mirror of
https://git.rtems.org/rtems-docs/
synced 2025-05-31 09:21:24 +08:00
199 lines
6.9 KiB
ReStructuredText
199 lines
6.9 KiB
ReStructuredText
Stack Bounds Checker
|
|
####################
|
|
|
|
Introduction
|
|
============
|
|
|
|
The stack bounds checker is an RTEMS support component that determines
|
|
if a task has overrun its run-time stack. The routines provided
|
|
by the stack bounds checker manager are:
|
|
|
|
- ``rtems_stack_checker_is_blown`` - Has the Current Task Blown its Stack
|
|
|
|
- ``rtems_stack_checker_report_usage`` - Report Task Stack Usage
|
|
|
|
Background
|
|
==========
|
|
|
|
Task Stack
|
|
----------
|
|
|
|
Each task in a system has a fixed size stack associated with it. This
|
|
stack is allocated when the task is created. As the task executes, the
|
|
stack is used to contain parameters, return addresses, saved registers,
|
|
and local variables. The amount of stack space required by a task
|
|
is dependent on the exact set of routines used. The peak stack usage
|
|
reflects the worst case of subroutine pushing information on the stack.
|
|
For example, if a subroutine allocates a local buffer of 1024 bytes, then
|
|
this data must be accounted for in the stack of every task that invokes that
|
|
routine.
|
|
|
|
Recursive routines make calculating peak stack usage difficult, if not
|
|
impossible. Each call to the recursive routine consumes *n* bytes
|
|
of stack space. If the routine recursives 1000 times, then ``1000 * *n*`` bytes of stack space are required.
|
|
|
|
Execution
|
|
---------
|
|
|
|
The stack bounds checker operates as a set of task extensions. At
|
|
task creation time, the task's stack is filled with a pattern to
|
|
indicate the stack is unused. As the task executes, it will overwrite
|
|
this pattern in memory. At each task switch, the stack bounds checker's
|
|
task switch extension is executed. This extension checks that:
|
|
|
|
- the last ``n`` bytes of the task's stack have
|
|
not been overwritten. If this pattern has been damaged, it
|
|
indicates that at some point since this task was context
|
|
switch to the CPU, it has used too much stack space.
|
|
|
|
- the current stack pointer of the task is not within
|
|
the address range allocated for use as the task's stack.
|
|
|
|
If either of these conditions is detected, then a blown stack
|
|
error is reported using the ``printk`` routine.
|
|
|
|
The number of bytes checked for an overwrite is processor family dependent.
|
|
The minimum stack frame per subroutine call varies widely between processor
|
|
families. On CISC families like the Motorola MC68xxx and Intel ix86, all
|
|
that is needed is a return address. On more complex RISC processors,
|
|
the minimum stack frame per subroutine call may include space to save
|
|
a significant number of registers.
|
|
|
|
Another processor dependent feature that must be taken into account by
|
|
the stack bounds checker is the direction that the stack grows. On some
|
|
processor families, the stack grows up or to higher addresses as the
|
|
task executes. On other families, it grows down to lower addresses. The
|
|
stack bounds checker implementation uses the stack description definitions
|
|
provided by every RTEMS port to get for this information.
|
|
|
|
Operations
|
|
==========
|
|
|
|
Initializing the Stack Bounds Checker
|
|
-------------------------------------
|
|
|
|
The stack checker is initialized automatically when its task
|
|
create extension runs for the first time.
|
|
|
|
The application must include the stack bounds checker extension set
|
|
in its set of Initial Extensions. This set of extensions is
|
|
defined as ``STACK_CHECKER_EXTENSION``. If using ``<rtems/confdefs.h>``
|
|
for Configuration Table generation, then all that is necessary is
|
|
to define the macro ``CONFIGURE_STACK_CHECKER_ENABLED`` before including``<rtems/confdefs.h>`` as shown below:
|
|
.. code:: c
|
|
|
|
#define CONFIGURE_STACK_CHECKER_ENABLED
|
|
...
