All Questions
29 questions
2
votes
0
answers
42
views
Accessing Indices Beyond Array Size in Decompiled UEFI BIOS Code
I am stuck analyzing an .efi file (extracted from a UEFI BIOS .exe package). I have commented and renamed most of the parts I am interested in, but I am having some troubles finding the last ...
- 21
0
votes
0
answers
99
views
My bootloader works on QEMU fine but no on real hardware
The bootloader is one of the hello world projects that i have found that in internet:
https://johv.dk/blog/bare-metal-assembly-tutorial.html
Before that I had tried to write some bootloader with nasm ,...
- 11
1
vote
0
answers
69
views
How to use .asm in EDK2?
I am trying to use assembly in EDK2. I build an X64 driver so I can't use inline assembly but I always get an error while trying to compile.
I am using a HeciTool.asm that only returns a 0:
section ....
- 11
1
vote
2
answers
109
views
How does the ms_abi pass between c and assembely
I am working on an OS using EFI using the ms_abi and was wondering how does it pass arguments because I am moving some systemtable info into a register but when I try to call a function using the ...
- 21
0
votes
0
answers
158
views
Why is load image returning EFI_NOT_FOUND?
I am creating a UEFI application in NASM assembly. I want to be able to give it an absolute file path to a secondary EFI file, and to use the loadImage boot service to launch that image.
The problem ...
- 426
0
votes
0
answers
63
views
why doesn't my loop work in 64 bit nasm for efi [duplicate]
I'm writing a basic bootloader for my laptop, which uses uefi, I have got booting from the usb working, printing working, exits working, everything but a simple loop.
This the the loop:
mov r10, 0x05
....
0
votes
0
answers
141
views
Is there a UEFI emulator for ubuntu
I'm trying to write a basic bootloader for my laptop, which uses UEFI. I've got the code working when I boot it from a usb, but it's just a pain to restart my computer every time I want to run my code....
0
votes
1
answer
589
views
How do I get the device path of the current running image in UEFI?
As part of a UEFI application I am writing, I would like for my application to load a second application in the same folder as this one.
However, to do this, I need to know the full file path of the ...
- 426
5
votes
1
answer
862
views
How to write 'Hello_world' EFI application in NASM?
I'm trying to write a 'Hello_world' EFI application in NASM but can't seem to be able to get it working. When I run the application (in VirtualBox), it doesn't print anything. It just hangs. Here's my ...
- 195
0
votes
1
answer
292
views
Black screen NASM UEFI
I want to boot to my NASM kernel. But it is black screen and gives error The virtual machine can not boot in VMWare.
No prints.
The codes:
kernel.asm
; generate 64-bit code
bits 64
; use relative ...
user15799783
0
votes
0
answers
48
views
Why does openVolume cause a #gd error in QEMU?
I am working on a NASM implementation of a UEFI application. One of the things I need it to do is to read files on its' file system. To do that, I am using the EFI_SIMPLE_FILE_SYSTEM protocol and the ...
- 426
0
votes
0
answers
86
views
Does the 'ret' instruction behave differently on different UEFI implementations? [duplicate]
I have a simple print string program as part of a UEFI application.
I am trying to print three strings in a row onto the screen, using the output console function OUTPUT_STRING
The part I'm struggling ...
- 426
1
vote
1
answer
651
views
Get EDID info in C (UEFI): read the ES:DI register?
I am Developing an OS, I wants to get EDID from monitor, I am found some asm code (https://wiki.osdev.org/EDID) to get edid in ES:DI registers,
mov ax, 0x4f15
mov bl, 0x01
xor cx, cx
xor ...
- 90
0
votes
0
answers
1k
views
Can I use every USB 3.0 A/A cable for Intel DCI debugging?
I successfully managed to enable DCI on my UEFI mainboard to enable debugging via a USB 3 DbC connection.
Now I need a USB 3 debug cable. I only can find one at DataPro via Google. It actually looks ...
user7145038
0
votes
0
answers
105
views
Would writing to full physical memory break the hardware?
