[GSoC] Ways to make the x86_64 port work with UEFI

[Amaan Cheval]

On Sat, May 19, 2018 at 6:51 PM, Gedare Bloom <gedare at rtems.org> wrote:
> On Fri, May 18, 2018 at 5:53 PM, Joel Sherrill <joel at rtems.org> wrote:
>>
>>
>> On Fri, May 18, 2018 at 3:24 PM, Amaan Cheval <amaan.cheval at gmail.com>
>> wrote:
>>>
>>> Hi everyone!
>>>
>>> I've written a quick blog post summarizing the options I've considered
>>> to make the x86_64 port work with UEFI firmware - the primary winner
>>> seems to be in my eyes to use "gnu-efi" and to add support for the
>>> target "pei-x86-64" (aliased to "efi-app-x86_64") to
>>> "x86_64-rtems5-objcopy" in binutils. I've submitted a patch for this
>>> here[1].
>>
>>
>> That patch is quite simple so shouldn't be a problem if this is the
>> direction
>> that gets consensus.
>>>
>>>
>>> The blog post is here:
>>> https://blog.whatthedude.com/post/uefi-app-options/
>>>
>>> I'd appreciate all feedback (and please do let me know if I haven't
>>> provided enough context)!
>>>
>>> Specifically, some concerns I'd like to discuss are:
>>>
>>> - Does everyone agree with me on choosing gnu-efi + objcopy as our
>>> method of choice?
>>
>>
>> Does using gnu-efi add code that runs on the target? Can you point
>> us to the files, if so.

Sure. The files would run on the target, yes. These are the ones
listed here (as linked to in my blog post, perhaps without sufficient
emphasis):
https://wiki.osdev.org/UEFI#Developing_with_GNU-EFI

>>
>> Can you tell which approach FreeBSD takes?

FreeBSD takes the gnu-efi approach I see as the "winner" here (also a
link in the post):
https://github.com/freebsd/freebsd/blob/996b0b6d81cf31cd8d58af5d8b45f0b4945d960d/stand/efi/loader/Makefile#L98-L119

>>
>>>
>>> - How do we integrate gnu-efi into our build process? A part of the
>>> RSB, making sure the path to the libraries are in an exported
>>> variable? Or perhaps a part of the RTEMS kernel itself if the licenses
>>> are compatible (I don't see any on the project[2], only copyright
>>> notices within the source files of the release versions).
>>
>>
>> GNU-efi would be built like qemu or the device tree compiler would
>> be my guess and x86_64-rtems toolset might add that to the standard
>> set of tools. License on host tools being GPL isn't an issue.
>>
>
> It appears to be a standard 2-clause BSD released by Intel as
> specified in the README file of gnu-efi.
>
>>
>>>
>>> - Regardless of how we manage UEFI, do we require Multiboot support
>>> too? Multiboot drops us in a 32-bit protected mode environment,
>>> whereas 64-bit UEFI firmware will boot us into 64-bit long mode - this
>>> would mean the kernel would need to support separate code-paths for
>>> the 2 if we want to support both methods.
>>
>>
>> That's a good question. For GSoC, I think UEFI is fine and perhaps a ticket
>> under the general "modern PC support" ticket for multiboot support. Unless
>> that eliminates a LOT of PCs.
>>
>> I don't want you to spend all summer getting an image to boot both
>> ways. Personally, I want you to have a working BSP one way. :)
> +1
>

Noted, thanks!

>>>
>>>
>>> [1] https://www.sourceware.org/ml/binutils/2018-05/msg00197.html
>>> [2] https://sourceforge.net/projects/gnu-efi/
>>
>>
>> --joel
>>
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