Motivations behind this target
The Unified Extensible Firmware Interface (UEFI) now replaces BIOS in most current PCs.
Currently, there are two main options to develop UEFI applications :
- Tianocore : http://www.tianocore.org/ - gnu-efi : http://sourceforge.net/projects/gnu-efi/
Both solutions require a tedious setup process.
Thank to its internal linker, Freepascal can become the easiest option to develop UEFI applications, as no external tools would be required to start hacking.
UEFI applications are PE binaries like the Windows target, which FreePascal already supports. The only difference is the subsystem in the PE header.
Calling conventions under UEFI are identical to the ones under Windows on the same architecture, which Freepascal already supports, too.
My current patch against trunk is here : http://nan.tf/download/uefi_all_03_01_2016.diff.
It is not yet a clean patch : lots of debug output inside.
Affectation of string constant to string variable does not work. It is currently necessary to create strings through an array of WideChar.
var s : string; begin s := 'Hello world !'; end;
Maybe it is related to Position Independent Code generation in the case of PE executables ?
Any hints in this area are welcome ;-)
Testing UEFI applications with qemu
To avoid creating an image, i use FAT emulation to a local directory where my UEFI application is located :
qemu-system-i386-x86 -pflash /path/to/OVMF.fd -hda fat:local_directory -net none
"-net none" avoid net booting to save a few seconds in the boot process.
From UEFI shell, then write :
to switch to the directory where are located your application then you can launch it :
Some interesting development resources around UEFI :
- UEFI specifications : http://www.uefi.org/ - OS development under UEFI : http://wiki.osdev.org/UEFI - UEFI bootloaders : http://www.rodsbooks.com/efi-bootloaders/principles.html