Dear Maintainers and others,
the attached patch-file closes to my understanding
the urgent bug 345931. I write this very message in
respons to a question of Robert Millan last Monday.
The patch
boot_drive_correction.diff
is simply a beautyfied version of the one submitted
the first time.
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.
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.
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.
Regards
Mats Erik Andersson
[EMAIL PROTECTED]
# boot_drive_correction.diff
#
# Enables the workaround for the "boot drive flag" used in grub 0.94-0.96
# to coexist with the revised principle of grub 0.97. Thereby the present
# version of the grub-shell restores correctly from (hd?,?)/boot/grub/*
# for the full span of versions 0.94-0.97. This is extendible also to
# grub 0.92-0.93, by following my proposition in the last comment below.
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. */
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)
