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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO |
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mcheck(3) Library Functions Manual mcheck(3)
mcheck, mcheck_check_all, mcheck_pedantic, mprobe - heap
consistency checking
Standard C library (libc, -lc)
#include <mcheck.h>
int mcheck(void (*abortfunc)(enum mcheck_status mstatus));
int mcheck_pedantic(void (*abortfunc)(enum mcheck_status mstatus));
void mcheck_check_all(void);
enum mcheck_status mprobe(void *ptr);
The mcheck() function installs a set of debugging hooks for the
malloc(3) family of memory-allocation functions. These hooks
cause certain consistency checks to be performed on the state of
the heap. The checks can detect application errors such as
freeing a block of memory more than once or corrupting the
bookkeeping data structures that immediately precede a block of
allocated memory.
To be effective, the mcheck() function must be called before the
first call to malloc(3) or a related function. In cases where
this is difficult to ensure, linking the program with -lmcheck
inserts an implicit call to mcheck() (with a NULL argument)
before the first call to a memory-allocation function.
The mcheck_pedantic() function is similar to mcheck(), but
performs checks on all allocated blocks whenever one of the
memory-allocation functions is called. This can be very slow!
The mcheck_check_all() function causes an immediate check on all
allocated blocks. This call is effective only if mcheck() is
called beforehand.
If the system detects an inconsistency in the heap, the caller-
supplied function pointed to by abortfunc is invoked with a
single argument, mstatus, that indicates what type of
inconsistency was detected. If abortfunc is NULL, a default
function prints an error message on stderr and calls abort(3).
The mprobe() function performs a consistency check on the block
of allocated memory pointed to by ptr. The mcheck() function
should be called beforehand (otherwise mprobe() returns
MCHECK_DISABLED).
The following list describes the values returned by mprobe() or
passed as the mstatus argument when abortfunc is invoked:
MCHECK_DISABLED (mprobe() only)
mcheck() was not called before the first memory allocation
function was called. Consistency checking is not
possible.
MCHECK_OK (mprobe() only)
No inconsistency detected.
MCHECK_HEAD
Memory preceding an allocated block was clobbered.
MCHECK_TAIL
Memory following an allocated block was clobbered.
MCHECK_FREE
A block of memory was freed twice.
mcheck() and mcheck_pedantic() return 0 on success, or -1 on
error.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────────┬───────────────┬────────────────────┐
│Interface │ Attribute │ Value │
├───────────────────────────┼───────────────┼────────────────────┤
│mcheck(), │ Thread safety │ MT-Unsafe │
│mcheck_pedantic(), │ │ race:mcheck │
│mcheck_check_all(), │ │ const:malloc_hooks │
│mprobe() │ │ │
└───────────────────────────┴───────────────┴────────────────────┘
GNU.
mcheck_pedantic()
mcheck_check_all()
glibc 2.2.
mcheck()
mprobe()
glibc 2.0.
Linking a program with -lmcheck and using the MALLOC_CHECK_
environment variable (described in mallopt(3)) cause the same
kinds of errors to be detected. But, using MALLOC_CHECK_ does
not require the application to be relinked.
The program below calls mcheck() with a NULL argument and then
frees the same block of memory twice. The following shell
session demonstrates what happens when running the program:
$ ./a.out
About to free
About to free a second time
block freed twice
Aborted (core dumped)
Program source
#include <mcheck.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
char *p;
if (mcheck(NULL) != 0) {
fprintf(stderr, "mcheck() failed\n");
exit(EXIT_FAILURE);
}
p = malloc(1000);
fprintf(stderr, "About to free\n");
free(p);
fprintf(stderr, "\nAbout to free a second time\n");
free(p);
exit(EXIT_SUCCESS);
}
malloc(3), mallopt(3), mtrace(3)
Linux man-pages 6.04 2023-03-30 mcheck(3)
Pages that refer to this page: malloc(3), malloc_hook(3), mallopt(3), mtrace(3)
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HTML rendering created 2023-06-24 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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