[Bug c++/20020] GDB segfault on printing objects

["keiths at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20020

Keith Seitz <keiths at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |keiths at redhat dot com

--- Comment #3 from Keith Seitz <keiths at redhat dot com> ---
(In reply to Thilo Voertler from comment #1)
> Any comment would be appreciated

Thank you for chasing this down. I have investigated this a little, and I see
this hunk from commit 492d29ea is probably the culprit:

@@ -313,18 +313,21 @@ cp_print_value_fields (struct type *type, struct type
*rea
l_type,
                }
              else if (field_is_static (&TYPE_FIELD (type, i)))
                {
-                 volatile struct gdb_exception ex;
                  struct value *v = NULL;

-                 TRY_CATCH (ex, RETURN_MASK_ERROR)
+                 TRY
                    {
                      v = value_static_field (type, i);
                    }

-                 if (ex.reason < 0)
-                   fprintf_filtered (stream,
-                                     _("<error reading variable: %s>"),
-                                     ex.message);
+                 CATCH (ex, RETURN_MASK_ERROR)
+                   {
+                     fprintf_filtered (stream,
+                                       _("<error reading variable: %s>"),
+                                       ex.message);
+                   }
+                 END_CATCH
+
                  cp_print_static_field (TYPE_FIELD_TYPE (type, i),
                                         v, stream, recurse + 1,
                                         options);

Your patch should fix that. Would you care to submit your (properly formatted)
patch (and ChangeLog) to gdb-patches@sourceware.org?

(In reply to Guillaume Morin from comment #2)
> We have started experiencing a similar crash when we switched to g++ 7.1
> with c++17 semantics.  When gdb tries to print a "static constexpr", it
> triggers a "error reading variable: Missing ELF symbol" exception and then
> crashes at the same place as the original reporter. This seems to happen
> with every release at least from gdb 7.11. I also built the git master and
> could reproduce the problem as well.

This appears consistent with this bug, thank you for reporting.

> I have a simple reproducer:
> 

Awesome! Thank you very much for this!

> Now run it with gdb:

I tried your test case (using gcc 7.0-20160916 (experimental) -- the gdb c++
compile branch) and did not reproduce the crash. I will try building something
newer. Can you give me the exact compiler version you are using? [g++ -v]

> If I compile the program above with the default c++ semantics(c++ 14), I get 
> (gdb) print *this
> $1 = {static a = <optimized out>}
> 

That appears to be another issue (which I have also investigated). I'm going to
open a new bug about this, c++/21892. Let's move the "optimized out" discussion
there.

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