Re: [edk2-devel] static data in dxe_runtime modules

["Roman Kagan" <rkagan@virtuozzo.com>]

On Wed, Aug 14, 2019 at 09:26:47AM -0700, Andrew Fish via Groups.Io wrote:
> Every runtime driver I've every seen usually works like this:
> 1) Loads as an EFI driver and uses EFI Boot Services in its constructor (gBS, gDS, AllocatePool(), etc.)
> 2) You use the EFI Boot Service to register the ExitBootServices Event. 
> 3) SetVirtualAddressMap event fires and converts all the pointers 
> 4) After all the ExitBootServices events have been processed the DXE Runtime driver re-relocates the Runtime Driver
> 5) The next code that runs is a call from the kernel virtual mapping, and the system is at runtime 
> 
> It is important to remember that when gRT->SetVirtualAddressMap() is
> called by the OS Loader (or early kernel) that gBS->ExitBootServices()
> has already been called. So by the time you get 3) almost all of EFI
> is gone. The only services that remain are gRT. Note you find the
> location of gRT by using the gST passed into the entry point of the
> driver. So here is lies the problem the entry point is passed a Handle
> (EFI Boot Services concept) and a pointer to gST (another boot
> services table). So you can't really reload a module and expect it to
> work. 

Indeed.  My hope was that the particular VariableRuntimeDxe module was
just a bunch of self-contained code that accesses all the data it needs
through the arguments it's passed.  Having now looked at the code, this
assumption is certainly wrong: the module depends on a lot of private
data that is initialized at boot services time.

Thanks and sorry for the noise,
Roman.