Article: Q315937
Product(s): Microsoft C Compiler
Version(s): 6.0
Operating System(s):
Keyword(s): kbDSupport kbAudDeveloper kbHOWTOmaster
Last Modified: 22-MAY-2002
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The information in this article applies to:
- Microsoft Visual C++ Standard Edition, version 6.0
- Microsoft Visual C++, 32-bit Editions, version 6.0
- Microsoft Visual C++, 32-bit Professional Edition, version 6.0
- Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0
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IN THIS TASK
- SUMMARY
- Requirements
- Creating a Test Program to Demonstrate Stack Overflow
- Trapping the Exception with __try and __except (Partial Solution)
- Trapping the Exception with __try and __except (Full Solution)
- Verifying That It Works
- Troubleshooting
- REFERENCES
SUMMARY
=======
A thread that exceeds its stack allocation will raise an exception. This
exception can be trapped with the __try and __except keywords in Microsoft
Visual C++. However, without correct handling, subsequent stack overflows will
raise access violation exceptions. This article shows you how to handle stack
overflows more robustly.
Requirements
------------
The following items describe the recommended hardware, software, network
infrastructure, skills, and knowledge and service packs that you need.
- Microsoft Windows NT, Microsoft Windows 2000, or Microsoft Windows XP
Prior knowledge required:
- You must have a good knowledge of Visual C++ programming, including exception
handling.
Creating a Test Program to Demonstrate Stack Overflow
-----------------------------------------------------
1. Start Microsoft Visual C++ 6.0, and then create a new Win32 Console
Application named StackOverflowDemo. In the Win32 Console Application wizard,
select "A simple application", and then click Finish. Click OK to create the
new application.
2. In the Workspace window, click the FileView tab. Expand the StackOverflowDemo
files node, and then expand the Source Files node. Double-click
StackOverflowDemo.cpp to edit this file in the Code window.
3. In StackOverflowDemo.cpp, add the following #include directives after the
existing #include "stdafx.h" directive:
#include <windows.h>
#include <stdio.h>
4. After the #include directives, type the following function. This deliberately
causes a stack overflow:
void StackOverflow(int depth)
{
char blockdata[10000];
printf("Overflow: %d\n", depth);
StackOverflow(depth+1);
}
5. Edit the main function as follows: int main(int argc, char * argv[])
{
StackOverflow(0);
return 0;
}
6. Press F5 to run the program in the debugger. The program displays a series of
messages to the console. These messages have the form "Overflow: n". Each
message indicates a recursive call to the StackOverflow function. Eventually,
a message box appears that displays the following error message:
Unhandled exception in StackOverflowDemo.exe: 0xC00000FD: Stack Overflow.
7. Press OK to dismiss the dialog box. Depending on your configuration, the IDE
may try to find the source for CHKSTK.ASM. If this dialog box appears, press
Cancel. Click the Debug menu, and then click Stop Debugging to close the
program.
Trapping the Exception with __try and __except (Partial Solution)
-----------------------------------------------------------------
In this section, you trap the stack overflow exception using __try and __except.
This solution is incomplete. The first stack overflow will raise a stack
overflow exception. However, subsequent stack overflows cause access violation
exceptions.
1. Modify the main function as follows: int main(int argc, char * argv[])
{
for (;;)
{
__try
{
StackOverflow(0);
}
__except (EXCEPTION_EXECUTE_HANDLER)
{
printf("Exception handler %lX\n", _exception_code());
Sleep(2000);
}
}
return 0;
}
2. Press F5 to run the program in the debugger.
3. The console output proceeds as before, until the stack overflow occurs. The
exception handler message is then printed out. The loop makes sure that the
StackOverflow function is retried.
4. The program displays the following output:
Overflow: 0
Overflow: 1
Overflow: 2
.
.
Exception Handler C00000FD
Overflow: 0
Overflow: 1
Overflow: 2
.
.
Exception Handler C0000005
Overflow: 0
Overflow: 1
Overflow: 2
.
.
Exception Handler C0000005
The first exception is a stack overflow (C00000FD), but subsequent calls to
the StackOverflow function cause an access violation exception (C0000005).
