Re: instrumentation, was Re: core dump analysis

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Geert,

Am 11.04.2023 um 19:19 schrieb Geert Uytterhoeven:
> Hi Michael,
>
> On Tue, Apr 11, 2023 at 6:56 AM Michael Schmitz <schmitzmic@gmail.com> wrote:
>> Am 11.04.2023 um 12:20 schrieb Finn Thain:
>>> On Sun, 9 Apr 2023, Michael Schmitz wrote:
>>>> Am 08.04.2023 um 00:06 schrieb Geert Uytterhoeven:
>>>>> On Fri, Apr 7, 2023 at 3:58 AM Michael Schmitz <wrote:
>>>>>> The easiest way to do that is to log all wait and signal syscalls, as
>>>>>> well as process exit. That might alter timing if these log messages
>>>>>> go to the serial console though. Is that what you have in mind?
>>>>>
>>>>> Store to RAM, retrieve through a new /proc file?
>>>>
>>>> Yes, that could be done, though I'd rather avoid duplicating a lot of
>>>> the generic message formatting code (printk and friends).
>>>>
>>>> I'll have a look around ...
>>>>
>>>
>>> A better solution might be be to port the existing instrumentation like
>>> ftrace, kprobes, uprobes etc. Might be a lot of work though. I wonder
>>> how portable that stuff is.

Looking at a few arch implementations, I'm utterly confused. Wouldn't 
know where to start.

>>>
>>> If you use printk, you could probably avoid most of the delays by enabling
>>> the dummy console. Then the kernel messages would be collected with dmesg,
>>> given a sufficiently large CONFIG_LOG_BUF_SHIFT. But it would be
>>> inconvenient to have no serial console available for the usual purposes.
>>
>> Can we disable the serial console after boot, by registering the dummy
>> console? Or will that just log messages to both?
>
> You can increase loglevel.

Yes, we could do that. I thought /proc has to be mounted for the 
loglevel to be changed, but I might be wrong.

OTOH, if we log wait and signal actions at level debug, and set loglevel 
to info or notice through the command line, we won't miss much of the 
usual boot messages on the serial console ...

Cheers,

	Michael


>
> Gr{oetje,eeting}s,
>
>                         Geert
>
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>