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

[Lluís]

Tarmo Pikaro writes:
>> It would be much easier to ship an executable containing both the guest
>> application and qemu, so that executing it starts qemu with a
>> pre-defined configuration and runs the guest binary.
>
> - Binary recompilation would allow faster execution than emulated code

QEMU does precisely that, using a JIT. You wouldn't obtain much more
performance by generating a pre-translated binary instead of using
QEMU's JIT. And that's without taking into account the difficulties
associated with the static binary analysis that would be required (as
others have already pointed to you to in previous mails).


> - qemu constantly changes (based on amount of patches provided in this
> mail list) - in order to keep image+qemu working - simplest way is to convert 
> into
> executable. Btw - qemu could be used as a bootstrap to image as well.
> :-)

Maybe you didn't understand what I was saying. Think of it as a
self-extracting executable that contains both a specific qemu binary, as
well as the guest binary you want to execute. When you execute that
bundle, it transparently extracts both components (qemu + the guest
application) and starts qemu to execute that application.

Still, this is a poor approach from the software maintenance point of
view, and falls into the kind of strategies that windows application
developers use (bundle private copies of each library the application is
going to use).


> - And finally modular "emulation" - it would be possible to recompile 
> individual
> .dll to another os.

I suppose you meant another architecture, as recompiling to another OS
makes no sense on the general case (can have a completely different set
of syscalls).

Still, I don't see the point of translating a single library instead of
the whole application (specially when you have access to a library
compiled for you target architecture, or even better access to the
source code to compile that library to whatever target you desire).


> Side effects would be:
>
> - More difficult to debug - since mapping to original binary image should be 
> somehow
> maintained - if register dump helps anyhow the developer.

As others have told you, qemu already has an interface to allow gdb to
debug the guest application.


Lluis

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