man/man3/TCL_MEM_DEBUG.3 - toolchains/skids - Git at Google

 '\"
 '\" Copyright (c) 1992-1999 Karl Lehenbauer and Mark Diekhans.
 '\" Copyright (c) 2000 by Scriptics Corporation.
 '\" All rights reserved.
 '\"
 '\" RCS: @(#) $Id: TCL_MEM_DEBUG.3,v 1.5 2002/02/26 02:22:20 hobbs Exp $
 '\"
 '\" The definitions below are for supplemental macros used in Tcl/Tk
 '\" manual entries.
 '\"
 '\" .AP type name in/out ?indent?
 '\"	Start paragraph describing an argument to a library procedure.
 '\"	type is type of argument (int, etc.), in/out is either "in", "out",
 '\"	or "in/out" to describe whether procedure reads or modifies arg,
 '\"	and indent is equivalent to second arg of .IP (shouldn't ever be
 '\"	needed;  use .AS below instead)
 '\"
 '\" .AS ?type? ?name?
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 '\"	name are examples of largest possible arguments that will be passed
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 '\"
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 '\"	options follow on successive lines, in four columns separated
 '\"	by tabs.
 '\"
 '\" .SE
 '\"	End of list of standard options for a Tk widget.
 '\"
 '\" .OP cmdName dbName dbClass
 '\"	Start of description of a specific option.  cmdName gives the
 '\"	option's name as specified in the class command, dbName gives
 '\"	the option's name in the option database, and dbClass gives
 '\"	the option's class in the option database.
 '\"
 '\" .UL arg1 arg2
 '\"	Print arg1 underlined, then print arg2 normally.
 '\"
 '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
 '\"
 '\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
 .if t .wh -1.3i ^B
 .nr ^l \n(.l
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 .ie !"\\$4"" .TP \\$4
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 .LP
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 ..
 '\"	# SE - end of list of standard options
 .de SE
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 .ft R
 .LP
 See the \\fBoptions\\fR manual entry for details on the standard options.
 ..
 '\"	# OP - start of full description for a single option
 .de OP
 .LP
 .nf
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 Command-Line Name:	\\fB\\$1\\fR
 Database Name:	\\fB\\$2\\fR
 Database Class:	\\fB\\$3\\fR
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 \\$1\l'|0\(ul'\\$2
 ..
 .TH TCL_MEM_DEBUG 3 8.1 Tcl "Tcl Library Procedures"
 .BS
 .SH NAME
 TCL_MEM_DEBUG \- Compile-time flag to enable Tcl memory debugging.

 .SH DESCRIPTION
 When Tcl is compiled with \fBTCL_MEM_DEBUG\fR defined, a powerful set
 of memory debugging aids are included in the compiled binary.  This
 includes C and Tcl functions which can aid with debugging
 memory leaks, memory allocation overruns, and other memory related
 errors.

 .SH "ENABLING MEMORY DEBUGGING"
 .PP
 To enable memory debugging, Tcl should be recompiled from scratch with
 \fBTCL_MEM_DEBUG\fR defined.  This will also compile in a non-stub
 version of \fBTcl_InitMemory\fR to add the \fBmemory\fR command to Tcl.
 .PP
 \fBTCL_MEM_DEBUG\fR must be either left defined for all modules or undefined
 for all modules that are going to be linked together.  If they are not, link
 errors will occur, with either \fBTclDbCkfree\fR and \fBTcl_DbCkalloc\fR or
 \fBTcl_Ckalloc\fR and \fBTcl_Ckfree\fR being undefined.
 .PP
 Once memory debugging support has been compiled into Tcl, the C
 functions \fBTcl_ValidateAllMemory\fR, and \fBTcl_DumpActiveMemory\fR,
 and the Tcl \fBmemory\fR command can be used to validate and examine
 memory usage.

 .SH "GUARD ZONES"
 .PP
 When memory debugging is enabled, whenever a call to \fBckalloc\fR is
 made, slightly more memory than requested is allocated so the memory debugging
 code can keep track of the allocated memory, and eight-byte ``guard
 zones'' are placed in front of and behind the space that will be
 returned to the caller.  (The sizes of the guard zones are defined by the
 C #define \fBLOW_GUARD_SIZE\fR and #define \fBHIGH_GUARD_SIZE\fR
 in the file \fIgeneric/tclCkalloc.c\fR -- it can
 be extended if you suspect large overwrite problems, at some cost in
 performance.)  A known pattern is written into the guard zones and, on
 a call to \fBckfree\fR, the guard zones of the space being freed are
 checked to see if either zone has been modified in any way.  If one
 has been, the guard bytes and their new contents are identified, and a
 ``low guard failed'' or ``high guard failed'' message is issued.  The
 ``guard failed'' message includes the address of the memory packet and
 the file name and line number of the code that called \fBckfree\fR.
 This allows you to detect the common sorts of one-off problems, where
 not enough space was allocated to contain the data written, for
 example.

