stitch626 / uefiseven

An EFI loader that emulates int10h interrupts needed for booting Windows 7 under UEFI Class 3 systems.

UefiSeven

Summary

UefiSeven is an efi module that enables Windows 7 to boot under UEFI Class 3 systems.

Windows 7 does not fully support UEFI and relies on legacy BIOS interrupt 10 (Int10h) during initial graphics initialization. On computers without proper legacy support Windows 7 might freeze on 'Starting Windows' screen or fail with error code 0xc000000d. Some motherboards have 'CSM' or 'legacy' boot options to fix this problem but it is getting increasingly rare as Intel decided to get rid of legacy BIOS support by 2020, and the option is virtually non-existent on consumer mobile devices. UefiSeven installs a minimal Int10h handler in the memory before Windows boots up so that the boot process do not fail because of the missing interrupt.

UefiSeven also contains a hack to enable screen output on hardwares that do not natively support 1024x768 as is needed by Windows Installer. Int10h handler comes with a macro, when enabled before compiling, that will enable serial console output which can be used to debug the handler itself.

Usage instructions

1. Prepare Windows 7 installation USB Drive
2. Rename bootx64.efi at (UsbDrive)\EFI\Boot\ to bootx64.original.efi
3. Unpack bootx64.efi from UefiSeven archive and copy it to (UsbDrive)\EFI\Boot\
4. (Optional) Copy UefiSeven.verbose to the same directory to enable verbose mode
5. Finish initial installation and wait for reboot prompt
6. Power off computer
7. Rename bootmgfw.efi at (HDD)\EFI\Microsoft\Boot\ to bootmgfw.original.efi
8. Copy UefiSeven bootx64.efi to (HDD)\EFI\Microsoft\Boot\bootmgfw.efi using EFI shell
9. (Optional) Copy UefiSeven.skiperrors to the same directory to ignore any warning prompts.

Settings

Currently settings can be applied by creating empty files of specific name in the directory containing the main efi file.

• UefiSeven.verbose : Enables verbose mode
• UefiSeven.skiperrors : Skips any warning/error prompts
• UefiSeven.force_fakevesa : Overwrites Int10h handler with fakevesa even when the native handler is present

Build instructions

git clone https://git.mananet.net/manatails/uefiseven
cd UefiSeven
source ./edksetup.sh
make -C BaseTools/
./MdeModulePkg/Application/UefiSeven/Int10hHandler.sh ; Regenerate Int10h assembly. Optional
build -a X64 -t GCC49 -b RELEASE -p MdeModulePkg/MdeModulePkg.dsc

Credits

• Original VgaShim project
• OVMF project
• EDK II project