Microsoft KB Archive/70800

PRWIN9103008: One Cause of FatalExit in Debug Enhanced Mode ID Number: Q70800

3.00 WINDOWS buglist3.00 fixlist3.10

Summary:

PROBLEM ID: WIN9103008

SYMPTOMS Running an application under the Microsoft Windows debugging kernel causes a FatalExit message “free memory overwrite at y:x” to appear on the debugging monitor or terminal.

CAUSE For performance reasons, when an application releases a memory page that was previously on the kernel free page list, Windows does not write the kernel’s memory test pattern back into the freed memory. The kernel interprets this as a problem with the application.

RESOLUTION Microsoft has confirmed this to be a problem in Windows version 3.0. Two ways to avoid this problem are as follows:

- During the debugging phase of application development, turn off
  paging by setting Paging=0 in the [386enh] section of the
  SYSTEM.INI file. Changing this setting negatively impacts system
  performance.

- Modify the [kernel] section of the WIN.INI file to set
  EnableFreeChecking=0.

This problem was corrected in Windows version 3.1.

Additional reference words: 3.00