I am playing around with UEFI and based on Specs after calling ExitBootServices i own all the memory. Are there any memory regions mapped by the CPU to some physical hardware ROMs that could be ...
user7145038
1
vote
1
answer
318
views
Cannot find OutputString Offset in UEFI Assembler Application
I want to Output a String via UEFI in a EFI Application made by Flat Assembler.
This is my Code
format pe64 dll efi
entry efimain
section '.text' code readable executable
efimain:
sub rsp, ...
user7145038
0
votes
0
answers
344
views
ARMv8 AARCH64 - Error: immediate out of range
I'm start programming assembly for ARMv8 and I'm facing an error to compare a value to create a conditional code:
First approach:
#include <AsmMacroIoLibV8.h>
var1 .8byte 0xdedededef1f1f1f1
...
- 33
5
votes
1
answer
598
views
UEFI boot services CreateEvent() returning status EFI_INVALID_PARAMETER
I'm writing a simple UEFI application in NASM assembly, and I'm trying to make an event for a free-running timer, but the call to CreateEvent always returns EFI_INVALID_PARAMETER and I'm not sure why.
...
- 561
7
votes
1
answer
1k
views
Can a UEFI machine use BIOS interrupts?
When the kernel been loaded into the memory, can it still can use BIOS interrupts?
Such as
mov AX,0E820h
int 15h
or something.
- 91
11
votes
1
answer
19k
views
How does UEFI boot mode boot flows?
The expression of this question is same as What is UEFI's boot sequence?, but it doesn't seem what I want. I'd like to know UEFI sequence in instruction perspective.
For example, in case of BIOS ...
- 725
0
votes
2
answers
1k
views
How to write a custom bootloader for mac systems?
I wrote a little bootloader in assembly and it uses BIOS interrupts and it works great on my pc. My question is, is there any possibility to make it work on Mac / Apple systems. I know that Apple ...
0
votes
1
answer
720
views
Having trouble calling ExitBootServices from a bare-bones PE+ uefi application made with nasm
I have made a PE+ UEFI application in nasm and have been able to use EFI_BOOT_SERVICES to print text, to load the GOP, and when I call GetMemoryMap the return value is EFI_SUCCESS (0) and I can return ...
2
votes
1
answer
7k
views
Assembly - How to set graphics mode in UEFI (No VGA, No BIOS, Nothing deprecated)
Tools I'm using: nasm, qemu-system-x86_64.
Operating System I'm on: Windows 10.
So I checked out the "Real Mode OS Warning" at https://wiki.osdev.org/Real_Mode_OS_Warning
What the article seems to ...
1
vote
0
answers
92
views
Send bytes to SPI controller using Assembly
I am studying UEFI Firmware development. For debuging purpose, I need to send some read / write commands to SPI controller.
Is there any way to communicate with SPI controller using assembly language?...
- 141
1
vote
0
answers
216
views
EFI? Byte Code (micro)optimizations
Are there any good practices for optimizing and micro-optimizing EFI Byte code (or bytecode in general) for speed given that instructions are executed in strict order? Like maybe one instruction is ...
- 9,272
3
votes
1
answer
2k
views
Broken CPUID brand string?
I am printing some information about CPU in my OS using CPUID instruction.
Reading and printing vendor string(GenuineIntel) works well, but reading brand string gives me little strange string.
ok ...
- 261
26
votes
5
answers
18k
views
How does UEFI work?
I was studying about bootloaders when exactly came upon the term UEFI. I can understand some things about UEFI. But still, In what mode(Real,Protected,Long) does a system with UEFI start? If normal ...
- 359
4
votes
2
answers
2k
views
How can a Bootloader written in x86 Assembly be written to a USB Flash drive and support both BIOS and UEFI?
Recently I have written a bootloader in x86 Assembly. The bootloader does not do anything special right now, but I am planning to load my own kernel with this bootloader. I am able to write the ...
- 23k
21
votes
3
answers
14k
views
Writing an OS with UEFI [closed]
I haven't been coding much lately, but I've decided I want to start working on OS development again. Recently I heard about a system better than BIOS. I want to develop an OS for a platform that uses ...
- 2,353