Comment 32 for bug 277903

I'm attaching the diagnostic MBR so users can test whether their system is affected and, more importantly, report the actual values their PC's BIOS is using.

Installing it is the same process as the instructions above, but using "mbr-diag.bin.gz" and "mbr-diag.bin". The MBR will produce a *very* concise report (it can only have 440 bytes of code). It will *not* try to boot the active partition, only read its boot-sector.

Replace this diagnostic MBR with the one above for regular booting.

At boot-time it will test for two key presses:

1. Ctrl key = Force use of first hard-disk regardless of the BIOS drive number in register DL
2. Shift = Force use of CHS addressing method for read_sector even when LBA addressing is available

The output will look like this:

 L D80 C3FF H10 S3F P1 O00000020 MAA55 E00
 Description Codes:
   L | C LBA or CHS addressing mode
   D drive number BIOS-reported drive number
   C cylinders Geometry of drive according to BIOS
   H heads
   S sectors
   P partition active partition number (first partition flagged active). '?' if no active partition
   O offset absolute sector offset of active partition . '????????' if no active partition
   M magic magic bytes of active partition boot sector (sector <offset> as read by BIOS).
                                '????' if no active partition. Value is reset to 0xDEAD before the sector is read
                                to avoid inheriting the MBR magic on error
   E error error code returned by BIOS 'read sector' interrupt (0x02 or 0x42, int 0x13).
                                '??' if no active partition.