UEFI App Bare Bones: Difference between revisions

 

This tutorial uses the header files and GUID definitions from the [[GNU-EFI]] project, but does '''not''' use the gnu-efi build system, but rather the MinGW-w64 or LLVM/Clang toolchain.

 

== Prerequisites ==

To build the EFI filesystem image, developers can use [[MTools]] or [https://github.com/jncronin/mkgpt '''mkgpt'''] to create a hard disk image. To build a CD image, '''xorriso''' (in [[mkisofs]] emulation mode) will be needed. To run under an emulator, it is best to use '''qemu-system-x86_64''' coupled with the [http://tianocore.sourceforge.net/wiki/OVMF '''x64 OVMF firmware'''].

 

 

cd mkgpt

automake --add-missing

./configure

make

 

== Testing the emulator ==

Now is a good time to check the emulator is working successfully with the OVMF firmware.

 

 

== Preparing the files ==

 

Next, create a file with the following:

#include <efilib.h>

 

 

return Status;

 

=== gnu-efi/lib/data.c ===

 

To build, use the cross-compiler:

# compile: (flags before -o become CFLAGS in the Makefile)

x86_64-w64-mingw32-gcc -ffreestanding -Ipath/to/gnu-efi/inc -Ipath/to/gnu-efi/inc/x86_64 -Ipath/to/gnu-efi/inc/protocol -c -o hello.o hello.c

# link: (flags before -o become LDFLAGS in the Makefile)

x86_64-w64-mingw32-gcc -nostdlib -Wl,-dll -shared -Wl,--subsystem,10 -e efi_main -o BOOTX64.EFI hello.o data.o

Note here that '--subsystem 10' specifies an EFI application for ld.

 

The build sequence under LLVM/clang is essentially the same, although there is the advantage of having ''all'' targets installed by default:

 

CFLAGS='-target x86_64-unknown-windows

-ffreestanding

clang $CFLAGS -c -o data.o path/to/gnu-efi/lib/data.c

clang $LDFLAGS -o BOOTX64.EFI hello.o data.o

 

Passing '--target x86_64-unknown-windows' to clang tells it to compile for x86_64 "Windows". This is quite not the same as 64-bit UEFI PE yet, but as before the "freestanding" part makes it a good kernel image. An example of this toolchain is found in the [https://github.com/c-util/c-efi c-efi] project.

 

Next, create a FAT filesystem image.

dd if=/dev/zero of=fat.img bs=1k count=1440

mformat -i fat.img -f 1440 ::

mmd -i fat.img ::/EFI/BOOT

mcopy -i fat.img BOOTX64.EFI ::/EFI/BOOT

 

=== Running as a USB stick image ===

The FAT image can either be written directly to a USB stick and used in in a UEFI machine, or it can be run directly in QEMU:

 

 

=== Creating and running the HD image ===

The HD image is a disk image in the [[GPT]] format, with the FAT image specially identified as a 'EFI System Partition'.

 

 

=== Creating and running the CD image ===

The ISO image is a standard ISO9660 image which contains the FAT image as a file. A special El Torito option (-e) then points EFI aware systems to this image to be loaded. The CD image can either be burned to a CD and ran in a UEFI machine, or run directly in QEMU:

cp fat.img iso

xorriso -as mkisofs -R -f -e fat.img -no-emul-boot -o cdimage.iso iso

 

== What to do next? ==

* [[UEFI ISO Bare Bones]]

* [[GNU-EFI]]

 

[[Category:Bare bones tutorials]]