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[PDB Docs] Start documenting CodeView Type Records.
This puts the general layout of the document in place and fully describes 1 simple type record. Followups will fill out more pieces. llvm-svn: 358119
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Zachary Turner
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=====================================
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CodeView Type Records
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=====================================
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=====================================
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CodeView Type Records
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=====================================
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.. contents::
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:local:
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.. _types_intro:
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Introduction
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============
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This document describes the usage and serialization format of the various
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CodeView type records that LLVM understands. This document does not describe
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every single CodeView type record that is defined. In some cases, this is
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because the records are clearly deprecated and can only appear in very old
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software (e.g. the 16-bit types). On other cases, it is because the records
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have never been observed in practice. This could be because they are only
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generated for non-C++ code (e.g. Visual Basic, C#), or because they have been
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made obsolete by newer records, or any number of other reasons. However, the
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records we describe here should cover 99% of type records that one can expect
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to encounter when dealing with modern C++ toolchains.
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Record Categories
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=================
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We can think of a sequence of CodeView type records as an array of variable length
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`leaf records`. Each such record describes its own length as part of a fixed-size
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header, as well as the kind of record it is. Leaf records are either padded to 4
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bytes (if this type stream appears in a TPI/IPI stream of a PDB) or not padded at
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all (if this type stream appears in the ``.debug$T`` section of an object file).
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Padding is implemented by inserting a decreasing sequence of `<_padding_records>`
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that terminates with ``LF_PAD0``.
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The final category of record is a ``member record``. One particular leaf type --
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``LF_FIELDLIST`` -- contains a series of embedded records. While the outer
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``LF_FIELDLIST`` describes its length (like any other leaf record), the embedded
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records -- called ``member records`` do not.
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.. _leaf_types:
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Leaf Records
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------------
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All leaf records begin with the following 4 byte prefix:
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.. code-block:: c++
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struct RecordHeader {
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uint16_t RecordLen; // Record length, not including this 2 byte field.
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uint16_t RecordKind; // Record kind enum.
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};
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LF_POINTER (0x1002)
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^^^^^^^^^^^^^^^^^^^
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**Usage:** Describes a pointer to another type.
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**Layout:**
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.. code-block:: none
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.--------------------.-- +0
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| Referent Type |
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.--------------------.-- +4
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| Attributes |
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.--------------------.-- +8
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| Member Ptr Info | Only present if |Attributes| indicates this is a member pointer.
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.--------------------.-- +E
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Attributes is a bitfield with the following layout:
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.. code-block:: none
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.-----------------------------------------------------------------------------------------------------.
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| Unused | Flags | Size | Modifiers | Mode | Kind |
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.-----------------------------------------------------------------------------------------------------.
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| | | | | | |
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0x100 +0x16 +0x13 +0xD +0x8 +0x5 +0x0
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where the various fields are defined by the following enums:
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.. code-block:: c++
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enum class PointerKind : uint8_t {
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Near16 = 0x00, // 16 bit pointer
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Far16 = 0x01, // 16:16 far pointer
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Huge16 = 0x02, // 16:16 huge pointer
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BasedOnSegment = 0x03, // based on segment
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BasedOnValue = 0x04, // based on value of base
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BasedOnSegmentValue = 0x05, // based on segment value of base
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BasedOnAddress = 0x06, // based on address of base
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BasedOnSegmentAddress = 0x07, // based on segment address of base
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BasedOnType = 0x08, // based on type
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BasedOnSelf = 0x09, // based on self
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Near32 = 0x0a, // 32 bit pointer
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Far32 = 0x0b, // 16:32 pointer
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Near64 = 0x0c // 64 bit pointer
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};
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enum class PointerMode : uint8_t {
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Pointer = 0x00, // "normal" pointer
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LValueReference = 0x01, // "old" reference
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PointerToDataMember = 0x02, // pointer to data member
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PointerToMemberFunction = 0x03, // pointer to member function
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RValueReference = 0x04 // r-value reference
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};
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enum class PointerModifiers : uint8_t {
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None = 0x00, // "normal" pointer
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Flat32 = 0x01, // "flat" pointer
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Volatile = 0x02, // pointer is marked volatile
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Const = 0x04, // pointer is marked const
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Unaligned = 0x08, // pointer is marked unaligned
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Restrict = 0x10, // pointer is marked restrict
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};
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enum class PointerFlags : uint8_t {
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WinRTSmartPointer = 0x01, // pointer is a WinRT smart pointer
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LValueRefThisPointer = 0x02, // pointer is a 'this' pointer of a member function with ref qualifier (e.g. void X::foo() &)
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RValueRefThisPointer = 0x04 // pointer is a 'this' pointer of a member function with ref qualifier (e.g. void X::foo() &&)
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};
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The ``Size`` field of the Attributes bitmask is a 1-byte value indicating the
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pointer size. For example, a `void*` would have a size of either 4 or 8 depending
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on the target architecture. On the other hand, if ``Mode`` indicates that this is
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a pointer to member function or pointer to data member, then the size can be any
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implementation defined number.
