Why does SoftICE sometimes show memory contents as ?? or INVALID ?
Occasionally during the tracing of a process, you will encounter a situation where SoftICE displays a long series of INVALID’s in the code window. This most often occurs when a process is first loaded, and you have breakpointed the entrypoint. To understand this, you need to know a little about paging and virtual memory. Physical memory is divided up into 4K regions, called pages. Each page may either be present in physical memory, or paged out to disk at any given time. When an attempt is made to access a page which is currently paged out to disk, a Page Fault exception is generated by the processor. The Windows kernel handles this exception, loads the page from disk into physical memory, and then re-executes the instruction which caused the page fault (and execution continues as normal). Normally, this is totally transparent to applications, and they are completely unaware there was ever a page fault in the first place. Since SoftICE is a kernel mode debugger, it operates below the w
