The GNU checker package has been decommissioned, as valgrind does a better job and is being actively maintained. Old home page preserved below for archeologists.
Checker is a tool which finds memory errors at runtime. Its primary function is to emit a warning when the program reads an uninitialized variable or memory area, or when the program accesses an unallocated memory area.
The Malloc library of Checker is very robust, though a bit slower than the usual GNU Malloc. Checker issues warnings when:
free
or realloc
is called with a
pointer that has not been obtained from malloc
,
calloc
, or realloc
.
free
or realloc
is called with a
pointer that has been previously freed.
Checker's Malloc will refrain from reusing a freed block immediately; reuse of the block is delayed for some additional number of calls to free. This is to catch accesses to the block shortly after it has been freed.
Checker implements a garbage detector that can be called either in
your program, by a debugger such as GDB, or on exit from the program.
The garbage detector displays all the memory leaks along with the
functions that called malloc
.
example.c
:
#include <stdlib.h> int main () { char *zone = malloc (20); char *ptr = NULL; int i; char c; c = zone[1]; /* error: read an uninitialized char */ c = zone[-2]; /* error: read before the zone */ zone[25] = ' '; /* error: write after the zone */ *ptr = 2; /* error: use a NULL pointer, must produce a core */ }To compile this example with Checker, simply use
checkergcc
instead of gcc
:
% checkergcc -o example example.cNext, to run the example:
% ./exampleExecution produces these warnings:
Checker 0.9 (sparc-sun-solaris2.5.1) Copyright (C) 1998 Tristan Gingold. Checker is a memory access detector. Checker is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. For more information, set CHECKEROPTS to `--help' From Checker (pid:04713): `./example' is running (Sun Jan 18 14:56:49 1998) From Checker (pid:04713): (ruh) read uninitialized byte(s) in a block. When Reading 1 byte(s) at address 0x000398a1, inside the heap (sbrk). 1 bytes into a block (start: 0x398a0, length: 20, mdesc: 0x0). The block was allocated from: pc=0x00022f1c in chkr_malloc at ../stubs/stubs-malloc.c:51 pc=0x0001339c in main at ../example.c:7 pc=0x000155f0 in startup at ../config/sparc/solaris2/startup.c:148 pc=0x00013298 in *unknown* at *unknown*:0 Stack frames are: pc=0x000133f4 in main at ../example.c:12 pc=0x000155f0 in startup at ../config/sparc/solaris2/startup.c:148 pc=0x00013298 in *unknown* at *unknown*:0 From Checker (pid:04713): (bvh) block bounds violation in the heap. When Reading 1 byte(s) at address 0x0003989e, inside the heap (sbrk). 2 bytes before a block (start: 0x398a0, length: 20, mdesc: 0x0). The block was allocated from: pc=0x00022f1c in chkr_malloc at ../stubs/stubs-malloc.c:51 pc=0x0001339c in main at ../example.c:7 pc=0x000155f0 in startup at ../config/sparc/solaris2/startup.c:148 pc=0x00013298 in *unknown* at *unknown*:0 Stack frames are: pc=0x00013434 in main at ../example.c:13 pc=0x000155f0 in startup at ../config/sparc/solaris2/startup.c:148 pc=0x00013298 in *unknown* at *unknown*:0 From Checker (pid:04713): (bvh) block bounds violation in the heap. When Writing 1 byte(s) at address 0x000398b9, inside the heap (sbrk). 5 bytes after a block (start: 0x398a0, length: 20, mdesc: 0x0). The block was allocated from: pc=0x00022f1c in chkr_malloc at ../stubs/stubs-malloc.c:51 pc=0x0001339c in main at ../example.c:7 pc=0x000155f0 in startup at ../config/sparc/solaris2/startup.c:148 pc=0x00013298 in *unknown* at *unknown*:0 Stack frames are: pc=0x0001345c in main at ../example.c:14 pc=0x000155f0 in startup at ../config/sparc/solaris2/startup.c:148 pc=0x00013298 in *unknown* at *unknown*:0 From Checker (pid:04713): (nza) null zone addressed. When Writing 1 byte(s) at address 0x00000000, inside the NULL zone. You probably deferenced a null pointer. THIS SHOULD CAUSE A SEGMENTATION FAULT. Stack frames are: pc=0x0001347c in main at ../example.c:15 pc=0x000155f0 in startup at ../config/sparc/solaris2/startup.c:148 pc=0x00013298 in *unknown* at *unknown*:0 From Checker (pid:04713): (sig) signal. Receive signal 11 (SEGV): (default action: terminate core ). Segmentation fault
gcc-2.8.1
to use Checker.
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Updated: 11 Dec 1999 jonas