Entry Table

The entry table contains object and offset information that is used to resolve fixup references to the entry points within this module. Not all entry points in the entry table will be exported, some entry points will only be used within the module. An ordinal number is used to index into the entry table. The entry table entries are numbered starting from one. The list of entries are compressed into 'bundles', where possible. The entries within each bundle are all the same size. A bundle starts with a count field which indicates the number of entries in the bundle. The count is followed by a type field which identifies the bundle format. This provides both a means for saving space as well as a mechanism for extending the bundle types. The type field allows the definition of 256 bundle types. The following bundle types will initially be defined:

Unused Entry.
16-bit Entry.
286 Call Gate Entry.
32-bit Entry.
Forwarder Entry.
The bundled entry table has the following format

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      00h ³ CNT ³TYPE ³ BUNDLE INFO . . ³
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Entry Table

CNT = DB Number of entries. This is the number of entries in this bundle. A zero value for the number of entries identifies the end of the entry table. There is no further bundle information when the number of entries is zero. In other words the entry table is terminated by a single zero byte.

TYPE = DB Bundle type. This defines the bundle type which determines the contents of the BUNDLE INFO. The follow types are defined

00h = Unused Entry.
01h = 16-bit Entry.
02h = 286 Call Gate Entry.
03h = 32-bit Entry.
04h = Forwarder Entry.
80h = Parameter Typing Information Present. This bit signifies that additional information is contained in the linear EXE module and will be used in the future for parameter type checking.

The following is the format for each bundle type

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      00h ³ CNT ³TYPE ³
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CNT = DB Number of entries. This is the number of unused entries to skip.

TYPE = DB 0 (Unused Entry)

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00h ³ CNT ³TYPE ³ OBJECT ³ ÃÄÄÄÄÄÅÄÄÄÄÄÁÄÄÄÄÄÂÄÄÄÄÄÙ 04h ³FLAGS³ OFFSET ³ ÃÄÄÄÄÄÅÄÄÄÄÄÂÄÄÄÄÄ´ 07h ³ ... ³ . ³ . ³

CNT = DB Number of entries. This is the number of 16-bit entries in this bundle. The flags and offset value are repeated this number of times.

TYPE = DB 1 (16-bit Entry)

OBJECT = DW Object number. This is the object number for the entries in this bundle.

FLAGS = DB Entry flags. These are the flags for this entry point. They have the following definition.

01h = Exported entry flag.
F8h = Parameter word count mask.

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CNT = DB Number of entries. This is the number of 286 call gate entries in this bundle. The flags, callgate, and offset value are repeated this number of times.

TYPE = DB 2 (286 Call Gate Entry) The 286 Call Gate Entry Point type is needed by the loader only if ring 2 segments are to be supported. 286 Call Gate entries contain 2 extra bytes which are used by the loader to store an LDT callgate selector value.

OBJECT = DW Object number. This is the object number for the entries in this bundle.

FLAGS = DB Entry flags. These are the flags for this entry point. They have the following definition.

01h = Exported entry flag.
F8h = Parameter word count mask.

CALLGATE = DW Callgate selector. The callgate selector is a reserved field used by the loader to store a call gate selector value for references to ring 2 entry points. When a ring 3 reference to a ring 2 entry point is made, the callgate selector with a zero offset is place in the relocation fixup address. The segment number and offset in segment is placed in the LDT callgate.

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CNT = DB Number of entries. This is the number of 32-bit entries in this bundle. The flags and offset value are repeated this number of times.

TYPE = DB 3 (32-bit Entry) The 32-bit Entry type will only be defined by the linker when the offset in the object can not be specified by a 16-bit offset.

OBJECT = DW Object number. This is the object number for the entries in this bundle.

FLAGS = DB Entry flags. These are the flags for this entry point. They have the following definition.

01h = Exported entry flag.
F8h = Parameter dword count mask.

          ÚÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄ¿      00h ³ CNT ³TYPE ³ RESERVED  ³
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      04h ³FLAGS³ MOD ORD#  ³ OFFSET / ORDNUM       ³
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      09h ³ ... ³    ...    ³          ...          ³

CNT = DB Number of entries. This is the number of forwarder entries in this bundle. The FLAGS, MOD ORD#, and OFFSET/ORDNUM values are repeated this number of times.

TYPE = DB 4 (Forwarder Entry)

RESERVED = DW 0 This field is reserved for future use.

FLAGS = DB Forwarder flags. These are the flags for this entry point. They have the following definition.

01h = Import by ordinal.
F7h = Reserved for future use; should be zero.

OFFSET / ORDNUM = DD Procedure Name Offset or Import Ordinal Number If the FLAGS field indicates import by ordinal, then this field is the ordinal number into the Entry Table of the target module, otherwise this field is the offset into the Procedure Names Table of the target module.

A Forwarder entry (type = 4) is an entry point whose value is an imported reference. When a load time fixup occurs whose target is a forwarder, the loader obtains the address imported by the forwarder and uses that imported address to resolve the fixup.

A forwarder may refer to an entry point in another module which is itself a forwarder, so there can be a chain of forwarders. The loader will traverse the chain until it finds a non-forwarded entry point which terminates the chain , and use this to resolve the original fixup. Circular chains are detected by the loader and result in a load time error. A maximum of 1024 forwarders is allowed in a chain; more than this results in a load time error.

Forwarders are useful for merging and recombining API calls into different sets of libraries, while maintaining compatibility with applications. For example, if one wanted to combine MONCALLS, MOUCALLS, and VIOCALLS into a single libraries, one could provide entry points for the three libraries that are forwarders pointing to the common implementation.

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