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mcheck(3) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ATTRIBUTES \|STANDARDS \|HISTORY \|NOTES \|EXAMPLES \|SEE ALSO \|COLOPHON

mcheck(3)                Library Functions Manualmcheck(3)

NAME top

       mcheck, mcheck_check_all, mcheck_pedantic, mprobe - heap       consistency checking

LIBRARY top

       Standard C library (libc,-lc)

SYNOPSIS top

#include <mcheck.h>int mcheck(typeof(void (enum mcheck_statusmstatus)) *f);int mcheck_pedantic(typeof(void (enum mcheck_statusmstatus)) *f);void mcheck_check_all(void);enum mcheck_status mprobe(void *ptr);

DESCRIPTION top

       Themcheck() function installs a set of debugging hooks for themalloc(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, themcheck() function must be called before the       first call tomalloc(3) or a related function.  In cases where       this is difficult to ensure, linking the program with-lmcheck       inserts an implicit call tomcheck() (with a NULL argument) before       the first call to a memory-allocation function.       Themcheck_pedantic() function is similar tomcheck(), but       performs checks on all allocated blocks whenever one of the       memory-allocation functions is called.  This can be very slow!       Themcheck_check_all() function causes an immediate check on all       allocated blocks.  This call is effective only ifmcheck() is       called beforehand.       If the system detects an inconsistency in the heap, the caller-       supplied function pointed to byf is invoked with a single       argument,mstatus, that indicates what type of inconsistency was       detected.  Iff is NULL, a default function prints an error       message onstderr and callsabort(3).       Themprobe() function performs a consistency check on the block of       allocated memory pointed to byptr.  Themcheck() function should       be called beforehand (otherwisemprobe() returnsMCHECK_DISABLED).       The following list describes the values returned bymprobe() or       passed as themstatus argument whenf 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.

RETURN VALUE top

mcheck() andmcheck_pedantic() return 0 on success, or -1 on       error.

ATTRIBUTES top

       For an explanation of the terms used in this section, seeattributes(7).       ┌───────────────────────────┬───────────────┬────────────────────┐       │Interface│Attribute│Value│       ├───────────────────────────┼───────────────┼────────────────────┤       │mcheck(),                 │ Thread safety │ MT-Unsafe          │       │mcheck_pedantic(),        │               │ race:mcheck        │       │mcheck_check_all(),       │               │ const:malloc_hooks │       │mprobe()                  │               │                    │       └───────────────────────────┴───────────────┴────────────────────┘

STANDARDS top

       GNU.

HISTORY top

mcheck_pedantic()mcheck_check_all()              glibc 2.2.mcheck()mprobe()              glibc 2.0.

NOTES top

       Linking a program with-lmcheck and using theMALLOC_CHECK_       environment variable (described inmallopt(3)) cause the same       kinds of errors to be detected.  But, usingMALLOC_CHECK_does not       require the application to be relinked.

EXAMPLES top

       The program below callsmcheck() 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);       }

COLOPHON top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-06-05mcheck(3)

Pages that refer to this page:malloc(3), malloc_hook(3), mallopt(3), mtrace(3)

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