Plan 9: Quick Boot with UEFI

 UEFI (Unified Extensible Firmware Interface) provides a quick way to set up a Plan 9 terminal on modern hardware. EFI System Partition (ESP) is a FAT32 partition. You should be able to modify it in most of the operating systems.  

Run mk in \sys\src\boot\efi. aux/aout2efi converts an a.out file to an EFI executable. Copy over the files bootx64.efi, 9pc64, plan9.ini (for x86_64 hardware) to \EFI\plan9\ directory in the ESP. If you want it be the default OS, you can create a symlink \EFI\boot to \EFI\plan9. Remember to include the full path to the kernel in plan9.ini.

bootfile=\EFI\plan9\9pc64 
   

When bootx64.efi fails to find the bootfile, you can provide the arguments at > prompt followed by a boot command.

You can use EFI shell or efibootmgr on Linux to modify the EFI entries that are displayed during boot.

 

Test in QEMU

Before running on actual hardware, it might help to get familiar with the process in a virtual environment.
sudo apt-get install qemu-system ovmf

Copy all the files mentioned above to a root dir maintaining the directory structure. Also copy OVMF.fd to current dir.
cp /usr/share/qemu/OVMF.fd .

Then run QEMU using the following:
qemu-system-x86_64 -drive if=pflash,format=raw,file=OVMF.fd -drive format=raw,file=fat:rw:root

 

Programming

Print a CHAR16 string txt:
eficall(ST->ConOut->OutputString, ST->ConOut, txt);   
 

Image file path:

typedef struct {
  void *ConvertDeviceNodeToText;
  void *ConvertDevicePathToText;
} EFI_DEVICE_PATH_TO_TEXT_PROTOCOL;

static EFI_GUID EFI_DEVICE_PATH_TO_TEXT_PROTOCOL_GUID = {
  0x8b843e20,0x8132,0x4852,
  {0x90,0xcc,0x55,0x1a,0x4e,0x4a,0x7f,0x1c}
};


EFI_DEVICE_PATH_TO_TEXT_PROTOCOL *dpt;
CHAR16 *txt;
eficall(ST->BootServices->LocateProtocol, &EFI_DEVICE_PATH_TO_TEXT_PROTOCOL_GUID, nil, &dpt);
txt = (CHAR16*) eficall(dpt->ConvertDevicePathToText, image->FilePath, 1, 1);
   

  

Lessons Learnt

  • Always backup ESP especially if you need Windows. It's almost impossible to get bootmgr.efi for Windows from external sources. (Boot manager: \EFI\Microsoft\Boot\bootmgfw.efi , OS loader: \windows\system32\windload.efi) 
  • Depending on your configuration in Linux, you might have a copy of the ESP at /boot/efi.

 

References


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