Object Page Table

The Object page table provides information about a logical page in an object. A logical page may be an enumerated page, a pseudo page or an iterated page. The structure of the object page table in conjunction with the structure of the object table allows for efficient access of a page when a page fault occurs, while still allowing the physical page data to be located in the preload page, demand load page or iterated data page sections in the linear EXE module. The logical page entries in the Object Page Table are numbered starting from one. The Object Page Table is parallel to the Fixup Page Table as they are both indexed by the logical page number. Each Object Page Table entry has the following format

         63                     32 31       16 15         0
          ﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
      00h ｳ    PAGE DATA OFFSET   ｳ DATA SIZE ｳ   FLAGS   ｳ
          ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ

Object Page Table Entry

PAGE DATA OFFSET = DD Offset to the page data in the EXE file. This field, when bit shifted left by the PAGE OFFSET SHIFT from the module header, specifies the offset from the beginning of the Preload Page section of the physical page data in the EXE file that corresponds to this logical page entry. The page data may reside in the Preload Pages, Demand Load Pages or the Iterated Data Pages sections. If the FLAGS field specifies that this is a Zero-Filled page then the PAGE DATA OFFSET field will contain a 0. If the logical page is specified as an iterated data page, as indicated by the FLAGS field, then this field specifies the offset into the Iterated Data Pages section. The logical page number (Object Page Table index), is used to index the Fixup Page Table to find any fixups associated with the logical page.

DATA SIZE = DW Number of bytes of data for this page. This field specifies the actual number of bytes that represent the page in the file. If the PAGE SIZE field from the module header is greater than the value of this field and the FLAGS field indicates a Legal Physical Page, the remaining bytes are to be filled with zeros. If the FLAGS field indicates an Iterated Data Page, the iterated data records will completely fill out the remainder.

FLAGS = DW Attributes specifying characteristics of this logical page. The bit definitions for this word field follow,

00h = Legal Physical Page in the module (Offset from Preload Page Section).
01h = Iterated Data Page (Offset from Iterated Data Pages Section).
02h = Invalid Page (zero).
03h = Zero Filled Page (zero).
04h = Range of Pages.

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