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The ``Member Ptr Info`` field of the ``LF_POINTER`` record is only present if the
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attributes indicate that this is a pointer to member.
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Note that "plain" pointers to primitive types are not represented by ``LF_POINTER``
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records, they are indicated by special reserved :ref:`TypeIndex values <type_indices>`.
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LF_MODIFIER (0x1001)
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^^^^^^^^^^^^^^^^^^^^
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LF_PROCEDURE (0x1008)
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^^^^^^^^^^^^^^^^^^^^^
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LF_MFUNCTION (0x1009)
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^^^^^^^^^^^^^^^^^^^^^
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LF_LABEL (0x000e)
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^^^^^^^^^^^^^^^^^
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LF_ARGLIST (0x1201)
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^^^^^^^^^^^^^^^^^^^
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LF_FIELDLIST (0x1203)
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^^^^^^^^^^^^^^^^^^^^^
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LF_ARRAY (0x1503)
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^^^^^^^^^^^^^^^^^
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LF_CLASS (0x1504)
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^^^^^^^^^^^^^^^^^
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LF_STRUCTURE (0x1505)
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^^^^^^^^^^^^^^^^^^^^^
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LF_INTERFACE (0x1519)
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^^^^^^^^^^^^^^^^^^^^^
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LF_UNION (0x1506)
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^^^^^^^^^^^^^^^^^
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LF_ENUM (0x1507)
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^^^^^^^^^^^^^^^^
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LF_TYPESERVER2 (0x1515)
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^^^^^^^^^^^^^^^^^^^^^^^
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LF_VFTABLE (0x151d)
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^^^^^^^^^^^^^^^^^^^
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LF_VTSHAPE (0x000a)
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^^^^^^^^^^^^^^^^^^^
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LF_BITFIELD (0x1205)
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^^^^^^^^^^^^^^^^^^^^
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LF_FUNC_ID (0x1601)
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^^^^^^^^^^^^^^^^^^^
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LF_MFUNC_ID (0x1602)
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^^^^^^^^^^^^^^^^^^^^
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LF_BUILDINFO (0x1603)
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^^^^^^^^^^^^^^^^^^^^^
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LF_SUBSTR_LIST (0x1604)
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^^^^^^^^^^^^^^^^^^^^^^^
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LF_STRING_ID (0x1605)
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^^^^^^^^^^^^^^^^^^^^^
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LF_UDT_SRC_LINE (0x1606)
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^^^^^^^^^^^^^^^^^^^^^^^^
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LF_UDT_MOD_SRC_LINE (0x1607)
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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LF_METHODLIST (0x1206)
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^^^^^^^^^^^^^^^^^^^^^^
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LF_PRECOMP (0x1509)
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^^^^^^^^^^^^^^^^^^^
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LF_ENDPRECOMP (0x0014)
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^^^^^^^^^^^^^^^^^^^^^^
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.. _member_types:
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Member Records
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--------------
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LF_BCLASS (0x1400)
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^^^^^^^^^^^^^^^^^^
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LF_BINTERFACE (0x151a)
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^^^^^^^^^^^^^^^^^^^^^^
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LF_VBCLASS (0x1401)
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^^^^^^^^^^^^^^^^^^^
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LF_IVBCLASS (0x1402)
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^^^^^^^^^^^^^^^^^^^^
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LF_VFUNCTAB (0x1409)
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^^^^^^^^^^^^^^^^^^^^
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LF_STMEMBER (0x150e)
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^^^^^^^^^^^^^^^^^^^^
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LF_METHOD (0x150f)
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^^^^^^^^^^^^^^^^^^
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LF_MEMBER (0x150d)
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^^^^^^^^^^^^^^^^^^
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LF_NESTTYPE (0x1510)
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^^^^^^^^^^^^^^^^^^^^
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LF_ONEMETHOD (0x1511)
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^^^^^^^^^^^^^^^^^^^^^
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LF_ENUMERATE (0x1502)
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^^^^^^^^^^^^^^^^^^^^^
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LF_INDEX (0x1404)
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^^^^^^^^^^^^^^^^^
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.. _padding_records:
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Padding Records
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---------------
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LF_PADn (0xf0 + n)
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^^^^^^^^^^^^^^^^^^
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