Murilo Opsfelder Araujo [off-list ref] writes:

On Wed, Jul 25, 2018 at 05:00:21PM +1000, Michael Neuling wrote:

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 On Tue, 2018-07-24 at 16:27 -0300, Murilo Opsfelder Araujo wrote:

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This series was inspired by the need to modernize and display more
informative messages about unhandled signals.

...

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Nice.. the instruction dump would have been very handy when debugging the PCR
init issue I had a month or so back.

These things may be related :)

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What happens if we get a sudden flood of these from different processes that
overlap their output? Are we going to be able to match up the process with
instruction dump?

As to the flood of messages, ___ratelimit() makes me think that we'll
likely see some warn messages informing how many show_signal_msg()
callbacks were suppressed, instead of interleaved messages and
instruction dumps.

As to matching process with instruction dump, I believe we'd need more
information to glue them together.

What if we modify show_instructions() to accept a string prefix to be
printed along with each line?

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Should we prefix every line with the PID to avoid this?

That's possible.  An alternative would be prefixing each line with the
process name and its PID, as in the first line.  For example:

    pandafault[10758]: segfault (11) at 00000000100007d0 nip 000000001000061c lr 00007fffabc85100 code 2 in pandafault[10000000+10000]
    pandafault[10758]: Instruction dump:
    pandafault[10758]: 4bfffeec 4bfffee8 3c401002 38427f00 fbe1fff8 f821ffc1 7c3f0b78 3d22fffe
    pandafault[10758]: 392988d0 f93f0020 e93f0020 39400048 <99490000> 39200000 7d234b78 383f0040

The above can be interleaved with other messages and we'll still be able
to match process and its corresponding instruction dump.

Yeah prefixing with the comm and pid is nice.

Also the "Instruction dump:" line is a waste of space.

I prefer the x86 format, where it's prefixed with "code:", eg:

  pandafault[10758]: segfault (11) at 00000000100007d0 nip 000000001000061c lr 00007fffabc85100 code 2 in pandafault[10000000+10000]
  pandafault[10758]: code: 4bfffeec 4bfffee8 3c401002 38427f00 fbe1fff8 f821ffc1 7c3f0b78 3d22fffe
  pandafault[10758]: code: 392988d0 f93f0020 e93f0020 39400048 <99490000> 39200000 7d234b78 383f0040

cheers