5. Click the Debug menu in Visual C++, and then click Stop Debugging to close
the program.
Trapping the Exception with __try and __except (Full Solution)
--------------------------------------------------------------
If a thread in your application causes an EXCEPTION_STACK_OVERFLOW exception,
then your thread has left its stack in a damaged state. This is in contrast to
other exceptions such as EXCEPTION_ACCESS_VIOLATION or
EXCEPTION_INT_DIVIDE_BY_ZERO, where the stack is not damaged. This is because
the stack is set to an arbitrarily small value when the program is first loaded.
The stack then grows on demand to meet the needs of the thread. This is
implemented by placing a page with PAGE_GUARD access at the end of the current
stack. When your code causes the stack pointer to point to an address on this
page, an exception occurs. The system then does the three following things:
1. Remove the PAGE_GUARD protection on the guard page, so that the thread can
read and write data to the memory.
2. Allocate a new guard page that is located one page below the last one.
3. Rerun the instruction that raised the exception.
In this way, the system can grow the stack for your thread automatically. Each
thread in a process has a maximum stack size. The stack size is set at compile
time by the /STACK:reserve[,commit] linker switch, or by the STACKSIZE statement
in the .def file for the project. When this maximum stack size is exceeded, the
system does the three following things:
- Remove the PAGE_GUARD protection on the guard page, as described earlier.
- Try to allocate a new guard page below the last one. However, this fails
because the maximum stack size has been exceeded.
- Raise an exception, so that the thread can handle it in the exception block.
Notice an important point here: Your stack no longer has a guard page. The next
time that your program grows the stack all the way to the end (where there
should be a guard page), your program writes beyond the end of the stack and
causes an access violation.
You can repair the guard page in the exception handler by using the example shown
in this section.
Modify the main function as follows:
int main(int argc, char* argv[])
{
for (;;)
{
__try
{
StackOverflow(0);
}
__except(EXCEPTION_EXECUTE_HANDLER)
{
LPBYTE lpPage;
static SYSTEM_INFO si;
static MEMORY_BASIC_INFORMATION mi;
static DWORD dwOldProtect;
// Get page size of system
GetSystemInfo(&si);
// Find SP address
_asm mov lpPage, esp;
// Get allocation base of stack
VirtualQuery(lpPage, &mi, sizeof(mi));
// Go to page beyond current page
lpPage = (LPBYTE)(mi.BaseAddress)-si.dwPageSize;
// Free portion of stack just abandoned
if (!VirtualFree(mi.AllocationBase,
(LPBYTE)lpPage - (LPBYTE)mi.AllocationBase,
MEM_DECOMMIT))
{
// If we get here, exit
exit(1);
}
// Reintroduce the guard page
if (!VirtualProtect(lpPage, si.dwPageSize,
PAGE_GUARD | PAGE_READWRITE,
&dwOldProtect))
{
exit(1);
}
printf("Exception handler %lX\n", _exception_code());
Sleep(2000);
}
}
return 0;
}
Verifying That It Works
-----------------------
1. Press F5 to run the program in the debugger.
2. Observe the output from your program. Make sure that all of the exceptions
are stack overflow exceptions (C00000FD). This output shows that you have
successfully replaced the guard page as part of the exception-handling
mechanism.
3. Select the Debug menu in Visual C++, and then click Stop Debugging to close
the program.
Troubleshooting
---------------
This solution uses in-line assembly statements. This means that the solution is
valid only for Intel (x86) versions of Microsoft Windows. It is not suitable for
implementations of Windows on non-Intel architectures (MIPS or Alpha).
REFERENCES
For more detailed information, see Advanced Windows, 3rd Edition, Chapter 7 and
Chapter 16, by Jeffrey Richter, available through Microsoft Press on the
following Web page:
Additional query words:
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Keywords : kbDSupport kbAudDeveloper kbHOWTOmaster
Technology : kbVCsearch kbAudDeveloper kbVC600 kbVC32bitSearch
Version : :6.0
Issue type : kbhowto
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