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flat assembler > Main > EFI programming

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Fulgurance



Joined: 27 Nov 2017
Posts: 49
Hello, i have just little question, is it possible to program EFI boot without PE format ?
Post 03 Jan 2018, 16:57
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zhak



Joined: 12 Apr 2005
Posts: 489
Location: Belarus
What is EFI boot in your understanding?
Post 09 Jan 2018, 16:08
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Fulgurance



Joined: 27 Nov 2017
Posts: 49
I'm not sure i really understand. I think the efi replaces the bios, and it's a firmware developed in C.I guess we do not need a traditional MBR. I think that need GPT disk format, but i would like to know if it's possible to make another custom method

However, I have the impression that the EFI only recognizes the PE format.

I want you to explain me
Post 09 Jan 2018, 16:20
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zhak



Joined: 12 Apr 2005
Posts: 489
Location: Belarus
In a couple of words, UEFI firmware replaces BIOS but provides BIOS emulation for compatibility purposes. It understands PE32+ file format for executable images and FAT file systems. You can add support for other file formats and file systems with the help drivers (which should be in PE file format). Boot flow will be as follows: firmware boots your custom boot loader from a bootable device. The boot loader loads additional drivers (for example, to provide ext file systems support) and continues with boot process (loads kernel from ext fs).
Post 12 Jan 2018, 14:35
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Fulgurance



Joined: 27 Nov 2017
Posts: 49
Okay, quite simply, impossible with full custom executable. I must use PE format.

Without memory restricted use, is it possible to do same thing in EFI with BIOS programming ?
Is it possible to start in BIOS with good screen resolution ?
Post 12 Jan 2018, 16:24
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DimonSoft



Joined: 03 Mar 2010
Posts: 451
Location: Belarus
Fulgurance wrote:
Is it possible to start in BIOS with good screen resolution ?

Not sure if I understand your question, but you don’t have control over what video mode BIOS sets up before your bootloader is started, the same applies to BIOS emulation in UEFI (since it’s emulation, remember?).

So, if you choose to write a BIOS bootloader, you have a text-mode (03h, AFAIR). After that you can either deal with good old modes, you can try VESA modes (if supported by emulaion layer) or you can load your OS, which in turn loads video drivers and then uses any resolution your video adapter supports.
Post 13 Jan 2018, 10:21
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