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Re: "Cannot find new threads" on Fedora 9, but not on CentOS 5 (?)

From: Andrew Lofthouse <loftyhauser at gmail dot com>
To: gdb at sourceware dot org
Date: Tue, 28 Oct 2008 21:15:01 -0400
Subject: Re: "Cannot find new threads" on Fedora 9, but not on CentOS 5 (?)
References: <49065BBD.3050800@gmail.com> <8ac60eac0810271741h135f077bj2c3fcd7391e89ed7@mail.gmail.com> <4906615E.50606@gmail.com> <8ac60eac0810271836saf8c28pb1392b77c7926be0@mail.gmail.com>
Reply-to: ajloft at umich dot edu

Sorry for the delay; I don't have access to my personal e-mail account at work...

Paul Pluzhnikov wrote:

- What does 'ldd /path/to/app' say?
- What does 'nm /path/to/libpthread.so.0 | grep _version' say (where
  /path/to/libpthread.so.0 is the one which ldd prints)?

Hmm, ldd does not list libpthread.so.0:

[andrew@fedora-vm ufs]$ ldd /usr/local/bin/ufs2oogl2D
        linux-gate.so.1 =>  (0x0012e000)
        libufs2D-0.9.so.2 => /usr/local/lib/libufs2D-0.9.so.2 (0x0012f000)
        libgts-0.7.so.5 => /usr/local/lib/libgts-0.7.so.5 (0x001d8000)
        libgmodule-2.0.so.0 => /lib/libgmodule-2.0.so.0 (0x00228000)
        libdl.so.2 => /lib/libdl.so.2 (0x0022c000)
        libglib-2.0.so.0 => /lib/libglib-2.0.so.0 (0x00231000)
        libm.so.6 => /lib/libm.so.6 (0x00312000)
        libc.so.6 => /lib/libc.so.6 (0x0033b000)
        libselinux.so.1 => /lib/libselinux.so.1 (0x004a4000)
        /lib/ld-linux.so.2 (0x00110000)

But, gdb still seems to use libpthread when debugging the application (see below).

This is most likely result of "pilot error" (stripping
libpthread.so.0, or incomplete installation of glibc), and has
nothing to do with actual version of GDB.
Except that libpthread.so.0 is not stripped (on any of the installations).
How do you know that?

Now I'm confused. It looks like the non-debug library is not stripped, but the debug library is stripped (?):

[andrew@fedora-vm ufs]$ file /lib/libpthread-2.8.so /lib/libpthread-2.8.so: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), for GNU/Linux 2.6.9, not stripped

[andrew@fedora-vm ufs]$ file /usr/lib/debug/lib/libpthread-2.8.so.debug /usr/lib/debug/lib/libpthread-2.8.so.debug: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), for GNU/Linux 2.6.9, stripped

Now, looking in gdb, it looks like gdb is using /lib/libpthread.so.0, but can't find its symbols:

[andrew@fedora-vm ufs]$ gdb /usr/local/bin/ufs2oogl2D GNU gdb Fedora (6.8-1.fc9) Copyright (C) 2008 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "i386-redhat-linux-gnu"... (gdb) run -T "rho" < UAM10_002_UFS-005000.sim > test.plt Starting program: /usr/local/bin/ufs2oogl2D -T "rho" < UAM10_002_UFS-005000.sim > test.plt

Detaching after fork from child process 8745.
[Thread debugging using libthread_db enabled]
Error while reading shared library symbols:
Cannot find new threads: generic error
Cannot find new threads: generic error
(gdb) info share
From        To          Syms Read   Shared Object Library
0x00110810  0x0012724f  Yes         /lib/ld-linux.so.2
0x0013ef00  0x001ca5d8  Yes         /usr/local/lib/libufs2D-0.9.so.2
0x001dfb80  0x00221638  Yes         /usr/local/lib/libgts-0.7.so.5
0x00228c50  0x00229cc8  Yes         /lib/libgmodule-2.0.so.0
0x0022ca60  0x0022da68  Yes         /lib/libdl.so.2
0x002401f0  0x002bf4d8  Yes         /lib/libglib-2.0.so.0
0x00315420  0x0032fe48  Yes         /lib/libm.so.6
0x003513b0  0x0045dc88  Yes         /lib/libc.so.6
0x004a7bb0  0x004b7ce8  Yes         /lib/libselinux.so.1
0x004c0430  0x004c05a8  Yes         /tmp/gfsZ54KNU
0x004c2f50  0x004c4748  Yes         /lib/libgthread-2.0.so.0
0x004c8940  0x004cd088  Yes         /lib/librt.so.1
0x004d51f0  0x004e0b58  No          /lib/libpthread.so.0
(gdb) share
Symbols already loaded for /lib/ld-linux.so.2
Symbols already loaded for /usr/local/lib/libufs2D-0.9.so.2
Symbols already loaded for /usr/local/lib/libgts-0.7.so.5
Symbols already loaded for /lib/libgmodule-2.0.so.0
Symbols already loaded for /lib/libdl.so.2
Symbols already loaded for /lib/libglib-2.0.so.0
Symbols already loaded for /lib/libm.so.6
Symbols already loaded for /lib/libc.so.6
Symbols already loaded for /lib/libselinux.so.1
Symbols already loaded for /tmp/gfsZ54KNU
Symbols already loaded for /lib/libgthread-2.0.so.0
Symbols already loaded for /lib/librt.so.1
Loaded symbols for /lib/libpthread.so.0
(gdb) info share
From        To          Syms Read   Shared Object Library
0x00110810  0x0012724f  Yes         /lib/ld-linux.so.2
0x0013ef00  0x001ca5d8  Yes         /usr/local/lib/libufs2D-0.9.so.2
0x001dfb80  0x00221638  Yes         /usr/local/lib/libgts-0.7.so.5
0x00228c50  0x00229cc8  Yes         /lib/libgmodule-2.0.so.0
0x0022ca60  0x0022da68  Yes         /lib/libdl.so.2
0x002401f0  0x002bf4d8  Yes         /lib/libglib-2.0.so.0
0x00315420  0x0032fe48  Yes         /lib/libm.so.6
0x003513b0  0x0045dc88  Yes         /lib/libc.so.6
0x004a7bb0  0x004b7ce8  Yes         /lib/libselinux.so.1
0x004c0430  0x004c05a8  Yes         /tmp/gfsZ54KNU
0x004c2f50  0x004c4748  Yes         /lib/libgthread-2.0.so.0
0x004c8940  0x004cd088  Yes         /lib/librt.so.1
0x004d51f0  0x004e0b58  Yes         /lib/libpthread.so.0
(gdb) run -T "rho" < UAM10_002_UFS-005000.sim > test.plt
The program being debugged has been started already.
Start it from the beginning? (y or n) y

