RE: [PATCH] Adding ability to change disassembler syntax in TCG plugins

[Mikhail Tyutin <m.tyutin@yadro.com>]

> On 2/15/23 18:17, Mikhail Tyutin wrote:
> > ping
> >
> > patchew link:
> > https://patchew.org/QEMU/7d17f0cbb5ed4c90bbadd3992429006f@yadro.com/
> >
> > 10.02.2023 18:24, Mikhail Tyutin wrote:
> >> This patch adds new function qemu_plugin_insn_disas_with_syntax() that allows TCG
> >> plugins to get disassembler string with non-default syntax if it wants to.
> >>
> >> Signed-off-by: Mikhail Tyutin <m.tyutin@yadro.com>
> 
> Why?
> 
> It's certainly not very generic, exposing a disassembly quirk for exactly one guest
> architecture.  I mean, you could just as easily link your plugin directly to libcapstone
> via qemu_plugin_insn_data().
> 
> 
> r~
 
I agree it can be done outside of Qemu using another disassembler library. However,
there are few reasons to do it in Qemu from architecture standpoint:

1. To have a single place of instruction decoding logic. TCG has to decode guest instructions
anyway. If plugins add another decoder, it causes double work and prone to errors (however
current implementation does double decode work anyway). For example, TCG might support
new instruction which is not available in external decoder yet.

2. Under the hood Qemu uses different implementations of decoder (in addition to capstone)
which is not exposed in public interface. If there is a need to configure its output, proposed
API allows that as well.

3. If multiple plugins want to use another disassembler syntax, they have to share
implementation as utility function.