How to get software recording to work?

How to get software recording to work?

[Simon Sobisch]

(gdb) record full
(gdb) continue
Continuing.
Process record does not support instruction 0xfae64 at address 
0x7ffff7df0f48.
Process record: failed to record execution log.

Program stopped.
0x00007ffff7df0f48 in _dl_runtime_resolve_xsave () from 
/lib64/ld-linux-x86-64.so.2

This is produced in an older environment with GDB 9.2; using a different 
environment with GDB 11.1:

Process record does not support instruction 0xc5 at address 0x7ffff6c79024.
Process record: failed to record execution log.

Program stopped.
0x00007ffff6c79024 in __memset_avx2_unaligned_erms () from 
/usr/lib64/libc.so.6


Can this recording be done reliably? Which places would need to be fixed 
/ adjusted to get this working?

Thanks for any pointers,
Simon

RE: How to get software recording to work?

[Metzger, Markus T]

Hello Simon,

>Thanks Markus for your answers (just in case: they weren't CC'ed to the
>mailing list, not sure if this was by intent).

It was not.  My email client sometimes removes mailing lists when I 'reply all' and I forgot to re-add it.  Thanks for pointing it out.


>> The issue is lack of AVX support in the record full instruction decoder.
>>
>>> Can this recording be done reliably? Which places would need to be fixed
>>> / adjusted to get this working?
>>
>> AFAIK record full also has issues with multi-threaded processes.  To fix the
>instruction decode issue, the best approach IMHO would be to extend the
>instruction decoder that is used for disassembly and use that for record full.
>
>Is this something Intel may have a look at?
>
>I guess Instruction/Processor specific instructions are possibly best
>implemented by the vendors, aren't them?

Intel is maintaining the binutils disassembler.  It is a bit unfortunate that record full uses a separate instruction decoder.

Given the issues with multi-threaded debuggee processes, I'm not sure how usable record full would be.  Or how much it would be used if we were to enable AVX.  I remember it adding significant recording overhead.

Regards,
Markus.
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