NAME
mcheck, mcheckcheckall, mcheckpedantic, mprobe - heap consistency checking SYNOPSIS
#include
int mcheck(void (*abortfunc)(enum mcheckstatus mstatus)); int mcheckpedantic(void (*abortfunc)(enum mcheckstatus mstatus)); void mcheckcheckall(void); enum mcheckstatus mprobe(void *ptr); DESCRIPTION The mcheck() function installs a set of debugging hooks for the mal‐ loc(3) family of memory-allocation functions. These hooks cause cer‐ tain 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 imme‐ diately 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 diffi‐
cult to ensure, linking the program with -mcheck inserts an implicit call to mcheck() (with a NULL argument) before the first call to a mem‐
ory-allocation function. The mcheckpedantic() 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 mcheckcheckall() function causes an immediate check on all allo‐ cated 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 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 MCHECKDISABLED). The following list describes the values returned by mprobe() or passed as the mstatus argument when abortfunc is invoked: MCHECKDISABLED (mprobe() only) mcheck() was not called before the first memory allocation func‐ tion was called. Consistency checking is not possible. MCHECKOK (mprobe() only) No inconsistency detected. MCHECKHEAD Memory preceding an allocated block was clobbered. MCHECKTAIL Memory following an allocated block was clobbered. MCHECKFREE A block of memory was freed twice. RETURN VALUE
mcheck() and mcheckpedantic() return 0 on success, or -1 on error. VERSIONS The mcheckpedantic() and mcheckcheckall() functions are available since glibc 2.2. The mcheck() and mprobe() functions are present since at least glibc 2.0 CONFORMING TO These functions are GNU extensions. NOTES
Linking a program with -lmcheck and using the MALLOCCHECK environment variable (described in mallopt(3)) cause the same kinds of errors to be detected. But, using MALLOCCHECK does not require the application to be relinked. EXAMPLE The program below calls mcheck() with a NULL argument and then frees the same block of memory twice. The following shell session demon‐ strates 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
#include
#include
int main(int argc, char *argv[]) { char *p; if (mcheck(NULL) != 0) { fprintf(stderr, "mcheck() failed\n"); exit(EXITFAILURE); } p = malloc(1000); fprintf(stderr, "About to free\n"); free(p); fprintf(stderr, "\nAbout to free a second time\n"); free(p); exit(EXITSUCCESS); } SEE ALSO malloc(3), mallopt(3), mtrace(3) COLOPHON This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2012-04-18 MCHECK(3)