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+INF: Executable-File Header Format                            [P_WinSDK]
+
+3.00
+WINDOWS
+PSSONLY | Windows 3 Developers Notes softlib ENDUSER
+
+Summary:
+
+Note: This article is part of a set of seven articles, collectively
+called the "Windows 3.00 Developer's Notes." More information about
+the contents of the other articles, and procedures for ordering a
+hard-copy set, can be found in the knowledge base article titled "INF:
+The Windows 3.00 Developer's Notes" (Q65260).
+
+This article can be found in the Software/Data Library by searching on
+the word EXEFMT or S12688. EXEFMT was archived using the PKware
+file-compression utility.
+
+More Information:
+
+Microsoft defined the segmented executable file format for Windows
+applications and dynamic-link libraries (DLLs). This file format is
+also referred to as the New Executable Format. This new format is an
+extension of the existing MS-DOS .EXE format (old-style format). The
+purpose of the segmented executable format is to provide the
+information needed to support the dynamic linking and segmentation
+capabilities of the Windows environment.
+
+An executable file contains Microsoft Windows code and data, or
+Windows code, data, and resources. Specific fields have been added to
+the old-style .EXE format header to indicate the existence of the
+segmented file format. The old-style header may contain a valid
+executable program, called a stub program, that will be executed if
+the program is run on MS-DOS (without Windows). This stub program
+usually prints a message indicating that Microsoft Windows is required
+to run the program. The segmented executable format extensions also
+begin with a header that describes the contents and location of the
+executable image in the file. The loader uses this header information
+when it loads the executable segments in memory.
+
+
+======================================================================
+                     OLD-STYLE HEADER EXTENSIONS
+======================================================================
+
+The old-style header contains information the loader expects for a DOS
+executable file. It describes a stub program (WINSTUB) the loader can
+place in memory when necessary, it points to the new-style header, and
+it contains the stub programs relocation table.
+
+The following illustrates the distinct parts of the old-style
+executable format:
+
+        +-------------------------+
+    00h |  Old-style header info  |
+        +-------------------------+
+    20h |        Reserved         |
+        +-------------------------+
+    3Ch |   Offset to segmented   |
+        |       .EXE header       |
+        +-------------------------+
+    40h |  Relocation table and   |
+        |    DOS stub program     |
+        +-------------------------+
+        |  Segmented .EXE Header  |
+        |           .             |
+        |           .             |
+        |           .             |
+
+The word at offset 18h in the old-style .EXE header contains the
+relative byte offset to the stub program's relocation table. If this
+offset is 40h, then the double word at offset 3Ch is assumed to be the
+relative byte offset from the beginning of the file to the beginning
+of the segmented executable header. A new-format .EXE file is
+identified if the segmented executable header contains a valid
+signature. If the signature is not valid, the file is assumed to be an
+old-style format .EXE file. The remainder of the old-style format
+header will describe a DOS program, the stub. The stub may be any
+valid program but will typically be a program that displays an error
+message.
+
+======================================================================
+                         SEGMENTED EXE FORMAT
+======================================================================
+
+Because Windows executable files are often larger than one segment
+(64K), additional information (that does not appear in the old-style
+header) is required so that the loader can load each segment properly.
+The segmented EXE format was developed to provide the loader with this
+information.
+
+The segmented .EXE file has the following format:
+
+        +-----------------+
+    00h |  Old-style EXE  |
+        |      Header     |
+        +-----------------+
+    20h |    Reserved     |
+        +-----------------+
+    3Ch |    Offset to    | ---+
+        | Segmented Header|    |
+        +-----------------+    |
+    40h | Relocation Table|    |
+        |  & Stub Program |    |
+        +-----------------+    |
+        |                 |    |
+        +-----------------+    |
+    xxh |  Segmented EXE  | <--+
+        |      Header     |
+        +-----------------+
+        |  Segment Table  |
+        +-----------------+
+        | Resource Table  |
+        +-----------------+
+        |  Resident Name  |
+        |      Table      |
+        +-----------------+
+        | Module Reference|
+        |      Table      |
+        +-----------------+
+        | Imported Names  |
+        |      Table      |
+        +-----------------+
+        |   Entry Table   |
+        +-----------------+
+        |  Non-Resident   |
+        |   Name Table    |
+        +-----------------+
+        |   Seg #1 Data   |
+        |   Seg #1 Info   |
+        +-----------------+
+                .
+                .
+                .
+        +-----------------+
+        |   Seg #n Data   |
+        |   Seg #n Info   |
+        +-----------------+
+
+
+The following sections describe each of the components that make up
+the segmented EXE format. Each section contains a description of the
+component and the fields in the structures that make up that
+component.
