malloc.3

对内存的分配、释放和使用进行检查

.TH MALLOC 3 "" "" "1.0"
.ds ]T 
.\"/*
.\" * (c) Copyright 1990 Conor P. Cahill (uunet!virtech!cpcahil).  
.\" * You may copy, distribute, and use this software as long as this
.\" * copyright statement is not removed.
.\" */
.\" $Id: malloc.3,v 1.1 90/05/11 15:53:20 cpcahil Exp $
.SH NAME
malloc \t- debugging malloc library
.SH SYNOPSIS
.ft B
.nf
#include <malloc.h>

char	* calloc(nelem,elsize);
void	  free(ptr);
char	* malloc(size);
int	  malloc_chain_check(flag);
void	  malloc_dump(fd);
int	  mallopt(cmd,value)
char	* realloc(ptr,size);

int		  cmd,fd,flag;
unsigned	  elsize,nelem,size;
char		* ptr;
union val	  value;

.fi
.ft R
.SH DESCRIPTION
This malloc library is a replacement for the standard library to be used
during software development/debugging.  See the standard malloc(3) pages
for more information on the use of the following functions:
.nf
.in +.5i
calloc(), free(), malloc(), realloc()
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.fi
.sp
This library differs from the standard malloc library in the
following ways:
.P
1. Each malloc segment contains a magic number so that free can 
verify that the pointer passed points to a valid malloc segment.
.P
2. Each malloc segment is filled with a non-zero pattern so that code that
depends upon malloc segments being null will fail.
.P
3. The size of each segment will be at least 1 byte larger than requested
and the extra bytes will be filled with a non-zero pattern.  When free is
called, it will verify that you did not go beyond the number of bytes 
you asked for.
.P
4. When a segment is freed, it will be filled with a different non-zero pattern
to ensure that the program doesn't depend upon the use of already freed data.
.P
5. Whenever any of the string or memory functions (str*, b*, mem*) are 
called with a pointer that is within the malloc arena,  the operation is
checked to verify that it does not overrun the malloced segment.  A failure
of this check is considered a "warning level error" (described later) and
is handled accordingly.
.P
7. Run time checking can include verification of the malloc chain at each
and every call to one of the malloc functions or manually by calling the
malloc_chain_check function.
.P
6. When a problem is found, the action taken is specified at runtime by
environment variables or at compile time by the use of the mallopt()
function.
.P
There are two arbitrary levels of errors, warning and fatal, that this
library will detect.  They are broken down as follows:
.P
.nf
.in +.25i
Warning messages include:
.sp
.in +.5i
.ti -.25i
Calling free with a bad pointer
.br
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Calling a bstring/string/memory (3) function which will go beyond
the end of a malloc block. Note that the library function is
not modified to refuse the operation.
.sp
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Fatal errors are:
.in +.5i
.ti -.25i
Detectable corruption to the malloc chain.
.in -.5i
.in -.25i
.P
The error handling for each level (warning or fatal) are specified using
environment variables or mallopt().  The coding for the error handling is
as follows:
.sp
.nf
.in +.5i
.ti -.25i
  0 - continue operations
.ti -.25i
  1 - drop core and exit
.ti -.25i
  2 - just exit
.ti -.25i
  3 - drop core, but continue executing.  Core files will
be placed into core.[PID].[counter] i.e: core.00123.001
.ti -.25i
128 - dump malloc chain and continue
.ti -.25i
129 - dump malloc chain, dump core, and exit
.ti -.25i
130 - dump malloc chain, exit
.ti -.25i
131 - dump malloc chain, dump core, continue processing
.in -.5i
.P
In addition error messages can be placed into an error file.
.P
\fBmalloc_opt\fP() is used to set the malloc debugging options. The
following options can be set:
.br
.sp
.in +.5i
MALLOC_WARN - set the error handling for warning level errors.  \fBval\fP is
an integer that can contain any one of the following values:
.sp
.in +.5i
M_HANDLE_IGNORE - ignore error
.br
M_HANDLE_ABORT - drop core and exit
.br
M_HANDLE_EXIT - just exit (no core drop)
.br
M_HANDLE_CORE - drop core, but keep on going
.br
.in -.5i
.sp
In addition, M_HANDLE_DUMP may be or'd in to cause a dump of the current
malloc chain.
.br
.sp
MALLOC_FATAL - set the error handling for fatal level errors.  \fBval\fP is
equivalent to \fBval\fP for MALLOC_WARN.
.br
.sp
MALLOC_ERRFILE - set the destination for malloc error messages.  \fBval\fP is
a pointer to a character string containing the name of the file to be used
for error messages.
.br
.sp
MALLOC_CKCHAIN - set the malloc chain checking flag.  If \fBval\fP is
non-zero, chain checking at every call to malloc is turned on.
.br
.sp
For example, to set up the session to generate a core file for
every malloc warning, to drop core and exit on a malloc fatal, and 
to log all messages to the file "malloc_log" do the following:
.sp
.nf
.in +.5i
#include <malloc.h>
malloc_opt(MALLOC_WARN,131);
malloc_opt(MALLOC_FATAL,1);
malloc_opt(MALLOC_ERRFILE,"malloc_log");
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.fi
.in -.5i
.sp
\fBmalloc_opt\fP() can be used to set/alter the debugging options at any
time.
.P
\fBmalloc_dump\fP() will dump a table of the malloc arena showing all
allocated/freed segments and the first few bytes of data in each segment.
\fBfd\fP is the file descriptor to write the data to.
.P
\fBmalloc_chain_check\fP() will check the status of the malloc arena.
If \fBflag\fP is non-zero, an error found in the chain will cause a 
fatal error.  \fBmalloc_chain_check\fP() returns zero when there are no
problems found in the malloc chain, non-zero otherwise.
.SH "ENVIRONMENT VARIABLES"
Environment variables can be used to control error handling, error logging
and malloc chain checking at run time.  The following environment variables
are used:
.P
MALLOC_WARN - specifies the error handling for warning errors
.br
MALLOC_FATAL - specifies the error handling for fatal errors
.br
MALLOC_ERRFILE - specifies the error log file for error messages.  
.br
MALLOC_CKCHAIN - if 1, turns on malloc chain checking at every call to any
of the malloc functions.
.P
For example, to set up the session to generate a core file for
every malloc warning, to drop core and exit on a malloc fatal, and 
to log all messages to the file "malloc_log" do the following:
.sp
.nf
.in +.5i
MALLOC_WARN=131
MALLOC_FATAL=1
MALLOC_ERRFILE=malloc_log

export MALLOC_WARN MALLOC_FATAL MALLOC_ERRFILE
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.fi
.SH WARNINGS
This malloc library and it's associated string and memory functions are
much less efficient than the standard functions due in part to the extra
error checking.  You do not want to use this library when generating a
production (i.e. releasable) version of your software.  It should only
be used during development and testing.
.SH SEE ALSO
stat(2)
.SH AUTHOR
Conor P. Cahill
Virtual Technologies Incorporated
.sp
uunet!virtech!cpcahil