[Bug web/98875] DWARF5 as default causes perf probe to hang

[mark at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98875

Mark Wielaard <mark at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |mark at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-02-19
          Component|debug                       |web

--- Comment #4 from Mark Wielaard <mark at gcc dot gnu.org> ---
(In reply to Paul Clarke from comment #3)
> The IBM Advance Toolchain supports SLES 15, where the latest version of
> libdw is 0.168. We'll work around the issue by reverting the commit for the
> version of GCC included with the Advance Toolchain.

Yes, that is probably reasonable when targetting a distro that is so old that
it doesn't have any tooling to support DWARF5.

Still you might want to request that the perf tool be fixed to simply skip the
DWARF5 data instead of going into an infinite loop. That bug could trigger for
any DWARF that old perf/libdw doesn't know about and it really should just skip
it. The fix for that really is just a oneliner.

> I didn't see any update to the GCC documentation regarding the disruptive
> nature of the change causing the problem other than "[DWARF] Version 5
> requires GDB 8.0 or higher".
> 
> Should there be something about libdw as well?  Anything else?

You are right. I'll submit an update for the GCC 11 Release Notes to document
things.