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1 | .\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com> |
2 | .\" | |
93015253 | 3 | .\" %%%LICENSE_START(VERBATIM) |
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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14 | .\" manual page may be incorrect or out-of-date.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. | |
4b72fb64 | 23 | .\" %%%LICENSE_END |
fd298193 | 24 | .\" |
67d2c687 | 25 | .TH MCHECK 3 2015-05-07 "GNU" "Linux Programmer's Manual" |
fd298193 | 26 | .SH NAME |
90d4c3de | 27 | mcheck, mcheck_check_all, mcheck_pedantic, mprobe \- heap consistency checking |
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28 | .SH SYNOPSIS |
29 | .nf | |
30 | .B #include <mcheck.h> | |
31 | .sp | |
32 | .BI "int mcheck(void (*" abortfunc ")(enum mcheck_status " mstatus )); | |
33 | ||
34 | .BI "int mcheck_pedantic(void (*" abortfunc ")(enum mcheck_status " mstatus )); | |
3960d7a2 | 35 | |
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36 | .B void mcheck_check_all(void); |
37 | ||
38 | .BI "enum mcheck_status mprobe(void *" ptr ); | |
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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 | ||
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 | |
8f7f19ad | 58 | .IR \-lmcheck |
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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 | ||
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 | ||
72 | The | |
73 | .BR mcheck_check_all () | |
74 | function causes an immediate check on all allocated blocks. | |
33a0ccb2 | 75 | This call is effective only if |
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76 | .BR mcheck () |
77 | is called beforehand. | |
78 | ||
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 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 | ||
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 | ||
104 | The following list describes the values returned by | |
105 | .BR mprobe () | |
106 | or passed as the | |
107 | .I mstatus | |
3960d7a2 | 108 | argument when |
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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 | |
6fdbc779 | 141 | .BR mcheck () |
fd298193 | 142 | and |
6fdbc779 | 143 | .BR mprobe () |
fd298193 | 144 | functions are present since at least glibc 2.0 |
834fde73 ZL |
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 | ||
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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? | |
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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 | .in +4n | |
187 | .nf | |
188 | ||
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 | .fi | |
196 | .in | |
197 | .SS Program source | |
198 | \& | |
199 | .nf | |
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\\n"); | |
211 | ||
212 | exit(EXIT_FAILURE); | |
213 | } | |
214 | ||
215 | p = malloc(1000); | |
216 | ||
217 | fprintf(stderr, "About to free\\n"); | |
218 | free(p); | |
219 | fprintf(stderr, "\\nAbout to free a second time\\n"); | |
220 | free(p); | |
221 | ||
222 | exit(EXIT_SUCCESS); | |
223 | } | |
224 | .fi | |
225 | .SH SEE ALSO | |
226 | .BR malloc (3), | |
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227 | .BR mallopt (3), |
228 | .BR mtrace (3) |