Dear Wolfgang Denk,
On 02/04/2013 09:26 PM, Wolfgang Denk wrote:
Dear Nikita Kiryanov,
In message 1359977979-28585-2-git-send-email-nikita@compulab.co.il you wrote:
Currently code that displays BMP files does two things:
- assume that any address is a valid load address for a BMP
- access in-memory BMP header fields directly
Since some BMP header fields are 32 bit wide, this has a potential for causing data aborts when these fields are placed in unaligned addresses.
Create an API for safely accessing BMP header data, and compile it with $(PLATFORM_NO_UNALIGNED) to give it the ability to emulate unaligned memory accesses.
Frankly, I think this is overkill. U-Boot is a bootloader, and it is supposed to be lean and eficient. We don't have all levels of safety systems and protective devices as in, for example, an aircraft. You are supposed to know what you are doing, and if you ignore the rules, you will quickly see the results yourself.
[...]
You talk about BMP header - but we also have alignment requirements for image headers, well, even for a plain "md" or "mw" command. And none of these provide any protection against accidsential (or intentional) access to unaligned addresses.
That's true, but when md traps you simply restart the board and everything's fine. If displaying a splash screen traps- you're stuck. I'm not saying we should start implementing protection against every possible mistake, but when the repercussions are this serious I feel that protection is in order.
There's a difference between a bicycle with no training wheels and one that falls apart when you turn it the wrong way.
My recommendation is: just don;t do it, then.
Best regards,
Wolfgang Denk