Re: [PATCH] libdwfl: Do not dlopen libdebuginfod if DEBUGINFOD_URLS is unset or empty

[Mark Wielaard <mark@klomp.org>]

Hi Vitaly,

On Thu, 2020-11-05 at 17:44 +0300, Vitaly Chikunov wrote:
> Avoid calling expensive dlopen at the cost of an extra getenv check when
> we already know it would not be needed.
> 
> This mirrors the getenv check from debuginfod_query_server.

I am sympathetic to this. It would have been a nicer way to fix the
valgrind issue I recently had with dlopen having unsuppressible errors
on some older glibc versions. But it also makes it so that an
application can never use the debuginfod support afterwards. The
current debuginfod_query_server check is late enough that an
application could set DEBUGINFOD_URLS just before a Dwarf lookup.

What do you think? Is that a valid use case?

Should we maybe introduce setting debuginfod_urls on Dwfls so that an
application can explicitly indicate they want to use debuginfod lookups
and then dlopen libdebuginfod late? The problem with doing the dlopen
late is that we also need libcurl and initializing libcurl (as done by
libdebuginfod) is not thread-safe.

Cheers,

Mark