[Bug gdb/19530] New: Sometimes 'step' and 'next' don't stop but behave just like 'continue'

["azuhoo at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=19530

            Bug ID: 19530
           Summary: Sometimes 'step' and 'next' don't stop but behave just
                    like 'continue'
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: azuhoo at gmail dot com
  Target Milestone: ---

So far I don't have a recipe to reproduce this with a small test application or
any publicly available application but I can reproduce it easily, although it
never occurs on the same line in my test scenario which consists of setting a
breakpoint, running the application until the breakpoint and then stepping.

The problem occurs with gdb built myself from git as of yesterday
(8424cc978c8c76aca7945d50408762de65646095) and from tag gdb-7.9.0-release, when
debugging a 32bit application in a 64bit Kubuntu 15.10 x86_64 system (libc
2.21-0ubuntu4, kernel 4.2.0-25).

If I try to reproduce it with gdb built from tag gdb-7.8.2-release or
gdb-7.7.1-release I get (infrun.c line number is slightly different with
7.7.1):

infrun.c:1986: internal-error: resume: Assertion `pc_in_thread_step_range (pc,
tp)' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.

One bug report about that assertion mentions that the debugged application is
heavily multi-threaded. The application I'm debugging has 113 threads.

I don't recall facing this problem in Ubuntu 14.04 64bit with its gdb
(7.7.1-0ubuntu5~14.04.2) and I've used that to debug the same application a
lot, so it is certainly possible the problem is not in gdb but in some
kernel/libc feature that it uses.

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