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mcheck.3: New man page for mcheck(3) and related functions
Also describes mcheck_check_all(3) mcheck_pedantic(3), and mprobe(3) Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH MCHECK 3 2012-04-18 "GNU" "Linux Programmer's Manual"
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.SH NAME
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mcheck, mcheck_check_all, mcheck_pedantic, mprobe - heap consistency checking
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.SH SYNOPSIS
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.nf
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.B #include <mcheck.h>
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.sp
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.BI "int mcheck(void (*" abortfunc ")(enum mcheck_status " mstatus ));
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.BI "int mcheck_pedantic(void (*" abortfunc ")(enum mcheck_status " mstatus ));
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.B void mcheck_check_all(void);
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.BI "enum mcheck_status mprobe(void *" ptr );
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.fi
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.SH DESCRIPTION
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The
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.BR mcheck ()
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function installs a set of debugging hooks for the
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.BR malloc (3)
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family of memory-allocation functions.
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These hooks cause certain consistency checks to be performed
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on the state of the heap.
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The checks can detect application errors such as freeing a block of memory
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more than once or corrupting the bookkeeping data structures
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that immediately precede a block of allocated memory.
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To be effective, the
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.BR mcheck ()
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function must be called before the first call to
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.BR malloc (3)
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or a related function.
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In cases where this is difficult to ensure, linking the program with
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.IR \-mcheck
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inserts an implicit call to
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.BR mcheck ()
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(with a NULL argument)
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before the first call to a memory-allocation function.
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The
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.BR mcheck_pedantic ()
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function is similar to
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.BR mcheck (),
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but performs checks on all allocated blocks whenever
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one of the memory-allocation functions is called.
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This can be very slow!
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The
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.BR mcheck_check_all ()
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function causes an immediate check on all allocated blocks.
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This call is only effective if
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.BR mcheck ()
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is called beforehand.
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If the system detects an inconsistency in the heap,
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the caller-supplied function pointed to by
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.I abortfunc
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is invoked with a single argument argument,
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.IR mstatus ,
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that indicates what type of inconsistency was detected.
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If
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.I abortfunc
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is NULL, a default function prints an error message on
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.IR stderr
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and calls
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.BR abort (3).
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The
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.BR mprobe ()
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function performs a consistency check on
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the block of allocated memory pointed to by
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.IR ptr .
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The
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.BR mcheck ()
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function should be called beforehand (otherwise
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.BR mprobe ()
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returns
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.BR MCHECK_DISABLED ).
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The following list describes the values returned by
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.BR mprobe ()
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or passed as the
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.I mstatus
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argument when
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.I abortfunc
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is invoked:
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.TP
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.BR MCHECK_DISABLED " (" mprobe "() only)"
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.BR mcheck ()
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was not called before the first memory allocation function was called.
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Consistency checking is not possible.
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.TP
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.BR MCHECK_OK " (" mprobe "() only)"
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No inconsistency detected.
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.TP
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.B MCHECK_HEAD
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Memory preceding an allocated block was clobbered.
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.TP
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.B MCHECK_TAIL
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Memory following an allocated block was clobbered.
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.TP
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.B
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MCHECK_FREE
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A block of memory was freed twice.
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.SH RETURN VALUE
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.BR mcheck ()
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and
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.BR mcheck_pedantic ()
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return 0 on success, or \-1 on error.
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.SH VERSIONS
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The
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.BR mcheck_pedantic ()
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and
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.BR mcheck_check_all ()
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functions are available since glibc 2.2.
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The
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.BR mcheck()
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and
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.BR mprobe()
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functions are present since at least glibc 2.0
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.SH CONFORMING TO
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These functions are GNU extensions.
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.SH NOTES
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Linking a program with
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.I \-lmcheck
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and using the
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.B MALLOC_CHECK_
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environment variable (described in
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.BR mallopt (3))
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cause the same kinds of errors to be detected.
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But, using
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.B MALLOC_CHECK_
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does not require the application to be relinked.
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.\" But is MALLOC_CHECK_ slower?
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.SH EXAMPLE
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The program below calls
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.BR mcheck ()
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with a NULL argument and then frees the same block of memory twice.
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The following shell session demonstrates what happens
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when running the program:
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.in +4n
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.nf
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.RB "$" " ./a.out"
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About to free
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About to free a second time
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block freed twice
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Aborted (core dumped)
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.fi
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.in
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.SS Program source
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\&
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.nf
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#include <stdlib.h>
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#include <stdio.h>
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#include <mcheck.h>
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int
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main(int argc, char *argv[])
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{
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char *p;
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if (mcheck(NULL) != 0) {
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fprintf(stderr, "mcheck() failed\\n");
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exit(EXIT_FAILURE);
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}
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p = malloc(1000);
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fprintf(stderr, "About to free\\n");
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free(p);
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fprintf(stderr, "\\nAbout to free a second time\\n");
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free(p);
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH SEE ALSO
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.BR malloc (3),
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.\" FIXME add SEE ALSO pointer from malloc(3) to here
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.\" FIXME add SEE ALSO pointer from mallopt(3) to here
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.\" FIXME add SEE ALSO pointer from mtrace(3) to here
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.BR mallopt (3),
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.BR mtrace (3)
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