Re: [PATCH v2 2/2] docs/devel: tvg-plugins: add execlog plugin description

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

Alexandre IOOSS <erdnaxe@crans.org> writes:

> [[PGP Signed Part:Undecided]]
> On 6/22/21 10:48 AM, Alex Bennée wrote:
>> Alexandre Iooss<erdnaxe@crans.org>  writes:
>>> [...]
>>> +
>>> +The execlog tool traces executed instructions with memory access. It can be used
>>> +for debugging and security analysis purposes.
>> We should probably mention that this will generate a lot of output.
>> Running the admittedly memory heavy softmmu memory test:
>>    ./aarch64-softmmu/qemu-system-aarch64 -D test.out -d plugin \
>>      -plugin contrib/plugins/libexeclog.so  \
>>      -cpu max -serial mon:stdio -M virt \
>>      -display none -semihosting-config chardev=serial0 \
>>      -kernel ./tests/tcg/aarch64-softmmu/memory
>> generates a 8.6Gb text file. I suspect once this is merged you might
>> want to look at options to target the instrumentation at areas of
>> specific interest or abbreviate information.
>
> Yes! In my downstream version I am triggering the beginning and the
> end of trace acquisition by matching two virtual addresses of GPIO
> device access. This works in my case because I'm also using the same
> GPIO for triggering an oscilloscope, but maybe we would like to
> upstream something more generic.
>
> I'm still thinking about this (maybe for a later patch) but I believe
> it would be nice to have the following:
>  - If no argument is given to the plugin, log everything.
>  - Allow the user to specify either a memory address, an instruction
>    virtual address or an opcode that would start the acquisition.
>  - Same to stop the acquisition.

Sounds reasonable to me.

> This would look like this to start/stop acquisition using GPIO PA8 on
> STM32VLDISCOVERY:
>
>   ./arm-softmmu/qemu-system-arm -M stm32vldiscovery \
>     -kernel ./firmware.elf -d plugin \
>     -plugin libexeclog.so,arg=mem:1073809424,arg=mem:1073809424

I quite like the formats you can use for -dfilter, for example:

  0x1000+0x100,0x2100-0x100,0x3000..0x3100

it might even be worth exposing qemu_set_dfilter_ranges as a helper
function to plugins to avoid copy and paste.

So what would your above command trigger? A write to 1073809424 would
start the trace and the next write to the same address would stop it?

> I would like to hear other users opinion on this, because I fear I
> might implement something too specific.
>
> Thanks,
> -- Alexandre
>
> [[End of PGP Signed Part]]


-- 
Alex Bennée