GPT and UEFI booting

[tlaronde%polynum.com@localhost]

Hello,

On my workstation are several disks. The first one is legacy MBR
partitioned. A second one has been partioned using GPT.

The BIOS allows legacy+UEFI for booting. I boot generally from the first
disk, where NetBSD is installed and I want to test UEFI, using the
second one.

I have added, via gpt(8), and EFI system partition as the first index
in the GPT partitioned disk but when entering the UEFI shell (from the
BIOS), the partition is not recognized as a "simple filesystem" (a FAT)
and I can not list it or load UEFI programs from it.

During my experiments, I used gpt biosboot too, and the GPT PMBR has the
active flag set. I wonder if this is not the problem, the PMBR being in
fact more or less recognized as implying use "legacy" for it which could
explain why only four partitions are listed as blk devices in the UEFI
shell while there are nine of them in the GPT.

But there doesn't seem to be an option to unset the active flag on the
PMBR---and using fdisk(8) is _not_ the answer (I have tried it), since
if one uses it and rewrite the (P)MBR, the GPT is lost (`gpt restore'
doesn't even see the backup copy of the GPT stuff so, fortunately,
I had `gpt backup' before...).

Has anyone already faced such situation and does anyone know how to
remove the active flag from the GPT PMBR without breaking everything?

This flag is probably set in the file generated by `gpt backup' but
where?  In what looks like the MBR binary transcription (code)?

TIA,
-- 
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
                     http://www.kergis.com/
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