Re: [Qemu-devel] Funny Bash Script ...

[Herbert Poetzl]

On Sun, Feb 13, 2005 at 11:57:37AM +0400, Brad Campbell wrote:
> Herbert Poetzl wrote:
> >Hi Folks!
> >
> >there is a funny bash script available at
> >
> >  http://vserver.13thfloor.at/Stuff/QEMU/rev_01.sh
> >
> >using this on object files (like the kqemu-mod-i386.o)
> >produces interesting output, which will compile nicely
> >with gcc to something very similar of the original ..
> 
> Anyone can disassemble a binary and re-compile it. 

sure, that's why this script is there ... ;)

> Understanding exactly how it works is another story entirely. 

agreed, but understanding binary code is harder ;)

> I believe you would be in violation of the license if you 
> distributed the de-compiled source, so what do you gain by 
> doing this?

well, I'm pretty sure that most of the current qemu
hackers are able to _understand_ readable assembler
code, so it might not be that complicated ...

> In addition, we are talking kernel code here. 

yes, I'm aware of that, but let me assure you, this
kernel code is much simpler than most of the userspace
part qemu folks are working with/on ...

> The sort of stuff where random compiler optimisations can cause 
> catastrophic failures. 

of course, and some hackers have been eaten by a grue!

> Can you guarantee by doing this you are generating exactly the 
> same code as you started with? 

nobody wants to do that, otherwise you could take the
object file and be done, nevertheless, comparing the
disassembled code of two object files usually sheds
some light on the differences (i.e. with diff)

> I would certainly be loathe to trust the compiled binary.

but an unknown, proprietary object file nobody takes
liability for you trust ... i.c. 

best,
Herbert

> Brad
> -- 
> "Human beings, who are almost unique in having the ability
> to learn from the experience of others, are also remarkable
> for their apparent disinclination to do so." -- Douglas Adams
> 
> 
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