CODEWITHSUNDEEP
linuxmultithreadinggdb
Bloodmoon
Bloodmoon

Reputation: 1348

Debug multi-thread program (openmp) using GDB

all

I am tring to use gdb to debug a program with 24 threads in Fedora, and I have the following output of GDB. When I want to switch to the specific thread that a segmentation fault happens, I cannot switch to that thread with the thread command (last 4 lines in the GDB output). Could you please help me with it? And do you know what error it is? The GDB output is as follows:

    [root@localhost nameComponentEncoding]# gdb NCE_david
GNU gdb (GDB) Fedora (7.2.90.20110429-36.fc15)
Copyright (C) 2011 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".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /mnt/disk2/experiments_BLOODMOON/two_stage_bloom_filter/programs/nameComponentEncoding/NCE_david
(gdb) r 
Starting program: 
[Thread debugging using libthread_db enabled]

[New Thread 0x7fffd2bf5700 (LWP 11538)]
[New Thread 0x7fffd23f4700 (LWP 11539)]
[New Thread 0x7fffd1bf3700 (LWP 11540)]
[New Thread 0x7fffd13f2700 (LWP 11541)]
[New Thread 0x7fffd0bf1700 (LWP 11542)]
[New Thread 0x7fffd03f0700 (LWP 11543)]
[New Thread 0x7fffcfbef700 (LWP 11544)]
[New Thread 0x7fffcf3ee700 (LWP 11545)]
[New Thread 0x7fffcebed700 (LWP 11546)]
[New Thread 0x7fffce3ec700 (LWP 11547)]
[New Thread 0x7fffcdbeb700 (LWP 11548)]
[New Thread 0x7fffcd3ea700 (LWP 11549)]
[New Thread 0x7fffccbe9700 (LWP 11550)]
[New Thread 0x7fffcc3e8700 (LWP 11551)]
[New Thread 0x7fffcbbe7700 (LWP 11552)]
[New Thread 0x7fffcb3e6700 (LWP 11553)]
[New Thread 0x7fffcabe5700 (LWP 11554)]
[New Thread 0x7fffca3e4700 (LWP 11555)]
[New Thread 0x7fffc9be3700 (LWP 11556)]
[New Thread 0x7fffc93e2700 (LWP 11557)]
[New Thread 0x7fffc8be1700 (LWP 11558)]
[New Thread 0x7fffc83e0700 (LWP 11559)]
[New Thread 0x7fffc7bdf700 (LWP 11560)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffd2bf5700 (LWP 11538)]
compare (__str="art", this=0xbf934d0) at /usr/lib/gcc/x86_64-redhat-linux/4.6.0/
2175            const size_type __size = this->size();
(gdb) thread 11538
Thread ID 11538 not known.
(gdb) thread 0x7fffd2bf5700
Thread ID -759212288 not known.

Upvotes: 3

Views: 5021

Answers (1)

scottt
scottt

Reputation: 7228

GDB has its own numbering for threads. Do something like:

(gdb) info threads

  Id   Target Id         Frame 
  <... snip ...>
  2    Thread 0x7ffff7fc1700 (LWP 11538) ...
* 1    Thread 0x7ffff7fc2740 (LWP 11537) ...
# thread with PID 11538 is GDB thread number 2
(gdb) thread 2

From

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffd2bf5700 (LWP 11538)]
compare (__str="art", this=0xbf934d0) at /usr/lib/gcc/x86_64-redhat-linux/4.6.0/
2175            const size_type __size = this->size();

It does seem that the segfault is caused by thread 11538. Using pthread_setname_np() to name your threads would make debugging in GDB easier.

My guess would be that this, the C++ instance variable, was NULL at that point (easily verifiable) and your case is a "use after free" error.

Upvotes: 5

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