UEFI: Difference between revisions

Legacy bootloaders can be developed in any environment that can generate flat binary images: NASM, GCC, etc. UEFI applications can be developed in any language that can be compiled and linked into a [[PE]] executable file and supports the calling convention used to access functions established in memory by the UEFI firmware. In practice this means one of two development environments: Intel's TianoCore EDK2 or, GNU-EFI or POSIX-UEFI.

[[GNU-EFI]] is a set of libraries and headers for compiling UEFI applications with a system's native GCC (does not work with LLVM CLang). It can't be used to compile UEFI firmware. Since it's just a couple of libraries against which a UEFI application can be linked, it is much easier to use than TianoCore.

An easy way to compile EFI applications on Linux (or any other POSIX compatible system) is POSIX-UEFI. It does not only provide the well-known [[libc]]-like API for your EFI application, but also ships a Makefile that can detect and set up the toolchain for you. Works with both GNU gcc and LLVM CLang. Normally uses the host's compiler, but it is also capable of detecting the need for cross-compilation.

It has POSIX-ized typedefs (like ''uintn_t'' instead of ''UINTN''), and it does not need nor ship the standard EFI headers. But if you install those from EDK2 or GNU-EFI, you can safely include those as well, there will be no naming conflicts. Still, those interfaces are properly defined, and all fields have exactly the same name as in EDK2, so a big advantage over GNU-EFI that you can do

The traditional "Hello, world" UEFI program goes like this. Note that instead of ''char **argv'', it has ''wchar_t **argv''.

int main (int argc, wchar_tchar **argv)

printf(L"Hello, world!\n");