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diff --git a/man3/mcheck.3 b/man3/mcheck.3 new file mode 100644 index 0000000..97f217f --- /dev/null +++ b/man3/mcheck.3 @@ -0,0 +1,214 @@ +'\" t +.\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH mcheck 3 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +mcheck, mcheck_check_all, mcheck_pedantic, mprobe \- heap consistency checking +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <mcheck.h> +.PP +.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); +.PP +.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. +.PP +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 +.I \-lmcheck +inserts an implicit call to +.BR mcheck () +(with a NULL argument) +before the first call to a memory-allocation function. +.PP +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! +.PP +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. +.PP +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 +.I stderr +and calls +.BR abort (3). +.PP +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 ). +.PP +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 ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR mcheck (), +.BR mcheck_pedantic (), +.BR mcheck_check_all (), +.BR mprobe () +T} Thread safety T{ +.na +.nh +MT-Unsafe race:mcheck +const:malloc_hooks +T} +.TE +.sp 1 +.SH STANDARDS +GNU. +.SH HISTORY +.TP +.BR mcheck_pedantic () +.TQ +.BR mcheck_check_all () +glibc 2.2. +.TP +.BR mcheck () +.TQ +.BR mprobe () +glibc 2.0. +.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 EXAMPLES +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: +.PP +.in +4n +.EX +.RB "$" " ./a.out" +About to free +\& +About to free a second time +block freed twice +Aborted (core dumped) +.EE +.in +.SS Program source +\& +.\" SRC BEGIN (mcheck.c) +.EX +#include <mcheck.h> +#include <stdio.h> +#include <stdlib.h> +\& +int +main(void) +{ + char *p; +\& + if (mcheck(NULL) != 0) { + fprintf(stderr, "mcheck() failed\en"); +\& + exit(EXIT_FAILURE); + } +\& + p = malloc(1000); +\& + fprintf(stderr, "About to free\en"); + free(p); + fprintf(stderr, "\enAbout to free a second time\en"); + free(p); +\& + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SH SEE ALSO +.BR malloc (3), +.BR mallopt (3), +.BR mtrace (3) |