+
+Note: All unused fields and flag bits are reserved for future use and
+must contain 0 (zero) values.
+
+======================================================================
+                         SEGMENTED EXE HEADER
+======================================================================
+
+The segmented EXE header contains general information about the EXE
+file and contains information on the location and size of the other
+sections. The Windows loader copies this section, along with other
+data, into the module table in the system data. The module table is
+internal data used by the loader to manage the loaded executable
+modules in the system and to support dynamic linking.
+
+The following describes the format of the segmented executable header.
+For each field, the offset is given relative to the beginning of the
+segmented header, the size of the field is defined, and a description
+is given.
+
+    Offset Size Description
+    ------ ---- -----------
+
+    00h     DW  Signature word.
+                "N" is low-order byte.
+                "E" is high-order byte.
+
+    02h     DB  Version number of the linker.
+
+    03h     DB  Revision number of the linker.
+
+    04h     DW  Entry Table file offset, relative to the beginning of
+                the segmented EXE header.
+    06h     DW  Number of bytes in the entry table.
+
+    08h     DD  32-bit CRC of entire contents of file.
+                These words are taken as 00 during the calculation.
+
+    0Ch     DW  Flag word.
+                0000h = NOAUTODATA
+                0001h = SINGLEDATA (Shared automatic data segment)
+                0002h = MULTIPLEDATA (Instanced automatic data
+                        segment)
+                2000h = Errors detected at link time, module will not
+                        load.
+                8000h = Library module.
+                        The SS:SP information is invalid, CS:IP points
+                        to an initialization procedure that is called
+                        with AX equal to the module handle. This
+                        initialization procedure must perform a far
+                        return to the caller, with AX not equal to
+                        zero to indicate success, or AX equal to zero
+                        to indicate failure to initialize. DS is set
+                        to the library's data segment if the
+                        SINGLEDATA flag is set. Otherwise, DS is set
+                        to the caller's data segment.
+
+                        A program or DLL can only contain dynamic
+                        links to executable files that have this
+                        library module flag set. One program cannot
+                        dynamic-link to another program.
+
+    0Eh     DW  Segment number of automatic data segment.
+                This value is set to zero if SINGLEDATA and
+                MULTIPLEDATA flag bits are clear, NOAUTODATA is
+                indicated in the flags word.
+
+                A Segment number is an index into the module's segment
+                table. The first entry in the segment table is segment
+                number 1.
+
+    10h     DW  Initial size, in bytes, of dynamic heap added to the
+                data segment. This value is zero if no initial local
+                heap is allocated.
+
+    12h     DW  Initial size, in bytes, of stack added to the data
+                segment. This value is zero to indicate no initial
+                stack allocation, or when SS is not equal to DS.
+
+    14h     DD  Segment number:offset of CS:IP.
+
+    18h     DD  Segment number:offset of SS:SP.
+                If SS equals the automatic data segment and SP equals
+                zero, the stack pointer is set to the top of the
+                automatic data segment just below the additional heap
+                area.
+
+                    +--------------------------+
+                    | additional dynamic heap  |
+                    +--------------------------+ <- SP
+                    |    additional stack      |
+                    +--------------------------+
+                    | loaded auto data segment |
+                    +--------------------------+ <- DS, SS
+
+    1Ch     DW  Number of entries in the Segment Table.
+
+    1Eh     DW  Number of entries in the Module Reference Table.
+    20h     DW  Number of bytes in the Non-Resident Name Table.
+
+    22h     DW  Segment Table file offset, relative to the beginning
+                of the segmented EXE header.
+
+    24h     DW  Resource Table file offset, relative to the beginning
+                of the segmented EXE header.
+
+    26h     DW  Resident Name Table file offset, relative to the
+                beginning of the segmented EXE header.
+
+    28h     DW  Module Reference Table file offset, relative to the
+                beginning of the segmented EXE header.
+
+    2Ah     DW  Imported Names Table file offset, relative to the
+                beginning of the segmented EXE header.
+
+    2Ch     DD  Non-Resident Name Table offset, relative to the
+                beginning of the file.
+
+    30h     DW  Number of movable entries in the Entry Table.
+
+    32h     DW  Logical sector alignment shift count, log(base 2) of
+                the segment sector size (default 9).
+
+    34h     DW  Number of resource entries.
+
+    36h     DB  Executable type, used by loader.
+                  02h = WINDOWS
+
+    37h-3Fh DB  Reserved, currently 0's.
+
+
+======================================================================
+                            SEGMENT TABLE
+======================================================================
+
+The segment table contains an entry for each segment in the executable
+file. The number of segment table entries are defined in the segmented
+EXE header. The first entry in the segment table is segment number 1.
