Re: PrePiLib's FwVol.c can't handle padding before volume header

[Michael Zimmermann <sigmaepsilon92@gmail.com>]

The layout is basically the same as in ArmVirtQemuKernel.fdf but I've
changed the size to 8MB and these are the usage stats:
FV Space Information
FVMAINDEVICE [99%Full] 57856 total, 57800 used, 56 free
FVMAINMSM8960 [99%Full] 222336 total, 222312 used, 24 free
FVMAIN_COMPACT [63%Full] 8380416 total, 5305944 used, 3074472 free
FVMAIN [99%Full] 17026304 total, 17026264 used, 40 free
FVMAINQCOM [99%Full] 37184 total, 37152 used, 32 free

and here's an uefitool report:
https://pastebin.com/pnHNSFz4
The padding in line 13 is the one causing trouble. The interesting
part is that it's not zero. it's value is '08 CD 03 01'.

PrePiLib fails in this line:
https://github.com/tianocore/edk2/blob/5a44a766b597e4c9960ac1936e6d18001c5e7ce2/EmbeddedPkg/Library/PrePiLib/FwVol.c#L682
The reason is simply that VolumeHandle is offset by 4 bytes.

On Sun, Dec 10, 2017 at 10:33 PM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
> On 10 December 2017 at 21:22, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>> cc BaseTools maintainers
>>
>> On 10 December 2017 at 20:58, Michael Zimmermann
>> <sigmaepsilon92@gmail.com> wrote:
>>> 'uefitool' shows me that there are 4 bytes of padding right before
>>> FVMAIN when adding large(20MB) uncompressed FV's.
>>>
>>> FwVol fails detecting that and complains about the signature not being correct.
>>>
>
> I missed the 'PrePiLib' in the subject, apologies.
>
> So could you elaborate please? What is the layout of the FV, and
> when/how does PrePiLib complain about it?