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Index > Linux > Framebuffer, putpixel, segfault

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lavrin



Joined: 22 Dec 2009
Posts: 2
lavrin
Hello, everyone!

I've got a question to ask about a framebuffer program I'm trying to put together for a low-level programming course at my university.

To the point. Target architecture is x86-64. I've managed to map the framebuffer device file /dev/fb0 to memory. However, when I try put a pixel on screen, the program segfaults. I haven't got even a vague idea what may be the cause.

I would be grateful for any hints. My situation is pretty hard, as I don't know anyone skilled in this field. The source is accessible here [1].

Regards,
Radosław Szymczyszyn

--
[1]: http://ernie.icslab.agh.edu.pl/~lavrin/fb.asm
Post 22 Dec 2009, 00:40
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17628
Location: In your JS exploiting you and your system
revolution
I think your problem is here:
Code:
    mov   dword [fb + rbp], 0xeeeeee00
...
        fb        rq  1    
'fb' is allocated as only one qword but you are writing to it with offsets in rbp.

Perhaps you can try something like this:
Code:
    mov   rax,[fb]
    mov   dword [rax + rbp], 0xeeeeee00    
Post 22 Dec 2009, 00:51
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lavrin



Joined: 22 Dec 2009
Posts: 2
lavrin
You're perfectly right. Thanks!
Post 22 Dec 2009, 00:56
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