+The following is the structure of a segment table entry.
+
+   Size Description
+   ---- -----------
+
+   DW   Logical-sector offset (n byte) to the contents of the segment
+        data, relative to the beginning of the file. Zero means no
+        file data.
+
+   DW   Length of the segment in the file, in bytes. Zero means 64K.
+
+   DW   Flag word.
+        0007h = TYPE_MASK  Segment-type field.
+        0000h = CODE       Code-segment type.
+        0001h = DATA       Data-segment type.
+        0010h = MOVEABLE   Segment is not fixed.
+        0040h = PRELOAD    Segment will be preloaded; read-only if
+                           this is a data segment.
+        0100h = RELOCINFO  Set if segment has relocation records.
+        F000h = DISCARD    Discard priority.
+
+   DW   Minimum allocation size of the segment, in bytes. Total size
+        of the segment. Zero means 64K.
+
+
+======================================================================
+                            RESOURCE TABLE
+======================================================================
+
+The resource table follows the segment table and contains entries for
+each resource in the executable file. The resource table consists of
+an alignment shift count, followed by a table of resource records. The
+resource records define the type ID for a set of resources. Each
+resource record contains a table of resource entries of the defined
+type. The resource entry defines the resource ID or name ID for the
+resource. It also defines the location and size of the resource. The
+following describes the contents of each of these structures:
+
+   Size Description
+   ---- -----------
+
+   DW   Alignment shift count for resource data.
+
+   A table of resource type information blocks follows. The following
+   is the format of each type information block:
+
+        DW  Type ID. This is an integer type if the high-order bit is
+            set (8000h); otherwise, it is an offset to the type string,
+            the offset is relative to the beginning of the resource
+            table. A zero type ID marks the end of the resource type
+            information blocks.
+
+        DW  Number of resources for this type.
+
+        DD  Reserved.
+
+        A table of resources for this type follows. The following is
+        the format of each resource (8 bytes each):
+
+            DW  File offset to the contents of the resource data,
+                relative to beginning of file. The offset is in terms
+                of the alignment shift count value specified at
+                beginning of the resource table.
+
+            DW  Length of the resource in the file (in bytes).
+
+            DW  Flag word.
+                0010h = MOVEABLE  Resource is not fixed.
+                0020h = PURE      Resource can be shared.
+                0040h = PRELOAD   Resource is preloaded.
+
+            DW  Resource ID. This is an integer type if the high-order
+                bit is set (8000h), otherwise it is the offset to the
+                resource string, the offset is relative to the
+                beginning of the resource table.
+
+            DD  Reserved.
+
+   Resource type and name strings are stored at the end of the
+   resource table. Note that these strings are NOT null terminated and
+   are case sensitive.
+
+   DB   Length of the type or name string that follows. A zero value
+        indicates the end of the resource type and name string, also
+        the end of the resource table.
+
+   DB   ASCII text of the type or name string.
+
+
+======================================================================
+                         RESIDENT-NAME TABLE
+======================================================================
+
+The resident-name table follows the resource table, and contains this
+module's name string and resident exported procedure name strings. The
+first string in this table is this module's name. These name strings
+are case-sensitive and are not null-terminated. The following
+describes the format of the name strings:
+
+   Size Description
+   ---- -----------
+
+   DB   Length of the name string that follows. A zero value indicates
+        the end of the name table.
+
+   DB   ASCII text of the name string.
+
+   DW   Ordinal number (index into entry table). This value is ignored
+        for the module name.
+
+
+======================================================================
+                        MODULE-REFERENCE TABLE
+======================================================================
+
+The module-reference table follows the resident-name table. Each entry
+contains an offset for the module-name string within the imported-
+names table; each entry is 2 bytes long.
+
+   Size Description
+   ---- -----------
+
+   DW   Offset within Imported Names Table to referenced module name
+        string.
+
+
+======================================================================
+                         IMPORTED-NAME TABLE
+======================================================================
+
+The imported-name table follows the module-reference table. This table
+contains the names of modules and procedures that are imported by the
+executable file. Each entry is composed of a 1-byte field that
+contains the length of the string, followed by any number of
+characters. The strings are not null-terminated and are case
+sensitive.
+
+   Size Description
+   ---- -----------
+
+   DB   Length of the name string that follows.
+
+   DB   ASCII text of the name string.
+
+
+======================================================================
+                             ENTRY TABLE
+======================================================================
+
+The entry table follows the imported-name table. This table contains
+bundles of entry-point definitions. Bundling is done to save space in
+the entry table. The entry table is accessed by an ordinal value.