Starting program: /usr/local/bin/ufs2oogl2D -T "rho" < UAM10_002_UFS-005000.sim > test.plt

Detaching after fork from child process 8775.
[Thread debugging using libthread_db enabled]
Error while reading shared library symbols:
Cannot find new threads: generic error
Cannot find new threads: generic error
(gdb) info share
From        To          Syms Read   Shared Object Library
0x00110810  0x0012724f  Yes         /lib/ld-linux.so.2
0x0013ef00  0x001ca5d8  Yes         /usr/local/lib/libufs2D-0.9.so.2
0x001dfb80  0x00221638  Yes         /usr/local/lib/libgts-0.7.so.5
0x00228c50  0x00229cc8  Yes         /lib/libgmodule-2.0.so.0
0x0022ca60  0x0022da68  Yes         /lib/libdl.so.2
0x002401f0  0x002bf4d8  Yes         /lib/libglib-2.0.so.0
0x00315420  0x0032fe48  Yes         /lib/libm.so.6
0x003513b0  0x0045dc88  Yes         /lib/libc.so.6
0x004a7bb0  0x004b7ce8  Yes         /lib/libselinux.so.1
0x004c0430  0x004c05a8  Yes         /tmp/gfsZ54KNU
0x004c2f50  0x004c4748  Yes         /lib/libgthread-2.0.so.0
0x004c8940  0x004cd088  Yes         /lib/librt.so.1
0x004d51f0  0x004e0b58  No          /lib/libpthread.so.0

Following your example:

I have a fresh out-of-the-box installation of Fedora 9 for x86_64.
Here is what I see:

$ cat t.c
#include <pthread.h>

void *fn(void *p)
{
   char *cp = (char *)p;
   cp[0] = 'a';
   return p;
}

int main()
{
    pthread_t tid;
    pthread_create(&tid, 0, fn, 0);
    pthread_join(tid, 0);
    return 0;
}

$ gcc -g -pthread t.c && gdb ./a.out
GNU gdb Fedora (6.8-1.fc9)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu"...
(gdb) run
Starting program: a.out
[Thread debugging using libthread_db enabled]
[New Thread 0x7ff617b6c6f0 (LWP 2907)]
[New Thread 0x42533950 (LWP 2910)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x42533950 (LWP 2910)]
0x0000000000400590 in fn (p=0x0) at t.c:6
6          cp[0] = 'a';
Missing separate debuginfos, use: debuginfo-install glibc.x86_64
(gdb) info thread
* 2 Thread 0x42533950 (LWP 2910)  0x0000000000400590 in fn (p=0x0) at t.c:6
  1 Thread 0x7ff617b6c6f0 (LWP 2907)  0x0000003c9f807b75 in
pthread_join () from /lib64/libpthread.so.0
(gdb) quit
The program is running.  Exit anyway? (y or n) y

$ rpm -qf /lib64/libpthread.so.0 /lib64/libthread_db.so.1
glibc-2.8-3.x86_64
glibc-2.8-3.x86_64

I did 'debuginfo-install glibc.x86_64' just to check if that makes
any difference... It didn't:

(gdb) run
Starting program: /root/a.out
[Thread debugging using libthread_db enabled]
[New Thread 0x7f7e9e9ce6f0 (LWP 2948)]
[New Thread 0x426f2950 (LWP 2951)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x426f2950 (LWP 2951)]
0x0000000000400590 in fn (p=0x0) at t.c:6
6          cp[0] = 'a';
(gdb) inf thread
* 2 Thread 0x426f2950 (LWP 2951)  0x0000000000400590 in fn (p=0x0) at t.c:6
  1 Thread 0x7f7e9e9ce6f0 (LWP 2948)  0x0000003c9f807b75 in
pthread_join (threadid=<value optimized out>,
    thread_return=<value optimized out>) at pthread_join.c:89
(gdb)

I get essentially the same output.

It looks like something to do with gdb not finding the symbols for /lib/libpthread.so.0. Does this have something to do with ldd not listing libpthread as a shared lib? Or perhaps something with libpthread really being stripped (but file shows otherwise)?

This is quite perplexing, and I would appreciate any help!

Regards,

Andrew L.

Follow-Ups:
- Re: "Cannot find new threads" on Fedora 9, but not on CentOS 5 (?)
  - From: Daniel Jacobowitz
- Re: "Cannot find new threads" on Fedora 9, but not on CentOS 5 (?)
  - From: Paul Pluzhnikov

References:
- "Cannot find new threads" on Fedora 9, but not on CentOS 5 (?)
  - From: Andrew Lofthouse
- Re: "Cannot find new threads" on Fedora 9, but not on CentOS 5 (?)
  - From: Paul Pluzhnikov

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