Re: [Qemu-devel] Binary translation (of code)

[Blue Swirl <blauwirbel@gmail.com>]

On Sun, May 8, 2011 at 4:05 PM, Tarmo Pikaro <tapika@yahoo.com> wrote:
>
>> In general, this is not possible. Consider for example self-modifying
>> or otherwise dynamically created code, or just code that examines
>> itself.
>
>> In some specific trivial cases it could work, and QEMU could be made
>> to abort if translation would be needed.
>
> I think self-modifying code is kinda rare case - it's made typically for
> protection againt hackers , and typically on pc side. Nintendo roms probably
> don't use this kind of
> protection.

It doesn't have to be protection, for example GCC generates
trampolines to stack when using nested functions.

> Anyway - I think even to self-modifying code could be some tricks like
> dynamically generated code.

It would be possible to save the original executable (for read
references or write references to code that change already generated
code) and invoke translator when we detect untranslated instructions.
This would amount to a full QEMU plus some kind of startup cache.

> I would be probably intrest to re-compile only modules, like .dll - but this
> would
>
> require to analyze when and how .dll being loaded. This is kinda self-modifying
> code as well ? (OS loads .DLL)

In general, a program can load anything and start executing them or
even modify previously non-executable region to become executable.