Re: New capabilities for plugins

["Alex Bennée" <alex.bennee@linaro.org>]

Florian Hofhammer <florian.hofhammer@epfl.ch> writes:

> Hi Alex, hi Pierrick,
>
> I'm taking the freedom to reply to both of you at the same time, I
> hope you don't mind :)
>
> On 04/08/2025 18:05, Alex Bennée wrote:
>>> I was wondering whether the QEMU community would be open to extending
>>> the plugin API so that a plugin can fully emulate a syscall without
>>> the original syscall being executed by QEMU.
>>
<snip>
>> Another option would be to have a set_pc function that would restart
>> the execution at new PC. Then the vcpu_syscall_cb callback could set
>> the PC to post the syscall with whatever state it wants to set up.
>
> Such a set_pc functionality is already covered with the register write
> API, as long as I have a handle to the PC register, right? Please do
> correct me if I'm misunderstanding something here!

Ahh we should make that clear. It requires special handling as the PC
isn't automatically updated every instruction. For analysis this isn't a
problem as the TB itself knows the vaddr of each instruction so can save
it if it wants.

Currently if you write to the PC it won't change flow - and it will
likely be reset as we exit the syscall.

c.f. https://gitlab.com/qemu-project/qemu/-/issues/2208

>
> Thanks for your input,
> Florian

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro