[edk2-devel] [RFC] Expose HII package list via C variables

Thu Aug 26 14:47:14 UTC 2021

Hey Mike,

Yes, I am aware. My goal for that would be to declare support as 
optional to support drivers up until UEFI vX (whatever would be the spec 
to endorse drivers to move away from the PE/COFF section model), much 
like EFI 1.10 backwards-compatibility worked with UEFI 2.x, and have 
some enabled-by-default FixedPcd for HII PE/COFF support. Project 
Amaranth at ISP RAS for example would disable support for this right 
away, as there is no urgent dependency on any external software to 
backwards-support. Production consumer platforms would drop support 
eventually in the far future, just like with all the EFI 1.10 specifics. 
Possibly a DEBUG_WARN could be issued whenever such a section is 
encountered, to help identify modules relying on this model.

Considering the nature of the usage right now, i.e. Shell manual 
queries, I sure hope there aren't actually any dependencies on this. The 
new PE/COFF loader is yet to undergo extensive real-world platform 
testing on full-UEFI scale (it is already used to load OS loaders on a 
wider scale, but not e.g. Option ROMs), and so are the UEFI spec changes 
that are to be proposed for hardening the parser, so I hope this can 
just be squeezed into both. If you can give a sort of general vote 
whether this change can be endorsed or not, ignoring any real-world 
dependencies for the moment, I will clean up the changes, integrate them 
into any upcoming PE/COFF loader testing, and provide findings whenever 
they arrive.

