Changing VESA resolution in Long/Pmode

[tantrikwizard]

I'm just waiting for, say, around next Tuesday for a new thread entitled "Stupid bios modifies segment registers"

[gravaera]

^^^

Nah. It'll come a little later than that. Right now I'm a bit hassled with Uni exams.

[iammisc]

Honestly just use an emulator or vm86 mode, it's much simpler.

[Craze Frog]

If you emulate it, it won't really be able to change the video mode, right?

[Brendan]

Hi,

If you emulate it, it won't really be able to change the video mode, right?

You'd emulate the CPU while using the real video device...


Cheers,

Brendan

[tharkun]

By simply padding it with some NULL bytes here and there you can not turn it into working 32-bit code.

http://forum.osdev.org/viewtopic.php?t=10321

AFAIK, if you pad it, and the add the 0x66 prefix, it should work.
Please correct me if I'm wrong.

[mnovotny]

You're wrong. The instructions aren't 32 bit in size while in 32 bit mode, nor they are 16 bit while in 16 bit mode.
Basic instructions usually have only one byte opcode and several other bytes of additional data. The size of instructions isn't fixed!

xor eax, eax
mov eax, 0

These two instructions do exactly the same, yet the first instruction is shorter.

[Craze Frog]

xor eax, eax
mov eax, 0

These two instructions do exactly the same, yet the first instruction is shorter.

No, they don't do the same thing. xor modifies eflags.

[mnovotny]

Bah, detail...

[Cognition]

Instruction sizes aside, segmentation will actually work properly in the compatibility sub mode of long mode. Fully translating or recompiling instructions shouldn't be necessary really as you can run in 16-bit protected mode with segmentation. Flat model segmentation only applies to code actually executing in 64-bit mode. It shouldn't be too hard emulate real mode segmentation via the GDT and setting up something resembling a virtual monitor to catch a few choice instructions and deal with the final IRET.

[Combuster]

Having segmentation or not, it won't work. Real mode segmentation != protected/compatibility mode segmentation.

[Cognition]

Edit: Scrap the idea, overall it's more trouble then it's worth really.