+Ordinal number one is defined to index the first entry in the entry
+table. To find an entry point, the bundles are scanned searching for a
+specific entry point using an ordinal number. The ordinal number is
+adjusted as each bundle is checked. When the bundle that contains the
+entry point is found, the ordinal number is multiplied by the size of
+the bundle's entries to index the proper entry.
+
+The linker forms bundles in the most dense manner it can, under the
+restriction that it cannot reorder entry points to improve bundling.
+The reason for this restriction is that other .EXE files may refer to
+entry points within this bundle by their ordinal number. The following
+describes the format of the entry table bundles.
+
+   Size Description
+   ---- -----------
+
+   DB   Number of entries in this bundle. All records in one bundle
+        are either moveable or refer to the same fixed segment. A zero
+        value in this field indicates the end of the entry table.
+
+   DB   Segment indicator for this bundle. This defines the type of
+        entry table entry data within the bundle. There are three
+        types of entries that are defined.
+
+        000h = Unused entries. There is no entry data in an unused
+               bundle. The next bundle follows this field. This is
+               used by the linker to skip ordinal numbers.
+
+        001h-0FEh = Segment number for fixed segment entries. A fixed
+               segment entry is 3 bytes long and has the following
+               format.
+
+            DB  Flag word.
+                01h = Set if the entry is exported.
+                02h = Set if the entry uses a global (shared) data
+                      segments.
+                      The first assembly-language instruction in the
+                      entry point prologue must be "MOV AX,data
+                      segment number". This may be set only for
+                      SINGLEDATA library modules.
+
+            DW  Offset within segment to entry point.
+
+        0FFH = Moveable segment entries. The entry data contains the
+               segment number for the entry points. A moveable segment
+               entry is 6 bytes long and has the following format.
+
+            DB  Flag word.
+                01h = Set if the entry is exported.
+                02h = Set if the entry uses a global (shared) data
+                      segments.
+
+            INT 3FH.
+
+            DB  Segment number.
+
+            DW  Offset within segment to entry point.
+
+
+======================================================================
+                        NONRESIDENT-NAME TABLE
+======================================================================
+
+The nonresident-name table follows the entry table, and contains a
+module description and nonresident exported procedure name strings.
+The first string in this table is a module description. These name
+strings are case-sensitive and are not null-terminated. The name
+strings follow the same format as those defined in the resident name
+table.
+
+
+======================================================================
+                           PER SEGMENT DATA
+======================================================================
+
+The location and size of the per-segment data is defined in the
+segment table entry for the segment. If the segment has relocation
+fixups, as defined in the segment table entry flags, they directly
+follow the segment data in the file. The relocation fixup information
+is defined as follows:
+
+
+   Size Description
+   ---- -----------
+
+   DW   Number of relocation records that follow.
+
+   A table of relocation records follows. The following is the format
+   of each relocation record.
+
+        DB  Source type.
+            0Fh = SOURCE_MASK
+            00h = LOBYTE
+            02h = SEGMENT
+            03h = FAR_ADDR (32-bit pointer)
+            05h = OFFSET (16-bit offset)
+
+        DB  Flags byte.
+            03h = TARGET_MASK
+            00h = INTERNALREF
+            01h = IMPORTORDINAL
+            02h = IMPORTNAME
+            03h = OSFIXUP
+            04h = ADDITIVE
+
+        DW  Offset within this segment of the source chain.
+            If the ADDITIVE flag is set, then target value is added to
+            the source contents, instead of replacing the source and
+            following the chain. The source chain is an 0FFFFh
+            terminated linked list within this segment of all
+            references to the target.
+
+        The target value has four types that are defined in the flag
+        byte field. The following are the formats for each target
+        type:
+
+        INTERNALREF
+
+            DB  Segment number for a fixed segment, or 0FFh for a
+                movable segment.
+
+            DB  0
+
+            DW  Offset into segment if fixed segment, or ordinal
+                number index into Entry Table if movable segment.
+
+        IMPORTNAME
+
+            DW  Index into module reference table for the imported
+                module.
+
+            DW  Offset within Imported Names Table to procedure name
+                string.
+
+        IMPORTORDINAL
+
+            DW  Index into module reference table for the imported
+                module.
+            DW  Procedure ordinal number.
+
+        OSFIXUP
+
+            DW  Operating system fixup type.
+                Floating-point fixups.
+                0001h = FIARQQ, FJARQQ
+                0002h = FISRQQ, FJSRQQ
+                0003h = FICRQQ, FJCRQQ
+                0004h = FIERQQ
+                0005h = FIDRQQ
+                0006h = FIWRQQ
+
+            DW  0
+
+======================================================================
+
+Microsoft is a registered trademark and Windows is a trademark of
+Microsoft Corporation.
+
+Additional reference words: 3.0