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I have single drive hda; still EDD shows valid and the _same_ MBR signature
for all possible 16 drives:
{pts/0}% cat /sys/firmware/edd/*/mbr_*
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
0x7fca3a0a
other attributes are correctly present for the drive 0x80 only.
Not being expert in x86 assembly, but comparing main loops for signature and
other info:
signature:
int $0x13
sti # work around buggy BIOSes
popw %dx
popw %es
popw %bx
jc edd_mbr_sig_done # on failure, we're done.
extended EDD info:
edd_check_ext:
movb $CHECKEXTENSIONSPRESENT, %ah # Function 41
movw $EDDMAGIC1, %bx # magic
int $0x13 # make the call
jc edd_done # no more BIOS devices
Is it possible that carry flag is cleared between return from int 0x13 and
querying for it in the former case? This would perfectly explain that EDD
does not notice failure of reading sector and simply copies the same
signature from the very first drive.
- -andrey
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