Re: Plugin Memory Callback Debugging

[Alex Bennée]

Aaron Lindsay <aaron@os.amperecomputing.com> writes:

> Sorry, left off the very end of my timeline:
>
> On Nov 18 16:58, Aaron Lindsay wrote:
>> I have, so far, discovered the following timeline:
>> 1. My plugin receives a instruction execution callback for a load
>>    instruction. At this time, cpu->plugin_mem_cbs points to the same
>>    memory which will later be freed
>> 2. During the handling of this callback, my plugin calls
>qemu_plugin_reset()

The final plugin reset should only execute in the safe async context
(i.e. no other vCPUs running code). That flushes all current generated
code.

>> 3. Ostensibly something goes wrong here with the cleanup of
>>    cpu->plugin_mem_cbs???

This may be missed by the reset path (hence your patch) but it should be
being reset every instruction we instrument.

>> 4. Step 2 triggers the TBs to be flushed, which frees the memory pointed
>>    to by cpu->plugin_mem_cbs 
>
> 5. A store exclusive instruction is translated and then executed, which
>    requires the use of a helper. When executed, this helper checks
>    cpu->plugin_mem_cbs, which is non-null, so it attempts to dereference
>    and use it, resulting in the assertion.

It should be being reset for each instruction I think.

>
> -Aaron


-- 
Alex Bennée