If you are building with the firmware use the DebugLib in the INF and DEBUG(); macros.

DEBUG((DEBUG_ERROR, “It works\n”));

Also by setting your Depex to TRUE you are basically asking to run before the console is available. If you want to depend on all UEFI Services being present don’t set a dependency expression. The Depex is for ordering the early drivers that don’t follow the UEFI Driver Model. So for example you have to configure your chipset, and SPI driver to get UEFI NVRAM working etc. 

Thanks,

Andrew Fish

On Nov 2, 2022, at 5:58 PM, Pedro Falcato <pedro.falcato@gmail.com> wrote:

Hi!

If I recall correctly, UEFI drivers are not guaranteed to have a valid ConOut and ConIn, and you're not supposed to use those. They are (always?) valid in UEFI apps.
Can you try to use DebugLib (don't forget to place DebugLib in LibraryClasses) and DEBUG((DEBUG_INFO, "Blah\n")); ? That should pretty much work. Note that OVMF will send those debug messages to a special device, so you can pass "-debugcon file:debug.log -global isa-debugcon.iobase=0x402" to QEMU to keep them. The rest of your procedure looks mostly OK as far as I can tell.

Crash theory: ConOut was garbage, so you tried to jump into a random address. Random address had random data/instructions in there, which caused you an int 6 -> Invalid opcode.

Thanks,
Pedro

On Wed, Nov 2, 2022 at 2:02 PM d.meneses via groups.io <d.meneses=softi9.pt@groups.io> wrote:
As detailed on this post on Super User, I am trying to add a DXE driver to an OVMF image I'm building with edk2. Nobody was able to help me there so I turn here for your help.
 
I haven't found any proper documentation on exactly what I'm trying to achieve so I am probably missing something.
 
So far what I have done is:
  • create the simplest DXE driver I managed
In folder MdeModulePkg/Application/Hello, I have:
Hello.c : 
include
 
...
 
while (1)
        SystemTable->ConOut->OutputString(SystemTable->ConOut,
                                          L"It works!\n");
return EFI_SUCCESS;

 
Hello.inf : 
[Defines]
  INF_VERSION                    = 0x00010005
  BASE_NAME                      = Hello
  FILE_GUID                      = ...
  MODULE_TYPE                    = DXE_DRIVER
  VERSION_STRING                 = 1.0
  ENTRY_POINT                    = UefiMain


[Sources]
  Hello.c

[Packages]
  MdePkg/MdePkg.dec
  MdeModulePkg/MdeModulePkg.dec

[LibraryClasses]
  UefiDriverEntryPoint
  UefiLib

[Depex]
    TRUE
  • Set OvmfPkg/OvmfPkgX64.dsc as my target platform with GCC5 as the toolchain
  • Add MdeModulePkg/Application/Hello/Hello.inf to the end of the component section (I have tried to add it after other certain drivers) in the .dsc file.
  • Add MdeModulePkg/Application/Hello/Hello.inf to the end of the [FV.DXEFV] section in OvmfPkgX64.fdf (I have also tried to add it after other certain drivers)
  • Run build
  • Run QEMU with the resulting OVMF image: qemu-system-x86_64 -d int -D log.txt  -bios OVMF.fd -net none -drive file=fat:rw:bootdrv,format=raw
  • QEMU hangs with message "Guest has not initialized display (yet)"
  • log.txt has one log: check_exception old: 0xffffffff new 0x6
 




--
Pedro Falcato