Re: [Libunwind-devel] UNW_EINVAL stepping past _L_lock_686 in pthread_mutex_lock

[Jared Cantwell]

I pulled the tip of libunwind and while my test passes (libunwind
thinks it walked the whole stack), the results are incorrect.  The
second stack walked incorrectly stops at _L_lock_909 without an error,
whereas with libunwind 1.1 it stops with an error.  The second stack
should continue through to pthread_mutex_lock and all the way down to
start_thread and clone.  I've compiled gdb with additional logging in
stack walking and am in the process of comparing to the libunwind log
info.

--- not in pthread_mutex_lock ---
thread_start(void*)
start_thread
clone
---------------------------------
--- IN pthread_mutex_lock ---
sig_handler(int)
killpg
__lll_lock_wait
_L_lock_909
---------------------------------
PASS: Full stack was walked.

~Jared

On Sat, Sep 27, 2014 at 10:58 AM, Arun Sharma <address@hidden> wrote:
> On Fri, Sep 26, 2014 at 2:15 PM, Jared Cantwell
> <address@hidden> wrote:
>> I have reproduced this on ubuntu 14.04 and 13.10.  Configuration
>> information below.  I've also tested on 3.14 kernel and eglibc 2.18
>> without any luck.  Arun, if my test passes for you on 13.10 can you
>> provide information on your setup so I can compare?
>
> ubuntu 13.10
> 3.11.0-12-generic
> eglibc 2.17-93ubuntu4
> g++ 4.8.1-10ubuntu8
>
> I can't tell which version of libunwind you tested. 1.1 is likely to
> have bugs that have since been fixed.
>
>>
>> Does the fact that gdb can unwind this stack mean anything?  Like that
>> the unwind information is in libpthread in some form that libunwind
>> doesn't quite understand?
>
> This strongly suggests the unwind info is there, but your version of
> libunwind is unable to find it.
>
> There is also a possibility that gdb has a heuristic that works in the
> absence of unwind info, but libunwind's heuristic doesn't work.
>
> Steps I used to test:
>
> cd libunwind; // commit id 781d5d5
> make DESTDIR=/tmp/foo install
> g++ unwind_repro.cpp -o unwind_repro
> /tmp/foo/usr/local/lib/libunwind.a -llzma -lpthread
> ./unwind_repro // ran it 10 times
>
>  -Arun