man3/mcheck.3

   1 .\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
   2 .\"
   3 .\" %%%LICENSE_START(VERBATIM)
   4 .\" Permission is granted to make and distribute verbatim copies of this
   5 .\" manual provided the copyright notice and this permission notice are
   6 .\" preserved on all copies.
   7 .\"
   8 .\" Permission is granted to copy and distribute modified versions of this
   9 .\" manual under the conditions for verbatim copying, provided that the
  10 .\" entire resulting derived work is distributed under the terms of a
  11 .\" permission notice identical to this one.
  12 .\"
  13 .\" Since the Linux kernel and libraries are constantly changing, this
  14 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  15 .\" responsibility for errors or omissions, or for damages resulting from
  16 .\" the use of the information contained herein.  The author(s) may not
  17 .\" have taken the same level of care in the production of this manual,
  18 .\" which is licensed free of charge, as they might when working
  19 .\" professionally.
  20 .\"
  21 .\" Formatted or processed versions of this manual, if unaccompanied by
  22 .\" the source, must acknowledge the copyright and authors of this work.
  23 .\" %%%LICENSE_END
  24 .\"
  25 .TH MCHECK 3  2019-03-06 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 mcheck, mcheck_check_all, mcheck_pedantic, mprobe \- heap consistency checking
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <mcheck.h>
  31 .PP
  32 .BI "int mcheck(void (*" abortfunc ")(enum mcheck_status " mstatus ));
  33 .PP
  34 .BI "int mcheck_pedantic(void (*" abortfunc ")(enum mcheck_status " mstatus ));
  35 .PP
  36 .B void mcheck_check_all(void);
  37 .PP
  38 .BI "enum mcheck_status mprobe(void *" ptr );
  39 .fi
  40 .SH DESCRIPTION
  41 The
  42 .BR mcheck ()
  43 function installs a set of debugging hooks for the
  44 .BR malloc (3)
  45 family of memory-allocation functions.
  46 These hooks cause certain consistency checks to be performed
  47 on the state of the heap.
  48 The checks can detect application errors such as freeing a block of memory
  49 more than once or corrupting the bookkeeping data structures
  50 that immediately precede a block of allocated memory.
  51 .PP
  52 To be effective, the
  53 .BR mcheck ()
  54 function must be called before the first call to
  55 .BR malloc (3)
  56 or a related function.
  57 In cases where this is difficult to ensure, linking the program with
  58 .IR \-lmcheck
  59 inserts an implicit call to
  60 .BR mcheck ()
  61 (with a NULL argument)
  62 before the first call to a memory-allocation function.
  63 .PP
  64 The
  65 .BR mcheck_pedantic ()
  66 function is similar to
  67 .BR mcheck (),
  68 but performs checks on all allocated blocks whenever
  69 one of the memory-allocation functions is called.
  70 This can be very slow!
  71 .PP
  72 The
  73 .BR mcheck_check_all ()
  74 function causes an immediate check on all allocated blocks.
  75 This call is effective only if
  76 .BR mcheck ()
  77 is called beforehand.
  78 .PP
  79 If the system detects an inconsistency in the heap,
  80 the caller-supplied function pointed to by
  81 .I abortfunc
  82 is invoked with a single argument,
  83 .IR mstatus ,
  84 that indicates what type of inconsistency was detected.
  85 If
  86 .I abortfunc
  87 is NULL, a default function prints an error message on
  88 .IR stderr
  89 and calls
  90 .BR abort (3).
  91 .PP
  92 The
  93 .BR mprobe ()
  94 function performs a consistency check on
  95 the block of allocated memory pointed to by
  96 .IR ptr .
  97 The
  98 .BR mcheck ()
  99 function should be called beforehand (otherwise
 100 .BR mprobe ()
 101 returns
 102 .BR MCHECK_DISABLED ).
 103 .PP
 104 The following list describes the values returned by
 105 .BR mprobe ()
 106 or passed as the
 107 .I mstatus
 108 argument when
 109 .I abortfunc
 110 is invoked:
 111 .TP
 112 .BR MCHECK_DISABLED " (" mprobe "() only)"
 113 .BR mcheck ()
 114 was not called before the first memory allocation function was called.
 115 Consistency checking is not possible.
 116 .TP
 117 .BR MCHECK_OK " (" mprobe "() only)"
 118 No inconsistency detected.
 119 .TP
 120 .B MCHECK_HEAD
 121 Memory preceding an allocated block was clobbered.
 122 .TP
 123 .B MCHECK_TAIL
 124 Memory following an allocated block was clobbered.
 125 .TP
 126 .B
 127 MCHECK_FREE
 128 A block of memory was freed twice.
 129 .SH RETURN VALUE
 130 .BR mcheck ()
 131 and
 132 .BR mcheck_pedantic ()
 133 return 0 on success, or \-1 on error.
 134 .SH VERSIONS
 135 The
 136 .BR mcheck_pedantic ()
 137 and
 138 .BR mcheck_check_all ()
 139 functions are available since glibc 2.2.
 140 The
 141 .BR mcheck ()
 142 and
 143 .BR mprobe ()
 144 functions are present since at least glibc 2.0
 145 .SH ATTRIBUTES
 146 For an explanation of the terms used in this section, see
 147 .BR attributes (7).
 148 .TS
 149 allbox;
 150 lbw28 lb lbw21
 151 l l l.
 152 Interface       Attribute       Value
 153 T{
 154 .BR mcheck (),
 155 .BR mcheck_pedantic (),
 156 .br
 157 .BR mcheck_check_all (),
 158 .BR mprobe ()
 159 T}      Thread safety   T{
 160 MT-Unsafe race:mcheck
 161 .br
 162 const:malloc_hooks
 163 T}
 164 .TE
 165 .sp 1
 166 .SH CONFORMING TO
 167 These functions are GNU extensions.
 168 .SH NOTES
 169 Linking a program with
 170 .I \-lmcheck
 171 and using the
 172 .B MALLOC_CHECK_
 173 environment variable (described in
 174 .BR mallopt (3))
 175 cause the same kinds of errors to be detected.
 176 But, using
 177 .B MALLOC_CHECK_
 178 does not require the application to be relinked.
 179 .\" But is MALLOC_CHECK_ slower?
 180 .SH EXAMPLE
 181 The program below calls
 182 .BR mcheck ()
 183 with a NULL argument and then frees the same block of memory twice.
 184 The following shell session demonstrates what happens
 185 when running the program:
 186 .PP
 187 .in +4n
 188 .EX
 189 .RB "$" " ./a.out"
 190 About to free
 191
 192 About to free a second time
 193 block freed twice
 194 Aborted (core dumped)
 195 .EE
 196 .in
 197 .SS Program source
 198 \&
 199 .EX
 200 #include <stdlib.h>
 201 #include <stdio.h>
 202 #include <mcheck.h>
 203
 204 int
 205 main(int argc, char *argv[])
 206 {
 207     char *p;
 208
 209     if (mcheck(NULL) != 0) {
 210         fprintf(stderr, "mcheck() failed\en");
 211
 212         exit(EXIT_FAILURE);
 213     }
 214
 215     p = malloc(1000);
 216
 217     fprintf(stderr, "About to free\en");
 218     free(p);
 219     fprintf(stderr, "\enAbout to free a second time\en");
 220     free(p);
 221
 222     exit(EXIT_SUCCESS);
 223 }
 224 .EE
 225 .SH SEE ALSO
 226 .BR malloc (3),
 227 .BR mallopt (3),
 228 .BR mtrace (3)