Replace POSIX-UEFI with Nyu-EFI

[mintsuki]

This PR replaces POSIX-UEFI with Nyu-EFI. The build system code is taken from the Nyu-EFI template.

This is a work in progress as it currently GPFs when executing some CALL16 and the GitHub Actions part hasn't been modified. If this PR is of interest I will continue working on it.

Nyu-EFI is a much simpler solution for making EFI applications. It only provides headers, no library, except a small relocation stub that allows ELF toolchains (both GCC and LLVM) to be used for building and examining the executable, prior to the conversion to PE.

[mintsuki]

I got it working!

[FlyGoat]

Please go ahead! I was a little bit concerned about POSIX-UEFI's ia32 compatibility and it seems like Nyu-EFI is doing better in this perspective.

[FlyGoat]

I just pushed some of my local work, please rebase.

[mintsuki]

Doing so as we speak :)

[mintsuki]

Done.

[mintsuki]

I believe everything should be fine now.

[FlyGoat]

Thanks for your work!

I have a couple of nits like BS/ST declaration should be in csmwrap.h and so on, do you mind to clean them up?

Also is it possible to use git submodule to manage dependency instead of custom scripts? I found that's much easier for me.

For libc functions my personal perference would be pull in https://github.com/picolibc/picolibc but I'm happy leave it as is given that we are not using much functions.

[mintsuki]

No problem!

The BS/ST variables are declared in csmwrap.h as externs, but they are defined in csmwrap.c as they need to be stored somewhere. Having variable definitions in a header is bad practice, and it wouldn't even work properly without -fcommon anymore.

Sure, I will convert to submodules if you prefer that.

Yeah, I agree that given we only use 5 libc functions, it's better to not pull in too many unnecessary foreign dependencies.

Furthermore, I forgot to clean up a bit the code to exit boot services in order to add all workarounds needed for real machines to work properly. This was a quick PoC that would work in QEMU with OVMF.

[FlyGoat]

cc -g -O2 -pipe -Wall -Wextra -std=gnu11 -nostdinc -ffreestanding -fno-stack-protector -fno-stack-check -fshort-wchar -fPIE -ffunction-sections -fdata-sections -m64 -march=x86-64 -mno-80387 -mno-mmx -mno-sse -mno-sse2 -mno-red-zone -I src -I nyu-efi/inc -isystem freestnd-c-hdrs  -MMD -MP -c src/printf.c -o obj-x86_64/printf.c.o
src/printf.c:10:10: fatal error: nanoprintf.h: No such file or directory
   10 | #include <nanoprintf.h>
      |          ^~~~~~~~~~~~~~
compilation terminated.

CI seems to be failing.

[mintsuki]

Fixed.

[FlyGoat]

Seems like cbvga stopped to work.
I'll investigate.

[FlyGoat]

I'll merge atm and try to debug further as we are not going to make a release any time soon.