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NVIDIA Hack for Haiku and
Widescreen LCDs

Introduction

The problem is that your video card does not have a VESA resolution that matches your LCD's native resolution. For example, your highest VESA mode is 1280x1024, and your LCD has 1920x1080. The result is that the whole Haiku interface will be stretched and scaled to fill the screen. This is very undesirable because everything will be blurry and distorted. The solution is to disable this default up-sampling.

Requirements

1. Any recent nVidia card (7300GT, 8400GS, and 9800GT)

2. Any digital LCD connected via DVI (SyncMaster XL2270)

Method

The on-chip scaler can be disabled with a mere 12 bytes of machine code. This code must be executed in real mode, therefore it must be called early on in the boot process. A good place for it is the MBR (stage0) or the PBR (stage1). It may also be placed in your video card's BIOS or even your PC's BIOS, if you are feeling adventurous and want a permanent solution.

For simplicity, let's inject the disabler code into Haiku's PBR. This is the first sector of the partition (/dev/disk0s4 in this example) where Haiku is installed and it just happens to be full to the brim, as shown below.

Hexdump of the original PBR

Modifying/Hacking the PBR

We need to find a codecave that is 16 bytes long: 12 bytes for the disabler code, 2 for an enclosing pusha/popa sequence, and 2 more for a jmp opcode. We have no choice but to overwrite some unused text messages, which are located between offsets 0x199 and 0x1E3. This works out just fine because those error messages are only seen if there's a problem. And if there is a problem booting, you will see gibberish instead of the actual error message.

Step 1: Inject the 16-byte code at offset 0x1A0 with the following two commands.
XSTR='\x60\xb8\x14\x4f\xb3\x02\xb7\x01\xb9\x01\x00\xcd\x10\x61\xeb\x9a'
printf $XSTR | sudo dd of=/dev/disk0s4 bs=1 seek=416

We also need to redirect the flow of execution so that this code is called. The way to do this without destroying any critical code is to find a jump instruction and modify it to point to the offset of our code. At offset 0x194 you will find such a jump (EB B4) that returns back to 0x14A, which is found by (0xB4-0x100)+0x2+0x194. Calculate the 2nd byte for the new forward jump as follows: 0x1A0-0x194-0x2=0x0A.

Step 2: Change the B4 to 0A with this command:
printf '\x0A' | sudo dd of=/dev/disk0s4 bs=1 seek=405

Note that the end of the code in step 1 already has a jump opcode (EB 9A) that returns execution back to offset 0x14A. The 9A is the back jump's 2nd byte and is calculated as follows: 0x14A-(1A0+0xE)-0x2+0x100, where 0xE is the size of the disabler code (12 bytes) plus the enclosing pusha/popa opcodes (2 bytes), so 12+2=14 or 0xE.

When these 17 bytes are changed, the code is executed without interfering with Haiku's boot process. Here's a screenshot of what your PBR should look like after the changes. And if you are not comfortable with the command line, you can also edit your PBR with any hex editor and type in the 17 bytes manually.

Hexdump of the Modified PBR

The 17 changed bytes are highlighted in yellow.

Other Boot Sectors

If you use GRUB as your main bootloader, you are in luck because at offset 0x0 there is a jump (EB 63) followed by one nop (90) and enough nulls for the code plus much more. The jump goes to offset 0x65 (0x63+0x2+0x0). You won't need the enclosing pusha/popa, but you will need to add a trailing jump. Calculate the new forward jump's 2nd byte as follows: 0x65-0xC-0x2 = 0x57. Now inject the code (using the 5th partition as an example) at offset 0x0 with these commands:
XSTR='\xb8\x14\x4f\xb3\x02\xb7\x01\xb9\x01\x00\xcd\x10\xeb\x57'
printf $XSTR | sudo dd of=/dev/disk0s5

And if you use Windows as your main bootloader, you can still inject the code in your NTFS partition, using the a similar method.

Conclusion

Now when you reboot, you'll notice that the BIOS will go through it's various stages, and the text will be large and stretched -- just as it always was. But when the new PBR code is loaded and executed, the Haiku loader icons will not be stretched and they will be small and tack sharp. Once Haiku is loaded it may look like a small window in the center of the display, but it's not. What you are seeing is a one to one pixel ratio.

If you have a recent nVidia video card AND a digital LCD monitor connected via DVI, you can modify your boot sector and enjoy a much improved Haiku experience.

This page was last revised on July 14, 2011
Copyright © 2011 Anthony D'Agostino
All rights reserved.