Re: [RFC PATCH v3 11/11] tests: add plugin asserting correctness of discon event's to_pc

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 12/5/24 05:10, Julian Ganz wrote:
> Hi Pierrick,
> 
> December 5, 2024 at 12:33 AM, "Pierrick Bouvier" wrote:
>> On 12/2/24 11:41, Julian Ganz wrote:
>>
>>>   +/*
>>>   + * Copyright (C) 2024, Julian Ganz <neither@nut.email>
>>>   + *
>>>   + * License: GNU GPL, version 2 or later.
>>>   + * See the COPYING file in the top-level directory.
>>>   + */
>>>
>> Would be nice to include a description of the plugin here.
> 
> Agreed. I'll include one next time.
> 
>> When booting an arm64 vm, I get this message:
>> Trap target PC mismatch
>> Expected: 23faf3a80
>> Encountered: 23faf3a84
>>
>>   From what I understand, it means that the next_pc we have is incorrect.
> 
> Yes, this is indeed incorrect, and also a perfect example why this test
> plugin exists. There are likely other errors lurking in target specific
> code. Did you happen to also log interrupts? Do you remember what image
> you used?

I used exactly this:

./build/qemu-system-aarch64 -plugin 
./build/tests/tcg/plugins/libdiscons.so -smp 4 -M virt -d plugin -m 8G 
-device virtio-blk-pci,drive=root -drive 
if=none,id=root,file=./debianaarch64.img -M virt -cpu max,pauth=off 
-drive if=pflash,readonly=on,file=/usr/share/AAVMF/AAVMF_CODE.fd -drive 
if=pflash,file=./AAVMF_VARS.fd

The arm64 image is a vanilla debian stable I installed.
AAVMF* files come from qemu-efi-aarch64 debian package.

> 
> Btw: this also illustrates another issue I have with from_pc: we can
> test the behavior for to_pc, but doing this meaningfully for from_pc
> via a plugin is next to impossible because the instruction it points to
> is not observable via an exec callback. At least not in the general
> case, even not if we only consider a single type of event.
>

We can store the next_expected pc for each instruction (from 
current_instruction + insn_length), and we should be able to compare 
that with the expected from_pc.
This is mostly what contrib/plugins/cflow.c does.

With that, we can test from_pc.

> Regards,
> Julian Ganz