GSoC'24: UEFI Graphics Output Protocol Support in Unikraft, Part III

This is the third post in a series of posts where I talk about my progress with the project.

Project Overview#

The widely available and standardized UEFI Graphics Output Protocol (GOP) interface is an excellent alternative to VGA or serial port consoles for printing logs to the screen.

This project aims to implement a UEFI GOP based console. For more information, check out Part I and Part II of this series.

Progress#

All the work referred to here can be found in this draft PR.

Arbitrary fonts#

The driver can now work with any arbitrary bitmap font! The bitmap font array, along with the width and height of each character can be defined in drivers/uktty/gop/font.c as follows:

__u8 char_width = 8;
__u8 char_height = 16;

__u8 font[256][16] = {
    {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}, // control char
    /* ... */
    {0x00, 0x00, 0x7C, 0xC6, 0xC6, 0x0C, 0x18, 0x18, 0x18, 0x00, 0x18, 0x18, 0x00, 0x00, 0x00, 0x00}, // question
    {0x00, 0x00, 0x00, 0x7C, 0xC6, 0xC6, 0xDE, 0xDE, 0xDE, 0xDC, 0xC0, 0x7C, 0x00, 0x00, 0x00, 0x00}, // at
    {0x00, 0x00, 0x10, 0x38, 0x6C, 0xC6, 0xC6, 0xFE, 0xC6, 0xC6, 0xC6, 0xC6, 0x00, 0x00, 0x00, 0x00}, // A
    {0x00, 0x00, 0xFC, 0x66, 0x66, 0x66, 0x7C, 0x66, 0x66, 0x66, 0x66, 0xFC, 0x00, 0x00, 0x00, 0x00}, // B
    /* ... */
    {0x00, 0x00, 0x00, 0x00, 0x10, 0x38, 0x6C, 0xC6, 0xC6, 0xC6, 0xFE, 0x00, 0x00, 0x00, 0x00, 0x00}, // char127
};

The driver code in drivers/uktty/gop/gop.c externs these symbols and directly accesses them.

/* Font metadata */
extern __u8 char_width;
extern __u8 char_height;
extern __u8 font[256][16]; /* Default font */

Generic console device interface#

A generic console device interface was proposed by PR #1464 submitted by thass0 on GitHub. This interface, exposed through a library called ukconsole, allows you to:

Register console devices, each of which uses its own underlying interfaces (serial, VGA, UEFI GOP etc).
Query registered console devices.
Write bytes to either or all registered console devices to print logs.
Read bytes from a given console device to take user input.

All of my work has been rebased onto the work done in PR #1464. The GOP driver has been modified into a console device that can now be registered to the ukconsole library.

All kernel debug messages printed using the GOP console device, with a new 8x16 font!

This means that the kernel can be configured to transparently use this GOP console device without having to change any of the existing print statements!

Refactoring#

The code was moved to drivers/uktty/gop/ from plat/common/ which was a temporary location. This was done in order to integrate with ukconsole.

In addition to this, the code underwent a substantial overhaul. It is now much cleaner!

Next Steps#

Support for all ASCII codes (like \a, \t etc) must be added.
The logs are not colored! The image above shows some weird characters being printed along with the actual logs.

These are escape codes used to color the logs themselves, which must be interpreted as such and not actually printed onto the console.
The console device must be tested against all configuration options such as CONFIG_LIBUKDEBUG_ANSI_COLOR, which dictate some logging parameters.
The code must be brought to a mergeable state by adding license information, checking the formatting etc.

Acknowledgement#

I would once again like to thank all the great Unikraft folk for their continued support! This work would not have been possible without them ❤️