|
|
#include <rtems/confdefs.h>
|
|
|
|
Checking for Blown Task Stack
|
|
-----------------------------
|
|
|
|
The application may check whether the stack pointer of currently
|
|
executing task is within proper bounds at any time by calling
|
|
the ``rtems_stack_checker_is_blown`` method. This
|
|
method return ``FALSE`` if the task is operating within its
|
|
stack bounds and has not damaged its pattern area.
|
|
|
|
Reporting Task Stack Usage
|
|
--------------------------
|
|
|
|
The application may dynamically report the stack usage for every task
|
|
in the system by calling the``rtems_stack_checker_report_usage`` routine.
|
|
This routine prints a table with the peak usage and stack size of
|
|
every task in the system. The following is an example of the
|
|
report generated:
|
|
.. code:: c
|
|
|
|
ID NAME LOW HIGH AVAILABLE USED
|
|
0x04010001 IDLE 0x003e8a60 0x003e9667 2952 200
|
|
0x08010002 TA1 0x003e5750 0x003e7b57 9096 1168
|
|
0x08010003 TA2 0x003e31c8 0x003e55cf 9096 1168
|
|
0x08010004 TA3 0x003e0c40 0x003e3047 9096 1104
|
|
0xffffffff INTR 0x003ecfc0 0x003effbf 12160 128
|
|
|
|
Notice the last time. The task id is 0xffffffff and its name is "INTR".
|
|
This is not actually a task, it is the interrupt stack.
|
|
|
|
When a Task Overflows the Stack
|
|
-------------------------------
|
|
|
|
When the stack bounds checker determines that a stack overflow has occurred,
|
|
it will attempt to print a message using ``printk`` identifying the
|
|
task and then shut the system down. If the stack overflow has caused
|
|
corruption, then it is possible that the message cannot be printed.
|
|
|
|
The following is an example of the output generated:
|
|
.. code:: c
|
|
|
|
BLOWN STACK!!! Offending task(0x3eb360): id=0x08010002; name=0x54413120
|
|
stack covers range 0x003e5750 - 0x003e7b57 (9224 bytes)
|
|
Damaged pattern begins at 0x003e5758 and is 128 bytes long
|
|
|
|
The above includes the task id and a pointer to the task control block as
|
|
well as enough information so one can look at the task's stack and
|
|
see what was happening.
|
|
|
|
Routines
|
|
========
|
|
|
|
This section details the stack bounds checker's routines.
|
|
A subsection is dedicated to each of routines
|
|
and describes the calling sequence, related constants, usage,
|
|
and status codes.
|
|
|
|
.. COMMENT: rtems_stack_checker_is_blown
|
|
|
|
STACK_CHECKER_IS_BLOWN - Has Current Task Blown Its Stack
|
|
---------------------------------------------------------
|
|
|
|
**CALLING SEQUENCE:**
|
|
|
|
.. code:: c
|
|
|
|
bool rtems_stack_checker_is_blown( void );
|
|
|
|
**STATUS CODES:**
|
|
|
|
``TRUE`` - Stack is operating within its stack limits
|
|
``FALSE`` - Current stack pointer is outside allocated area
|
|
|
|
**DESCRIPTION:**
|
|
|
|
This method is used to determine if the current stack pointer
|
|
of the currently executing task is within bounds.
|
|
|
|
**NOTES:**
|
|
|
|
This method checks the current stack pointer against
|
|
the high and low addresses of the stack memory allocated when
|
|
the task was created and it looks for damage to the high water
|
|
mark pattern for the worst case usage of the task being called.
|
|
|
|
STACK_CHECKER_REPORT_USAGE - Report Task Stack Usage
|
|
----------------------------------------------------
|
|
|
|
**CALLING SEQUENCE:**
|
|
|
|
.. code:: c
|
|
|
|
void rtems_stack_checker_report_usage( void );
|
|
|
|
**STATUS CODES: NONE**
|
|
|
|
**DESCRIPTION:**
|
|
|
|
This routine prints a table with the peak stack usage and stack space
|
|
allocation of every task in the system.
|
|
|
|
**NOTES:**
|
|
|
|
NONE
|
|
|
|
.. COMMENT: COPYRIGHT (c) 1988-2007.
|
|
|
|
.. COMMENT: On-Line Applications Research Corporation (OAR).
|
|
|
|
.. COMMENT: All rights reserved.
|
|
|