Re: more backtraces

On 2019-12-04 20:59, Andres Freund wrote:
> On 2019-12-04 20:45:25 +0100, Peter Eisentraut wrote:
>> In the previous discussions on backtrace support, some people asked for
>> backtraces in more situations.  Here is a patch that prints backtraces on
>> SIGABRT, SIGBUS, and SIGSEGV signals.  SIGABRT includes assertions and
>> elog(PANIC).
> 
> Hm. Can we really do that somewhat reliably like this?

I've seen reputable programs that do all kinds of things in SIGSEGV 
handlers, including running user-defined programs, without taking any 
special precautions.  So it seems possible in general.

> I'd suspect that
> there'll be some oddities e.g. for stack overflows if done this way. To
> my knowledge it's not a good idea to intercept SIGBUS/SIGSEGV without
> using a separate signal stack (cf. sigaltstack) - but using a separate
> stack could also make it harder to determine a correct backtrace?

Didn't know about that, but seems useful.  I'll look into it.

> It'd be bad if the addition of backtraces for SEGV/BUS suddenly made it
> harder to attach a debugger and getting useful results. Even
> disregarding the previous concerns, we'll get less useful debugger
> interactions due to this, e.g. for things like null pointer derefs,
> right?

The backtrace and level of detail jumping around between frames I get in 
lldb looks the same as without this.  But it might depend.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services