[Bug fortran/17989] New: gdb hangs on some Fortran stack frames

["tom.k.cook at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=17989

            Bug ID: 17989
           Summary: gdb hangs on some Fortran stack frames
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: fortran
          Assignee: unassigned at sourceware dot org
          Reporter: tom.k.cook at gmail dot com

Overview:  GDB hangs when trying to display some Fortran stack frames.

Platform: Linux 3.13.0 x86_64 SMP (Ubuntu Trusty)

Steps to reproduce:  Unknown.  Sorry!  I'll give as much information as I can.

The software being debugged is mixed Fortran/C++.  The main method is in
Fortran but the executable is linked using G++.  The compiler is GCC 4.8 (for
both Fortran and C++) but I have confirmed the bug when compiling with GCC 4.9.
 I have a fairly recent GCC HEAD (early January) build around and could try
that if it might be useful.

GDB hangs when attempting to display certain stack frames (eg. when a
breakpoint is hit, or when 'finish' is used to move up a frame, or when 'bt' is
used).  'info line' and 'list' still work in these situations.

The problem always happens with Fortran stack frames, including when there are
no C++ frames on the stack.

The Fortran code is compiled with '-g -cpp -ffixed-line-length-none
-ffree-line-length-none -fcoarray=single -fno-underscoring -fPIC'.

The executable is linked with '-g', objects and libraries.

When gdb hangs, it is consuming 100% CPU (ie one CPU core).

The hang can be interrupted with Ctrl-C and the debugging session continued
normally (so long as you don't want to display the call stack etc).

I have checked that both GDB 7.7 (Ubuntu Trusty) and a fresh build from git
latest today, using GCC-5.0 latest-as-of-early-January, display this problem.

I have tried to reproduce the bug on a very simple Fortran/C++ project but have
not been able to.

Any suggestions on how to fix this, or on steps I might take to reliably
reproduce it, will be gratefully received.  I have a build of gdb
latest-of-today and could debug gdb itself if this will be useful. 
Unfortunately the Fortran/C++ code being debugged when the problem occurs is
commercial and can't be shared.

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