mprobe(3)

1mcheck(3)                  Library Functions Manual                  mcheck(3)
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NAME

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

10       Standard C library (libc, -lc)
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SYNOPSIS

13       #include <mcheck.h>
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15       int mcheck(void (*abortfunc)(enum mcheck_status mstatus));
16       int mcheck_pedantic(void (*abortfunc)(enum mcheck_status mstatus));
17       void mcheck_check_all(void);
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19       enum mcheck_status mprobe(void *ptr);
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DESCRIPTION

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

73       mcheck() and mcheck_pedantic() return 0 on success, or -1 on error.
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ATTRIBUTES

76       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
77       tributes(7).
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79       ┌─────────────────────────────────┬───────────────┬────────────────────┐
80       │Interface                        │ Attribute     │ Value              │
81       ├─────────────────────────────────┼───────────────┼────────────────────┤
82       │mcheck(), mcheck_pedantic(),     │ Thread safety │ MT-Unsafe          │
83       │mcheck_check_all(), mprobe()     │               │ race:mcheck        │
84       │                                 │               │ const:malloc_hooks │
85       └─────────────────────────────────┴───────────────┴────────────────────┘
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STANDARDS

88       GNU.
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HISTORY

91       mcheck_pedantic()
92       mcheck_check_all()
93              glibc 2.2.
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95       mcheck()
96       mprobe()
97              glibc 2.0.
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NOTES

100       Linking a program with -lmcheck and using the MALLOC_CHECK_ environment
101       variable (described in mallopt(3)) cause the same kinds of errors to be
102       detected.  But, using MALLOC_CHECK_ does not require the application to
103       be relinked.
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EXAMPLES

106       The program below calls mcheck() with a NULL argument  and  then  frees
107       the  same  block  of  memory twice.  The following shell session demon‐
108       strates what happens when running the program:
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110           $ ./a.out
111           About to free
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113           About to free a second time
114           block freed twice
115           Aborted (core dumped)
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117   Program source
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119       #include <mcheck.h>
120       #include <stdio.h>
121       #include <stdlib.h>
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123       int
124       main(void)
125       {
126           char *p;
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128           if (mcheck(NULL) != 0) {
129               fprintf(stderr, "mcheck() failed\n");
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131               exit(EXIT_FAILURE);
132           }
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134           p = malloc(1000);
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136           fprintf(stderr, "About to free\n");
137           free(p);
138           fprintf(stderr, "\nAbout to free a second time\n");
139           free(p);
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141           exit(EXIT_SUCCESS);
142       }
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