Debugging Dynamic Memory Usage Errors Using HP WDB (5900-1474; WDB 6.2; January 2011)

Example 18 Detecting the location of memory leak

To detect the location of the first leak, follow the steps mentioned below:

a. Execute the program under gdb with memory leak detection option using the

command shown below:

$ gdb -leaks memLeak

HP gdb 6.0.3 for HP Itanium (32 or 64 bit) and target HP-UX 11iv2 and 11iv3.

Hewlett-Packard Wildebeest 6.0.3 (based on GDB) is covered by the

GNU General Public License. Type "show copying" to see the conditions to

change it and/or distribute copies. Type "show warranty" for

warranty/support.

b. Insert a break at the function that allocates the memory.

In this case, the function allocateMemory() allocates the memory.

NOTE: Enter the same input given to the program while executing the program

in batch mode. In this case it is 25.

(gdb) b allocateMemory

Breakpoint 1 at 0x4000ce0:2: file memLeak.c, line 8 from /tmp/memLeak.

(gdb) run

Starting program: /tmp/memLeak

Enter length of string 1

Breakpoint 1, allocateMemory (n=20) at memLeak.c:8

8 void *memBlock = NULL;

(gdb)

c. Step into the calling function and trace the behavior of the pointer pointing to

the allocated memory i.e. step into the createHeader() and collect leak

information with the info leaks command when the execution reaches this

function.

NOTE: The leak information is not reported because the allocateMemory()

function has returned the pointer to the createHeader(). The headerString

is pointing to the allocated memory of size 20.

(gdb) finish

Run till exit from #0 allocateMemory (n=20) at memLeak.c:8

Allocating memory of size 20

0x4000e70:0 in createHeader () at memLeak.c:24

24 char *headerString = (char *) allocateMemory(20);

Value returned is $1= (void *) 0x400124a0

(gdb) info leak

Scanning for memory leaks...

No new leaks.

(gdb)