> On Jun 16, 2022, at 7:20 AM, Ayush Singh <ayushdevel1...@gmail.com> wrote:
>
> Hello everyone, I wanted to ask if the edk2 build system also links to
> crt0-efi, like GNU-EFI?
>
> If yes, I would also like to see how that is actually implemented. If
> not, how does edk2 support custom entry functions? It is possible with
> llvm backend but I am not sure how it is done in GCC and am curious,
>
The general answer for edk2 is and library that a `CONSTRUCTOR =` statement in
its INF that lib constructor will get called when the Driver/App is started.
The actually entry point for a Driver/App is _ModuleEntryPoint(). The typical
way it is done is this is implemented in a phase specific library[1]. This
phase specific basically calls 3 C functions that got generated by the build:
ProcessLibraryConstructorList(), ProcessModuleEntryPointList(), and
ProcessLibraryDestructorList(). The library constructor/destructors functions
call the lib constructor/destructors function based in the sequence of the
dependency graph of the libraries that get pulled in.
> Currently, rust does not support the custom implementation of
> `lang_start` (which is started by crt0 in most platforms), so I was
> trying to find ways to be able to use custom crt0 which sets up
> `SystemTable` and `SystemHandler` and start the `lang_start` from it.
> This way, the user will be able to call the normal `main` function
> rather than using the `no_main` feature.
>
If you look in the build output of an edk2 C driver/app you will see an
AutoGen.h and AutoGen.c file. This was the C code the build system
autogenerated to glue everything together. It manages gluing in the libs,
abstracting the PCD implementation, and adding C constants for EFI_GUID values.
Sorry I don’t know Rust yet. Is it possible to call C, EFIABI, from Rust code?
If yes maybe what you need is a Rust ModuleEntryPoint that can call the C
library constructor and a C EFIABI entry function for your Rust. I’m not sure
how you manage dealing with C includes in Rust? With C++ you can just decorate
them.
I guess the other 100% Rust option is to know the INF is building Rust (INF has
Code.rs files) and build Rust (or Rust compatible) AutoGen
> My blog post [1] shows how we currently use the `efi_main` function.
>
> Yours sincerely,
> Ayush Singh
>
> [1]: (https://www.programmershideaway.xyz/post5/)
>
>
[1]
https://github.com/tianocore/edk2/blob/master/MdePkg/Library/UefiApplicationEntryPoint/ApplicationEntryPoint.c
Thanks,
Andrew Fish
>
>
>
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