 .SH "DEBUGGING DIFFICULT MEMORY CORRUPTION PROBLEMS"
 .PP
 Normally, Tcl compiled with memory debugging enabled will make it easy
 to isolate a corruption problem.  Turning on memory validation with
 the memory command can help isolate difficult problems.  If you
 suspect (or know) that corruption is occurring before the Tcl
 interpreter comes up far enough for you to issue commands, you can set
 \fBMEM_VALIDATE\fR define, recompile tclCkalloc.c and rebuild Tcl.
 This will enable memory validation from the first call to
 \fBckalloc\fR, again, at a large performance impact.
 .PP
 If you are desperate and validating memory on every call to
 \fBckalloc\fR and \fBckfree\fR isn't enough, you can explicitly call
 \fBTcl_ValidateAllMemory\fR directly at any point.  It takes a \fIchar
 *\fR and an \fIint\fR which are normally the filename and line number
 of the caller, but they can actually be anything you want.  Remember
 to remove the calls after you find the problem.

 .SH "SEE ALSO"
 ckalloc, memory, Tcl_ValidateAllMemory, Tcl_DumpActiveMemory

 .SH KEYWORDS
 memory, debug
	'\"
	'\" Copyright (c) 1992-1999 Karl Lehenbauer and Mark Diekhans.
	'\" Copyright (c) 2000 by Scriptics Corporation.
	'\" All rights reserved.
	'\"
	'\" RCS: @(#) $Id: TCL_MEM_DEBUG.3,v 1.5 2002/02/26 02:22:20 hobbs Exp $
	'\"
	'\" The definitions below are for supplemental macros used in Tcl/Tk
	'\" manual entries.
	'\"
	'\" .AP type name in/out ?indent?
	'\" Start paragraph describing an argument to a library procedure.
	'\" type is type of argument (int, etc.), in/out is either "in", "out",
	'\" or "in/out" to describe whether procedure reads or modifies arg,
	'\" and indent is equivalent to second arg of .IP (shouldn't ever be
	'\" needed; use .AS below instead)
	'\"
	'\" .AS ?type? ?name?
	'\" Give maximum sizes of arguments for setting tab stops. Type and
	'\" name are examples of largest possible arguments that will be passed
	'\" to .AP later. If args are omitted, default tab stops are used.
	'\"
	'\" .BS
	'\" Start box enclosure. From here until next .BE, everything will be
	'\" enclosed in one large box.
	'\"
	'\" .BE
	'\" End of box enclosure.
	'\"
	'\" .CS
	'\" Begin code excerpt.
	'\"
	'\" .CE
	'\" End code excerpt.
	'\"
	'\" .VS ?version? ?br?
	'\" Begin vertical sidebar, for use in marking newly-changed parts
	'\" of man pages. The first argument is ignored and used for recording
	'\" the version when the .VS was added, so that the sidebars can be
	'\" found and removed when they reach a certain age. If another argument
	'\" is present, then a line break is forced before starting the sidebar.
	'\"
	'\" .VE
	'\" End of vertical sidebar.
	'\"
	'\" .DS
	'\" Begin an indented unfilled display.
	'\"
	'\" .DE
	'\" End of indented unfilled display.
	'\"
	'\" .SO
	'\" Start of list of standard options for a Tk widget. The
	'\" options follow on successive lines, in four columns separated
	'\" by tabs.
	'\"
	'\" .SE
	'\" End of list of standard options for a Tk widget.
	'\"
	'\" .OP cmdName dbName dbClass
	'\" Start of description of a specific option. cmdName gives the
	'\" option's name as specified in the class command, dbName gives
	'\" the option's name in the option database, and dbClass gives
	'\" the option's class in the option database.
	'\"
	'\" .UL arg1 arg2
	'\" Print arg1 underlined, then print arg2 normally.
	'\"
	'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
	'\"
	'\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
	.if t .wh -1.3i ^B
	.nr ^l \n(.l
	.ad b
	'\" # Start an argument description
	.de AP
	.ie !"\\$4"" .TP \\$4
	.el \{\
	. ie !"\\$2"" .TP \\n()Cu
	. el .TP 15
	.\}
	.ta \\n()Au \\n()Bu
	.ie !"\\$3"" \{\
	\&\\$1 \\fI\\$2\\fP (\\$3)
	.\".b
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	.if !"\\$1"" .nr )A \\w'\\$1'u+3n
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	.\"
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	.nr )C \\n()Bu+\\w'(in/out)'u+2n
	..
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	.\}
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	..
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	'\" # box/sidebar if in box/sidebar mode, then invoked standard
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	'ti 0
	'nf
	.mk ^t
	.if \\n(^b \{\
	.\" Draw three-sided box if this is the box's first page,
	.\" draw two sides but no top otherwise.
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	.\}
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	..
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	..
	'\" # SO - start of list of standard options
	.de SO
	.SH "STANDARD OPTIONS"
	.LP
	.nf
	.ta 5.5c 11c
	.ft B
	..
	'\" # SE - end of list of standard options
	.de SE
	.fi
	.ft R
	.LP
	See the \\fBoptions\\fR manual entry for details on the standard options.
	..
	'\" # OP - start of full description for a single option
	.de OP
	.LP
	.nf
	.ta 4c
	Command-Line Name: \\fB\\$1\\fR
	Database Name: \\fB\\$2\\fR
	Database Class: \\fB\\$3\\fR
	.fi
	.IP
	..
	'\" # CS - begin code excerpt
	.de CS
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	.nf
	.ta .25i .5i .75i 1i
	..
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	.fi
	.RE
	..
	.de UL
	\\$1\l'\|0\(ul'\\$2
	..
	.TH TCL_MEM_DEBUG 3 8.1 Tcl "Tcl Library Procedures"
	.BS
	.SH NAME
	TCL_MEM_DEBUG \- Compile-time flag to enable Tcl memory debugging.

