| .\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com> |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
| .\" Permission is granted to make and distribute verbatim copies of this |
| .\" manual provided the copyright notice and this permission notice are |
| .\" preserved on all copies. |
| .\" |
| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
| .\" have taken the same level of care in the production of this manual, |
| .\" which is licensed free of charge, as they might when working |
| .\" professionally. |
| .\" |
| .\" Formatted or processed versions of this manual, if unaccompanied by |
| .\" the source, must acknowledge the copyright and authors of this work. |
| .\" %%%LICENSE_END |
| .\" |
| .TH MCHECK 3 2015-05-07 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| mcheck, mcheck_check_all, mcheck_pedantic, mprobe \- heap consistency checking |
| .SH SYNOPSIS |
| .nf |
| .B #include <mcheck.h> |
| .sp |
| .BI "int mcheck(void (*" abortfunc ")(enum mcheck_status " mstatus )); |
| |
| .BI "int mcheck_pedantic(void (*" abortfunc ")(enum mcheck_status " mstatus )); |
| |
| .B void mcheck_check_all(void); |
| |
| .BI "enum mcheck_status mprobe(void *" ptr ); |
| .fi |
| .SH DESCRIPTION |
| The |
| .BR mcheck () |
| function installs a set of debugging hooks for the |
| .BR malloc (3) |
| family of memory-allocation functions. |
| These hooks cause certain consistency checks to be performed |
| on the state of the heap. |
| The checks can detect application errors such as freeing a block of memory |
| more than once or corrupting the bookkeeping data structures |
| that immediately precede a block of allocated memory. |
| |
| To be effective, the |
| .BR mcheck () |
| function must be called before the first call to |
| .BR malloc (3) |
| or a related function. |
| In cases where this is difficult to ensure, linking the program with |
| .IR \-lmcheck |
| inserts an implicit call to |
| .BR mcheck () |
| (with a NULL argument) |
| before the first call to a memory-allocation function. |
| |
| The |
| .BR mcheck_pedantic () |
| function is similar to |
| .BR mcheck (), |
| but performs checks on all allocated blocks whenever |
| one of the memory-allocation functions is called. |
| This can be very slow! |
| |
| The |
| .BR mcheck_check_all () |
| function causes an immediate check on all allocated blocks. |
| This call is effective only if |
| .BR mcheck () |
| is called beforehand. |
| |
| If the system detects an inconsistency in the heap, |
| the caller-supplied function pointed to by |
| .I abortfunc |
| is invoked with a single argument, |
| .IR mstatus , |
| that indicates what type of inconsistency was detected. |
| If |
| .I abortfunc |
| is NULL, a default function prints an error message on |
| .IR stderr |
| and calls |
| .BR abort (3). |
| |
| The |
| .BR mprobe () |
| function performs a consistency check on |
| the block of allocated memory pointed to by |
| .IR ptr . |
| The |
| .BR mcheck () |
| function should be called beforehand (otherwise |
| .BR mprobe () |
| returns |
| .BR MCHECK_DISABLED ). |
| |
| The following list describes the values returned by |
| .BR mprobe () |
| or passed as the |
| .I mstatus |
| argument when |
| .I abortfunc |
| is invoked: |
| .TP |
| .BR MCHECK_DISABLED " (" mprobe "() only)" |
| .BR mcheck () |
| was not called before the first memory allocation function was called. |
| Consistency checking is not possible. |
| .TP |
| .BR MCHECK_OK " (" mprobe "() only)" |
| No inconsistency detected. |
| .TP |
| .B MCHECK_HEAD |
| Memory preceding an allocated block was clobbered. |
| .TP |
| .B MCHECK_TAIL |
| Memory following an allocated block was clobbered. |
| .TP |
| .B |
| MCHECK_FREE |
| A block of memory was freed twice. |
| .SH RETURN VALUE |
| .BR mcheck () |
| and |
| .BR mcheck_pedantic () |
| return 0 on success, or \-1 on error. |
| .SH VERSIONS |
| The |
| .BR mcheck_pedantic () |
| and |
| .BR mcheck_check_all () |
| functions are available since glibc 2.2. |
| The |
| .BR mcheck () |
| and |
| .BR mprobe () |
| functions are present since at least glibc 2.0 |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lbw28 lb lbw21 |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR mcheck (), |
| .BR mcheck_pedantic (), |
| .br |
| .BR mcheck_check_all (), |
| .BR mprobe () |
| T} Thread safety T{ |
| MT-Unsafe race:mcheck |
| .br |
| const:malloc_hooks |
| T} |
| .TE |
| |
| .SH CONFORMING TO |
| These functions are GNU extensions. |
| .SH NOTES |
| Linking a program with |
| .I \-lmcheck |
| and using the |
| .B MALLOC_CHECK_ |
| environment variable (described in |
| .BR mallopt (3)) |
| cause the same kinds of errors to be detected. |
| But, using |
| .B MALLOC_CHECK_ |
| does not require the application to be relinked. |
| .\" But is MALLOC_CHECK_ slower? |
| .SH EXAMPLE |
| The program below calls |
| .BR mcheck () |
| with a NULL argument and then frees the same block of memory twice. |
| The following shell session demonstrates what happens |
| when running the program: |
| .in +4n |
| .nf |
| |
| .RB "$" " ./a.out" |
| About to free |
| |
| About to free a second time |
| block freed twice |
| Aborted (core dumped) |
| .fi |
| .in |
| .SS Program source |
| \& |
| .nf |
| #include <stdlib.h> |
| #include <stdio.h> |
| #include <mcheck.h> |
| |
| int |
| main(int argc, char *argv[]) |
| { |
| char *p; |
| |
| if (mcheck(NULL) != 0) { |
| fprintf(stderr, "mcheck() failed\\n"); |
| |
| exit(EXIT_FAILURE); |
| } |
| |
| p = malloc(1000); |
| |
| fprintf(stderr, "About to free\\n"); |
| free(p); |
| fprintf(stderr, "\\nAbout to free a second time\\n"); |
| free(p); |
| |
| exit(EXIT_SUCCESS); |
| } |
| .fi |
| .SH SEE ALSO |
| .BR malloc (3), |
| .BR mallopt (3), |
| .BR mtrace (3) |