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2006-09-13 Joel Sherrill <joel@OARcorp.com>
* new_chapters/Makefile.am, user/Makefile.am, user/c_user.texi, user/dirstat.texi, user/task.t: Move stack to first class citizen status. Include it in User Manual and rename to start with rtems_. * user/stackchk.t: New file. * new_chapters/stackchk.t: Removed.
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Joel Sherrill
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doc/user/stackchk.t
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@c
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@c COPYRIGHT (c) 1988-2006.
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@c On-Line Applications Research Corporation (OAR).
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@c All rights reserved.
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@c
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@c $Id$
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@c
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@chapter Stack Bounds Checker
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@section Introduction
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The stack bounds checker is an RTEMS support component that determines
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if a task has overflowed its run-time stack. The routines provided
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by the stack bounds checker manager are:
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@itemize @bullet
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@item @code{@value{DIRPREFIX}stack_checker_initialize} - Initialize the Stack Bounds Checker
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@item @code{@value{DIRPREFIX}stack_checker_dump_usage} - Report Task Stack Usage
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@end itemize
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@section Background
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@subsection Task Stack
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Each task in a system has a fixed size stack associated with it. This
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stack is allocated when the task is created. As the task executes, the
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stack is used to contain parameters, return addresses, saved registers,
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and local variables. The amount of stack space required by a task
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is dependent on the exact set of routines used. The peak stack usage
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reflects the worst case of subroutine pushing information on the stack.
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For example, if a subroutine allocates a local buffer of 1024 bytes, then
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this data must be accounted for in the stack of every task that invokes that
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routine.
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Recursive routines make calculating peak stack usage difficult, if not
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impossible. Each call to the recursive routine consumes @i{n} bytes
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of stack space. If the routine recursives 1000 times, then @code{1000 * @i{n}}
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bytes of stack space are required.
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@subsection Execution
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The stack bounds checker operates as a set of task extensions. At
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task creation time, the task's stack is filled with a pattern to
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indicate the stack is unused. As the task executes, it will overwrite
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this pattern in memory. At each task switch, the stack bounds checker's
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task switch extension is executed. This extension checks that the last
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@code{n} bytes of the task's stack have not been overwritten. If they
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have, then a blown stack error is reported.
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The number of bytes checked for an overwrite is processor family dependent.
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The minimum stack frame per subroutine call varies widely between processor
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families. On CISC families like the Motorola MC68xxx and Intel ix86, all
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that is needed is a return address. On more complex RISC processors,
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the minimum stack frame per subroutine call may include space to save
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a significant number of registers.
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Another processor dependent feature that must be taken into account by
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the stack bounds checker is the direction that the stack grows. On some
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processor families, the stack grows up or to higher addresses as the
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task executes. On other families, it grows down to lower addresses. The
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stack bounds checker implementation uses the stack description definitions
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provided by every RTEMS port to get for this information.
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@section Operations
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@subsection Initializing the Stack Bounds Checker
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The stack checker is initialized automatically when its task
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create extension runs for the first time. When this occurs,
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the @code{@value{DIRPREFIX}stack_checker_initialize} is invoked.
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The application must include the stack bounds checker extension set
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in its set of Initial Extensions. This set of extensions is
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defined as @code{STACK_CHECKER_EXTENSION}. If using @code{<confdefs.h>}
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for Configuration Table generation, then all that is necessary is
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to define the macro @code{STACK_CHECKER_ON} before including
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@code{<confdefs.h>} as shown below:
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@example
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@group
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#define STACK_CHECKER_ON
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...
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#include <confdefs.h>
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@end group
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@end example
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@subsection Reporting Task Stack Usage
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The application may dynamically report the stack usage for every task
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in the system by calling the @code{@value{DIRPREFIX}stack_checker_dump_usage} routine.
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This routine prints a table with the peak usage and stack size of
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every task in the system. The following is an example of the
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report generated:
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@example
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@group
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ID NAME LOW HIGH AVAILABLE USED
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0x04010001 IDLE 0x003e8a60 0x003e9667 2952 200
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0x08010002 TA1 0x003e5750 0x003e7b57 9096 1168
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0x08010003 TA2 0x003e31c8 0x003e55cf 9096 1168
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0x08010004 TA3 0x003e0c40 0x003e3047 9096 1104
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0xffffffff INTR 0x003ecfc0 0x003effbf 12160 128
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@end group
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@end example
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Notice the last time. The task id is 0xffffffff and its name is "INTR".
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This is not actually a task, it is the interrupt stack.
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@subsection When a Task Overflows the Stack
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When the stack bounds checker determines that a stack overflow has occurred,
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it will attempt to print a message identifying the task and then shut the
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system down. If the stack overflow has caused corruption, then it is
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possible that the message can not be printed.
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The following is an example of the output generated:
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@example
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@group
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BLOWN STACK!!! Offending task(0x3eb360): id=0x08010002; name=0x54413120
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stack covers range 0x003e5750 - 0x003e7b57 (9224 bytes)
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Damaged pattern begins at 0x003e5758 and is 128 bytes long
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@end group
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@end example
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The above includes the task id and a pointer to the task control block as
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well as enough information so one can look at the task's stack and
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see what was happening.
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@section Routines
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This section details the stack bounds checker's routines.
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A subsection is dedicated to each of routines
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and describes the calling sequence, related constants, usage,
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and status codes.
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@page
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@subsection stack_checker_initialize - Initialize the Stack Bounds Checker
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@subheading CALLING SEQUENCE:
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@ifset is-C
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@example
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void rtems_stack_checker_initialize( void );
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@end example
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@end ifset
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@ifset is-Ada
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@example
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An Ada interface is not currently available.
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@end example
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@end ifset
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@subheading STATUS CODES: NONE
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@subheading DESCRIPTION:
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Initialize the stack bounds checker.
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@subheading NOTES:
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This is performed automatically the first time the stack bounds checker
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task create extension executes.
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@page
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@subsection stack_checker_dump_usage - Report Task Stack Usage
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@subheading CALLING SEQUENCE:
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@ifset is-C
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@example
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void rtems_stack_checker_dump_usage( void );
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@end example
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@end ifset
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@ifset is-Ada
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@example
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An Ada interface is not currently available.
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@end example
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@end ifset
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@subheading STATUS CODES: NONE
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@subheading DESCRIPTION:
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This routine prints a table with the peak stack usage and stack space
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allocation of every task in the system.
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@subheading NOTES:
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NONE
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