Best regards,
Marvin

On 26/08/2021 16:37, Michael D Kinney wrote:
> Marvin,
>
> One constraint in this discussion is that the HII content in
> a PE/COFF resource section is defined in the UEFI Specification,
> Which means UEFI Apps and UEFI Drivers from media and option ROMs
> that are not part of the system FW image are allowed to use this
> feature,  This means the system FW PE/COFF loader must support
> loading HII content from this PE/COFF resource section to be UEFI
> conformant.  So we cannot remove this feature from the PE/COFF
> loader without changes to the UEFI Specification.  Even if
> changes to the UEFI Specification we made, we would have to
> continue to support this feature for backward compatibility
> with existing UEFI Apps/Drivers that may be using this
> feature.
>
> Thanks,
>
> Mike
>
>> -----Original Message-----
>> From: devel at edk2.groups.io <devel at edk2.groups.io> On Behalf Of Marvin Häuser
>> Sent: Thursday, August 26, 2021 1:51 AM
>> To: devel at edk2.groups.io; Kinney, Michael D <michael.d.kinney at intel.com>
>> Cc: devel at edk2.groups.io; Andrew Fish <afish at apple.com>; leif at nuviainc.com; Ni, Ray <ray.ni at intel.com>; Gao, Zhichao
>> <zhichao.gao at intel.com>; Wang, Jian J <jian.j.wang at intel.com>; Wu, Hao A <hao.a.wu at intel.com>; Bi, Dandan
>> <dandan.bi at intel.com>; Dong, Eric <eric.dong at intel.com>; Bret Barkelew <Bret.Barkelew at microsoft.com>; Vitaly Cheptsov
>> <vit9696 at protonmail.com>
>> Subject: Re: [edk2-devel] [RFC] Expose HII package list via C variables
>>
>> Hey Mike,
>>
>> Thanks for your reply!
>>
>> Well, this switch is not well-documented. Looking now at both the
>> generation code and the emitted code, it does not generate a package
>> list like my code does, but separate data variables (strings and images)
>> that cannot easily be passed to HiiDatabase as-is. However apparently
>> there are drivers that use this functionality successfully by composing
>> the package list at runtime [1].
>>
>> Looking with this information now at the pattern of using HII C
>> variables (which I did not know existed before) vs the PE/COFF HII
>> section, most that use latter are Shell applications, which I guess
>> means the section has actually been introduced to resolve D.? There are
>> exceptions such as LogoDxe [2], which use the PE/COFF section while D.
>> is not a problem, hence I got confused, sorry. I think these modules
>> should be updated in any case. Do you agree?
>>
>> So, for modules that use C variables already, my patch would save some
>> runtime generation code and dynamic memory allocation for the HII
>> package list. This was not my goal (as I said, I didn't realise HII C
>> variables already were a thing in the first place), but the changes are
>> small enough that it might be worth considering anyway, in my opinion.
>> If a HII package list is generated for both Shell and non-Shell apps,
>> this also means code paths can be unified. For example, there could be a
>> library class with constructor and destructor to add/remove packages
>> from the HII database for all modules that use such, Shell or not. For
>> BaseTools it means that there is no real need for separate Python and C
>> paths as ideally they just generate the exact same data.
>>
>> Now to D., the only usage for this seems to be that Shell can locate the
>> help text in the executable without executing it, yet it is fully loaded
>> anyway [3]. To be honest, I find it hard to justify loading an
>> executable (PE/COFF loading, memory permission application, the full
>> process) to retrieve a help text and then unloading it again, especially
>> with the HII code being on a core dispatcher level. 1. to 7. still hold
>> true in my opinion. Was there any discussion I could read through why
>> Shell apps cannot simply support a "--help" or "-?" command and output
>> the string themselves? Pushing the burden to the Shell apps does
>> preserve the "drawback" that a full loading is required (which honestly
>> does not matter for a debugging application like Shell), however it does
>> relieve the burden of PE/COFF HII parsing from the core dispatcher
>> (which matters a lot in my opinion to keep the core simple). It would
>> simply be a normal Shell app execution as any other however. If someone
>> wants to avoid the PE/COFF burden altogether, they can still provide a
>> .man file.
>>
>> As for my points 6. and 7., maybe I should provide some context. Due to
>> many issues with TE files, platforms started abandoning them and
>> returned to PE/COFF Images. I think a big reason for this is that TE is
>> not really a sound and complete format, but a stripped version of
>> PE/COFF with none of the necessary fixups applied. I'm currently
>> sketching a possible alternative [4], and I would really like to not
>> having to specify a HII section type, while still preserving
>> compatibility with all of the UEFI Image types and use-cases [4].
>>
>> Thanks again!
>>
>> Best regards,
>> Marvin
>>
>>
>> [1]
>> https://github.com/tianocore/edk2/blob/7b4a99be8a39c12d3a7fc4b8db9f0eab4ac688d5/MdeModulePkg/Application/BootManagerMenuAp
>> p/BootManagerMenu.c#L929-L934
>>
>> [2]
>> https://github.com/tianocore/edk2/blob/7b4a99be8a39c12d3a7fc4b8db9f0eab4ac688d5/MdeModulePkg/Logo/LogoDxe.inf#L23
>>
>> [3]
>> https://github.com/tianocore/edk2/blob/7b4a99be8a39c12d3a7fc4b8db9f0eab4ac688d5/ShellPkg/Application/Shell/ShellManParser.
>> c#L646-L671
>>
>> [4]
>> https://github.com/mhaeuser/edk2/blob/ue_poc/MdePkg/Include/IndustryStandard/UeImage.h
>>
>> 26.08.2021 00:34:12 Michael D Kinney <michael.d.kinney at intel.com>:
>>
>>> Hi Marvin,
>>>
>>> I think this feature is already there and supported.
>>>
>>> HII can either be in a global variable or in a PE/COFF resource section.
>>> The default is a global variable because HII was implemented before the
>>> PE/COFF resource section feature was added to the UEFI Specification.
>>>
>>> There is an INF [Defines] section statement to enable the PE/COFF
>>> section. See UefiHiiResource in the following link.
>>>
>>> https://tianocore-docs.github.io/edk2-InfSpecification/draft/3_edk_ii_inf_file_format/34_[defines]_section.html#34-
>> defines-section
>>> How is your proposal different than this existing capability?
>>>
>>> Thanks,
>>>
>>> Mike
>>>
>>>> -----Original Message-----
>>>> From: devel at edk2.groups.io <devel at edk2.groups.io> On Behalf Of Marvin Häuser
>>>> Sent: Wednesday, August 25, 2021 2:21 PM
>>>> To: devel at edk2.groups.io
>>>> Cc: Andrew Fish <afish at apple.com>; leif at nuviainc.com; Kinney, Michael D <michael.d.kinney at intel.com>; Ni, Ray
>>>> <ray.ni at intel.com>; Gao, Zhichao <zhichao.gao at intel.com>; Wang, Jian J <jian.j.wang at intel.com>; Wu, Hao A
>>>> <hao.a.wu at intel.com>; Bi, Dandan <dandan.bi at intel.com>; Dong, Eric <eric.dong at intel.com>; Bret Barkelew
>>>> <Bret.Barkelew at microsoft.com>; Vitaly Cheptsov <vit9696 at protonmail.com>
>>>> Subject: [edk2-devel] [RFC] Expose HII package list via C variables
>>>>
>>>> Good day everyone,
>>>>
>>>> Currently, the HII package list is stored in a PE/COFF resource section
>>>> [1]. I propose to store it in a C variable (byte array with a pointer to
>>>> it and its size exposed) instead. DxeCore would have a guard to toggle
>>>> the deprecated support for the automatic protocol installation. This has
>>>> the following advantages:
>>>>
>>>> 1. Fixes BZ (incl. future toolchains):
>>>> https://bugzilla.tianocore.org/show_bug.cgi?id=557
>>>> 2. Universal method across all toolchains and output file formats
>>>> 3. Saves error-prone parsing work
>>>> 4. Saves protocol install/locate work, the data is available right away
>>>> 5. The omission of a dedicated section can save space
>>>> 6. Terse file formats can support this and remain terse :)
>>>> 7. Removes a dependency on the PE/COFF format specifically
>>>>
>>>> A *very rough* PoC diff can be found here:
>>>> https://github.com/mhaeuser/edk2/compare/master...wip_hii_cvar
>>>> If the feedback is positive, I will clean it up of course. OVMF boots
>>>> with everything working fine.
>>>>
>>>> I'd explicitly like feedback on the following:
>>>> A. Is this an acceptable solution to BZ 557 (Andrew?)?
>>>> B. Is this an acceptable solution for the "HII workflow" (MdeModule
>>>> maintainers?)?
>>>> C. Is it acceptable to make support UEFI-side support for the old
>>>> mechanism optional (Stewards?)?
>>>> D. Can an acceptable alternative be found for the removed ShellPkg code
>>>> (Shell maintainers?)?
>>>>
>>>> As you can see the BaseTools part also is rough, but that is more a
>>>> question of "how" rather than "whether", so I'll postpone asking about it.
>>>>
>>>> Thanks for your time and feedback!
>>>>
>>>> Best regards,
>>>> Marvin
>>>>
>>>>
>>>> [1] "Once the image is loaded, LoadImage() installs
>>>> EFI_HII_PACKAGE_LIST_PROTOCOL on the handle if
>>>> the image contains a custom PE/COFF resource with the type 'HII'."
>>>> - UEFI 2.9, 7.4, "EFI_BOOT_SERVICES.LoadImage()"
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>
>
> 
>
>

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