	.SH DESCRIPTION
	When Tcl is compiled with \fBTCL_MEM_DEBUG\fR defined, a powerful set
	of memory debugging aids are included in the compiled binary. This
	includes C and Tcl functions which can aid with debugging
	memory leaks, memory allocation overruns, and other memory related
	errors.

	.SH "ENABLING MEMORY DEBUGGING"
	.PP
	To enable memory debugging, Tcl should be recompiled from scratch with
	\fBTCL_MEM_DEBUG\fR defined. This will also compile in a non-stub
	version of \fBTcl_InitMemory\fR to add the \fBmemory\fR command to Tcl.
	.PP
	\fBTCL_MEM_DEBUG\fR must be either left defined for all modules or undefined
	for all modules that are going to be linked together. If they are not, link
	errors will occur, with either \fBTclDbCkfree\fR and \fBTcl_DbCkalloc\fR or
	\fBTcl_Ckalloc\fR and \fBTcl_Ckfree\fR being undefined.
	.PP
	Once memory debugging support has been compiled into Tcl, the C
	functions \fBTcl_ValidateAllMemory\fR, and \fBTcl_DumpActiveMemory\fR,
	and the Tcl \fBmemory\fR command can be used to validate and examine
	memory usage.

	.SH "GUARD ZONES"
	.PP
	When memory debugging is enabled, whenever a call to \fBckalloc\fR is
	made, slightly more memory than requested is allocated so the memory debugging
	code can keep track of the allocated memory, and eight-byte ``guard
	zones'' are placed in front of and behind the space that will be
	returned to the caller. (The sizes of the guard zones are defined by the
	C #define \fBLOW_GUARD_SIZE\fR and #define \fBHIGH_GUARD_SIZE\fR
	in the file \fIgeneric/tclCkalloc.c\fR -- it can
	be extended if you suspect large overwrite problems, at some cost in
	performance.) A known pattern is written into the guard zones and, on
	a call to \fBckfree\fR, the guard zones of the space being freed are
	checked to see if either zone has been modified in any way. If one
	has been, the guard bytes and their new contents are identified, and a
	``low guard failed'' or ``high guard failed'' message is issued. The
	``guard failed'' message includes the address of the memory packet and
	the file name and line number of the code that called \fBckfree\fR.
	This allows you to detect the common sorts of one-off problems, where
	not enough space was allocated to contain the data written, for
	example.

	.SH "DEBUGGING DIFFICULT MEMORY CORRUPTION PROBLEMS"
	.PP
	Normally, Tcl compiled with memory debugging enabled will make it easy
	to isolate a corruption problem. Turning on memory validation with
	the memory command can help isolate difficult problems. If you
	suspect (or know) that corruption is occurring before the Tcl
	interpreter comes up far enough for you to issue commands, you can set
	\fBMEM_VALIDATE\fR define, recompile tclCkalloc.c and rebuild Tcl.
	This will enable memory validation from the first call to
	\fBckalloc\fR, again, at a large performance impact.
	.PP
	If you are desperate and validating memory on every call to
	\fBckalloc\fR and \fBckfree\fR isn't enough, you can explicitly call
	\fBTcl_ValidateAllMemory\fR directly at any point. It takes a \fIchar
	*\fR and an \fIint\fR which are normally the filename and line number
	of the caller, but they can actually be anything you want. Remember
	to remove the calls after you find the problem.

	.SH "SEE ALSO"
	ckalloc, memory, Tcl_ValidateAllMemory, Tcl_DumpActiveMemory

	.SH KEYWORDS
	memory, debug