mprobe(3)

1MCHECK(3)                  Linux Programmer's Manual                 MCHECK(3)
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NAME

6       mcheck,  mcheck_check_all,  mcheck_pedantic,  mprobe - heap consistency
7       checking
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SYNOPSIS

10       #include <mcheck.h>
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12       int mcheck(void (*abortfunc)(enum mcheck_status mstatus));
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14       int mcheck_pedantic(void (*abortfunc)(enum mcheck_status mstatus));
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16       void mcheck_check_all(void);
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18       enum mcheck_status mprobe(void *ptr);
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DESCRIPTION

21       The mcheck() function installs a set of debugging hooks  for  the  mal‐
22       loc(3)  family  of memory-allocation functions.  These hooks cause cer‐
23       tain consistency checks to be performed on the state of the heap.   The
24       checks  can detect application errors such as freeing a block of memory
25       more than once or corrupting the bookkeeping data structures that imme‐
26       diately precede a block of allocated memory.
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28       To  be effective, the mcheck() function must be called before the first
29       call to malloc(3) or a related function.  In cases where this is diffi‐
30       cult  to  ensure, linking the program with -lmcheck inserts an implicit
31       call to mcheck() (with a NULL argument) before the first call to a mem‐
32       ory-allocation function.
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34       The  mcheck_pedantic()  function  is  similar to mcheck(), but performs
35       checks on all allocated blocks whenever one  of  the  memory-allocation
36       functions is called.  This can be very slow!
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38       The  mcheck_check_all() function causes an immediate check on all allo‐
39       cated blocks.  This call  is  effective  only  if  mcheck()  is  called
40       beforehand.
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42       If the system detects an inconsistency in the heap, the caller-supplied
43       function pointed to by abortfunc is invoked  with  a  single  argument,
44       mstatus,  that  indicates  what type of inconsistency was detected.  If
45       abortfunc is NULL, a default function prints an error message on stderr
46       and calls abort(3).
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48       The  mprobe()  function  performs  a  consistency check on the block of
49       allocated memory pointed to by ptr.  The mcheck()  function  should  be
50       called beforehand (otherwise mprobe() returns MCHECK_DISABLED).
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52       The  following list describes the values returned by mprobe() or passed
53       as the mstatus argument when abortfunc is invoked:
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55       MCHECK_DISABLED (mprobe() only)
56              mcheck() was not called before the first memory allocation func‐
57              tion was called.  Consistency checking is not possible.
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59       MCHECK_OK (mprobe() only)
60              No inconsistency detected.
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62       MCHECK_HEAD
63              Memory preceding an allocated block was clobbered.
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65       MCHECK_TAIL
66              Memory following an allocated block was clobbered.
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68       MCHECK_FREE
69              A block of memory was freed twice.
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RETURN VALUE

72       mcheck() and mcheck_pedantic() return 0 on success, or -1 on error.
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VERSIONS

75       The  mcheck_pedantic()  and  mcheck_check_all() functions are available
76       since glibc 2.2.  The mcheck() and mprobe() functions are present since
77       at least glibc 2.0
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ATTRIBUTES

80       For   an   explanation   of   the  terms  used  in  this  section,  see
81       attributes(7).
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83       ┌─────────────────────────────┬───────────────┬───────────────────────┐
84       │Interface                    │ Attribute     │ Value                 │
85       ├─────────────────────────────┼───────────────┼───────────────────────┤
86       │mcheck(), mcheck_pedantic(), │ Thread safety │ MT-Unsafe race:mcheck │
87       │mcheck_check_all(), mprobe() │               │ const:malloc_hooks    │
88       └─────────────────────────────┴───────────────┴───────────────────────┘
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CONFORMING TO

91       These functions are GNU extensions.
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NOTES

94       Linking a program with -lmcheck and using the MALLOC_CHECK_ environment
95       variable (described in mallopt(3)) cause the same kinds of errors to be
96       detected.  But, using MALLOC_CHECK_ does not require the application to
97       be relinked.
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EXAMPLE

100       The  program  below  calls mcheck() with a NULL argument and then frees
101       the same block of memory twice.  The  following  shell  session  demon‐
102       strates what happens when running the program:
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104           $ ./a.out
105           About to free
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107           About to free a second time
108           block freed twice
109           Aborted (core dumped)
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111   Program source
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113       #include <stdlib.h>
114       #include <stdio.h>
115       #include <mcheck.h>
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117       int
118       main(int argc, char *argv[])
119       {
120           char *p;
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122           if (mcheck(NULL) != 0) {
123               fprintf(stderr, "mcheck() failed\n");
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125               exit(EXIT_FAILURE);
126           }
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128           p = malloc(1000);
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130           fprintf(stderr, "About to free\n");
131           free(p);
132           fprintf(stderr, "\nAbout to free a second time\n");
133           free(p);
134
135           exit(EXIT_SUCCESS);
136       }
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COLOPHON

142       This  page  is  part of release 4.16 of the Linux man-pages project.  A
143       description of the project, information about reporting bugs,  and  the
144       latest     version     of     this    page,    can    be    found    at
145       https://www.kernel.org/doc/man-pages/.
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149GNU                               2017-09-15                         MCHECK(3)