 0.97 originally disregards this backwards
> compatibility. At the end of the patch, there is
> an indication of how compatability may be extended
> to versions 0.92-0.93, should the maintainers so
> desire.
Ok.
> Lastly, Robert Millan asks for relevance visavi
> Grub2. A quick check reveals that grub 1.94 does
> indeed utilize exactly the same workaround for
> harddisk booting as grub 0.97 does. The position
> at which this workaround is checked and applied is
>
> grub-1.94/util/i386/pc/grub-setup.c line 250.
>
> That position is the place to apply a patch with
> code accomodations to the new settings.
>
> HOWEVER, it is not clear to me if the Maintainers
> desire compatibility of Grub2 backwards to Grub
> Legacy in the sense that the former should be able to
> reactivate a bootloader installed by the latter.
> The maintainers need to decide on this on their own.
> I have not delved into the complete code of Grub2.
I think you should contact upstream and check if they wants to have
compatibility and then provide a patch to them.
Let's now review your current patch:
> diff -Naur grub-0.97-16.1.old/stage2/builtins.c
> grub-0.97-16.1/stage2/builtins.c
> --- grub-0.97-16.1.old/stage2/builtins.c 2006-09-27 22:48:46.068364160
> +0200
> +++ grub-0.97-16.1/stage2/builtins.c 2006-09-28 00:15:47.535580488 +0200
> @@ -2229,13 +2229,31 @@
> *((unsigned char *) (stage1_buffer + STAGE1_FORCE_LBA)) = is_force_lba;
>
> /* If DEST_DRIVE is a hard disk, enable the workaround, which is
> - for buggy BIOSes which don't pass boot drive correctly. Instead,
> - they pass 0x00 or 0x01 even when booted from 0x80. */
> + * for buggy BIOSes which don't pass boot drive correctly. Instead,
> + * they pass 0x00 or 0x01 even when booted from 0x80. */
I agree that your proposed style is better but we would like to reduce
code divergence so please, revert this one since this is just code
style fixing.
> if (dest_drive & BIOS_FLAG_FIXED_DISK)
> - /* Replace the jmp (2 bytes) with double nop's. */
> - *((unsigned short *) (stage1_buffer + STAGE1_BOOT_DRIVE_CHECK))
> - = 0x9090;
> -
> + {
> + if ( *((unsigned char *) (stage1_buffer + STAGE1_BOOT_DRIVE_CHECK)) ==
> 0xeb )
> + /* For present version 0.97:
> + * Replace the jmp (2 bytes) with double nop's. */
> + *((unsigned short *) (stage1_buffer + STAGE1_BOOT_DRIVE_CHECK))
> + = 0x9090;
> + else if ( *((unsigned char *) (stage1_buffer + STAGE1_BOOT_DRIVE_CHECK))
> == 0x80 )
> + {
> + /* For previous versions 0.94-96:
> + * Set the "boot drive mask". This is the old workaround for buggy
> BIOSes
> + * which do not pass boot drive correctly.
> + * REM: the old STAGE1_BOOT_DRIVE_MASK equals
> STAGE1_BOOT_DRIVE_CHECK + 2. */
> + *((unsigned char *) (stage1_buffer + STAGE1_BOOT_DRIVE_CHECK + 2 ))
> + = (dest_drive & BIOS_FLAG_FIXED_DISK);
> + }
> + else
> + /* The boot sector is older than version 0.94.
> + * Changing 'goto fail' to a "nop" could even make 0.92 and 0.93
> + * acceptable for the purpose of rescuing their installations.
> */
> + goto fail;
> + }
> +
> /* Read the first sector of Stage 2. */
> disk_read_hook = disk_read_savesect_func;
> if (grub_read (stage2_first_buffer, SECTOR_SIZE) != SECTOR_SIZE)
The code is badly indented.
This code also looks great for upstream subimition. I would like if
you could send it to bug-grub@gnu.org and talk to them. If you can get
it there would be easier to us just grub a CVS snapshot for packaging
proposes.
After fixing the issues that I pointed out would be good to send it
upstream and check why _they_ broke the compatibility. Should exist a
reason for it.
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