How to use libumem to find a bad free call
Thoughts on developer tools.

All | Dbx | Development Tools | Life in General | OpenSolaris | plus | Software Philosophy | Sun Studio

fav comics

« Reporting bugs | Main | Conform »
20060322 Wednesday March 22, 2006

How to use libumem to find a bad free call I have not seen any good simple tutorials on how to use libumem for debugging.  (Unless you also want to learn how to use mdb).  So I wrote a simple example.

% more t.c

#include 
#include 
int main()
{
    int i;
    free(&i);
    i = 10;
    char * p = (char *) malloc(1000);
}

This program has a bug, and it might crash or it might not. It might crash right away, or it might crash after running longer (if it had more code after the bug). Using libumem with default options, will cause more basic assertion checking.

% cc -g t.c
% a.out
% # notice no crash
% LD_PRELOAD=/lib/libumem.so ./a.out
Abort (core dumped)
% dbx -c 'where;quit' - core
Corefile specified executable: "/home/quenelle/./a.out"
Reading a.out
core file header read successfully
Reading ld.so.1
Reading libumem.so.1
Reading libc.so.1
Reading libc_psr.so.1
program terminated by signal ABRT (Abort)
0xff2c0f90: __lwp_kill+0x0008:  bcc,a,pt  %icc,__lwp_kill+0x18  ! 0xff2c0fa0
Current function is main
    8       free(&i);
  [1] __lwp_kill(0x0, 0x6, 0x0, 0x0, 0x0, 0x0), at 0xff2c0f90
  [2] raise(0x6, 0x0, 0x20f90, 0xff36b7cc, 0xff38a000, 0xff38abc4), at 0xff25fd78
  [3] umem_do_abort(0x4, 0xffbfe6c0, 0x6, 0x20ecc, 0xff37680c, 0x0), at 0xff3690fc
  [4] umem_err_recoverable(0xff377818, 0xa, 0x20dc4, 0xff38a6fc, 0xff38d0d0, 0xff377823), at 0xff3692a0
  [5] process_free(0xffbfe9d8, 0x1, 0x0, 0x3e3a1000, 0x1ee5c, 0x20c28), at 0xff36b2b0
=>[6] main(), line 8 in "t.c"

Abort (core dumped)

This trick can often be used to find the place where your malloc/free bug happened.  There are some environment variables you can use to control the behavior of libumem. You can read more about them in the umem_debug man page.  You can also find out more about libumem by reading the various white papers that are available.  You do a google search on "libumem" or "libumem solaris" to find out more.

Posted by Chris Quenelle ( Mar 22 2006, 04:53:07 PM PST ) - Permalink - Comments [2] -

Comments:

You didn't read the man page very carefully. It points you to umem_debug(3malloc) which has a lot of useful information.

Posted by 192.18.43.5 on March 22, 2006 at 10:01 PM PST #

You are correct, I'll update my blog entry.

Posted by Chris Quenelle on March 23, 2006 at 01:01 PM PST #

Post a Comment:

Comments are closed for this entry.

Older blog entries:

mug shot Chris Quenelle is a tools developer at Sun Microsystems. He's worked on performance and debugging tools at Sun for more than 10 years. He reads comic books and science fiction, and has more tivos than he can keep track of.

Calendar

« November 2009
SunMonTueWedThuFriSat
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
     
       
Today

RSS Feeds

XML
All
/Dbx
/Development Tools
/Life in General
/OpenSolaris
/plus
/Software Philosophy
/Sun Studio

Search

Links

Navigation

Referers

Today's Page Hits: 76