Hints where I could find the spec of the EFI vars on-disk binary file format?

[akavel]

I'd like to try and build a minimal EFI vars file with just a single variable set (specifically, to set gEfiMdePkgTokenSpaceGuid.PcdPlatformBootTimeOut|L"Timeout"|gEfiGlobalVariableGuid|0x0|5=0), for use in QEMU. I tried to find out the format of the file somewhere, but for now I failed to do so. Per the UEFI spec, IIUC this format seems implementation-specific? (Unfortunately, it seems I won't be able to just easily build patched edk2 as I'm on macOS on aarch64, and AFAIU it doesn't compile here at the moment.)

By any chance, could you help me understand whether/how I could try to generate a small EFI vars file? is the format very complex, or rather simple? where could I find some kind of a spec of its format?