Support FVs that have the Extended header.

[GanShun]

I've seen firmware volumes with the extended header preset, and it turns out on the roms I'm looking at, the HeaderLength field doesn't include the size of the extended header. To get the correct start of data, the ExtHeaderOffset must be added to the ExtendedHeaderSize if it exists.

[hugelgupf]

shouldn't this be an issue on fiano?

[GanShun]

I'm fixing it on fiano. Linuxboot extract-fv doesn't support it yet either. I wanna make a note for it.

[osresearch]

It might work with extract-firmware -- the s2600wf uses them: https://github.com/linuxboot/linuxboot/blob/master/bin/extract-firmware#L166:

		if ($len == 0xFFFFFF)
		{
			# Version 2 header with extended length
			$len = EFI::read64($fv, $offset + 0x18);

			# If we have an all-0xFF length, which indicates
			# the start of free space
			return 1 if ~$len == 0;

			## Looks good, adjust the starting offset
			$data_offset += 0x8;
		}

However, adding 0x8 is probably not the right general pupose way to use the extended header.

More important is probably adding support for creating FV larger than 16 MB, which would require doing it the right way.

[GanShun]

Wait I think the code you're pointing to is about supporting FFSes with the extended length. I'm talking about the FirmwareVolume header that is itself extended and pointed to by the ExtHeaderOffset in the standard header.
For reference: UEFI PI Spec 3.2.1 Firmware Volume Header.

There is an "extended header" that is pointed to by the FV header. In those cases, in order to know where the files actually start in the FV, you need to parse the extended header to find its length and add to its offset.

[GanShun]

Specifically this line needs to be fixed:

linuxboot/bin/extract-firmware

Line 153 in f0ea0af

my $offset = EFI::read16($fv, 0x30);

since it's not a given that that's where the data of the FV starts.

[osresearch]

You're right, that code was for dealing with FFS larger than 16 MB.

The FV parsing code handles volumes larger than 16 MB since it does a read64 of the length:

linuxboot/bin/extract-firmware

Line 97 in f0ea0af

my $fv_length = EFI::read64($_, $offset + 0x20);

But it does not include anything ot process the extended headers (since none of the ones I had encountered yet used it). Do you have a ROM image that uses them that we can add as a test case?

[GanShun]

Unfortunately I don't have one that I can share. We might be able to tweak winterfell's dxe to produce one that uses the extended header.