Oh whoa, I thought I could have an architecture neutral way to interface
with the TCG to find this out.

Yes, I do have to use the decode tree, and converting the script to output
the codes would suffice for my case. However, I do not know how to do that
at the moment. I've tried my best to understand the TCG documentation but
this appears to not be too straightforward.


On Fri, Jul 22, 2022 at 5:31 AM Alex Bennée <alex.bennee@linaro.org> wrote:

>
> Kenneth Adam Miller <kennethadammiller@gmail.com> writes:
>
> > I need to determine the set of instruction encodings that the TCG can
> support for a given platform. I am not bothered
> > whether the target runs at all, and in fact it is better if it
> > doesn't, so runtime or translate time doesn't bother me.
>
> Which architectures are you interested in? For the ones that have been
> converted to use decode tree it should be easy enough to update the
> script to emit the uncovered opcode space. However decode tree targets
> regular encoding - I think it has gained support for multiple encoding
> modes but I don't know if it can handle the irregular madness of x86.
>
> > Imagine I were adding support for more instructions for a given
> platform. I would like to check that I'm using the API
> > right. It's amazing that it's been so far and there's no way to check
> that the correct behavior occurs when a given
> > encoding is encountered regarding the TCG. A boolean result from a
> can_translate called just when the target encounters
> > the instruction would be good.
>
> Generally when the translator encounters an instruction it can't
> translate it would emit a illegal instruction exception. While you might
> be able to peek into the TCG opcode stream to see such calls to the
> relevant helpers I doubt it would be up-streamable as each front end
> will deal with illegal instructions their own way (including
> instructions that are illegal due to the current CPU operating mode).
>
> > Additionally, the ability to force the translation of arbitrary
> encodings would be good. I
> > would like to not have to engineer some binary file format.
>
> You don't need a new binary file format - just to construct an ELF with
> the stream you want. A possibly adjacent project you might want to look
> at is RISU:
>
>   https://git.linaro.org/people/peter.maydell/risu.git/about/
>
> which we've used for testing the range of the translator for a number of
> architectures.
>
> >
> > On Wed, Jul 20, 2022 at 1:37 PM Peter Maydell <peter.maydell@linaro.org>
> wrote:
> >
> >  On Wed, 20 Jul 2022 at 17:39, Kenneth Adam Miller
> >  <kennethadammiller@gmail.com> wrote:
> >  > That I know of, the TCG plugins do not allow me to feed the
> >  > QEMU instance dynamically changing opcodes. I wouldn't use
> >  > TranslatorOps if I don't have to. I want to facilitate a
> >  > use case in which the contents of the target being emulated
> >  > are changing, but it is not a self modifying target. I have
> >  > to query and interact with the TCG to find out what opcodes
> >  > are supported or not.
> >
> >  I agree that feeding opcodes into the translator isn't what
> >  TCG plugins are intended for.
> >
> >  I'm definitely not clear on what you're trying to do here,
> >  so it's hard to suggest some other approach, but linux-user
> >  code shouldn't be messing with the internals of the translator
> >  by grabbing the TranslatorOps struct. Among other things,
> >  linux-user code is runtime and TranslatorOps is for
> >  translate-time.
> >
> >  Sometimes code in linux-user needs to be a bit over-familiar
> >  with the CPU state, but we try to keep that to a minimum.
> >  Generally that involves code in target/foo/ providing some
> >  set of interface functions that code in linux-user/foo/
> >  can work with, typically passing it the CPU state struct.
> >
> >  thanks
> >  -- PMM
>
>
> --
> Alex Bennée
>