ii.24.2.6-metadata-stream.md

II.24.2.6 #~ stream

The "#~" streams contain the actual physical representations of the logical metadata tables (§II.22). A "#~" stream has the following top-level structure:

Offset	Size	Field	Description
0	4	Reserved	Reserved, always 0 (§II.24.1).
4	1	MajorVersion	Major version of table schemata; shall be 2 (§II.24.1).
5	1	MinorVersion	Minor version of table schemata; shall be 0 (§II.24.1).
6	1	HeapSizes	Bit vector for heap sizes.
7	1	Reserved	Reserved, always 1 (§II.24.1).
8	8	Valid	Bit vector of present tables, let n be the number of bits that are 1.
16	8	Sorted	Bit vector of sorted tables.
24	4*n	Rows	Array of n 4-byte unsigned integers indicating the number of rows for each present table.
24+4*n		Tables	The sequence of physical tables.

The HeapSizes field is a bitvector that encodes the width of indexes into the various heaps. If bit 0 is set, indexes into the "#Strings" heap are 4 bytes wide; if bit 1 is set, indexes into the "#GUID" heap are 4 bytes wide; if bit 2 is set, indexes into the "#Blob" heap are 4 bytes wide. Conversely, if the HeapSizes bit for a particular heap is not set, indexes into that heap are 2 bytes wide.

Heap size flag	Description
0x01	Size of "#Strings" stream ≥ 216.
0x02	Size of "#GUID" stream ≥ 216.
0x04	Size of "#Blob" stream ≥ 216.

The Valid field is a 64-bit bitvector that has a specific bit set for each table that is stored in the stream; the mapping of tables to indexes is given at the start of §II.22. For example when the DeclSecurity table is present in the logical metadata, bit 0x0e should be set in the Valid vector. It is invalid to include non-existent tables in Valid, so all bits above 0x2c shall be zero.

The Rows array contains the number of rows for each of the tables that are present. When decoding physical metadata to logical metadata, the number of 1's in Valid indicates the number of elements in the Rows array.

A crucial aspect in the encoding of a logical table is its schema. The schema for each table is given in §II.22. For example, the table with assigned index 0x02 is a TypeDef table, which, according to its specification in §II.22.37, has the following columns: a 4-byte-wide flags, an index into the String heap, another index into the String heap, an index into TypeDef, TypeRef, or TypeSpec table, an index into Field table, and an index into MethodDef table.

The physical representation of a table with n columns and m rows with schema (C₀,…,C_n-1) consists of the concatenation of the physical representation of each of its rows. The physical representation of a row with schema (C₀,…,C_n-1) is the concatenation of the physical representation of each of its elements. The physical representation of a row cell e at a column with type C is defined as follows:

• If e is a constant, it is stored using the number of bytes as specified for its column type C (i.e., a 2-bit mask of type PropertyAttributes)

• If e is an index into the GUID heap, 'blob', or String heap, it is stored using the number of bytes as defined in the HeapSizes field.

• If e is a simple index into a table with index i, it is stored using 2 bytes if table i has less than 216 rows, otherwise it is stored using 4 bytes.

• If e is a coded index that points into table t_i out of n possible tables t₀,…t_n-1, then it is stored as e << (log n) | tag{ t₀,…t_n-1 }[ t_i ] using 2 bytes if the maximum number of rows of tables t₀,…t_n-1, is less than 2^{(16 – (log n))}, and using 4 bytes otherwise. The family of finite maps tag{ t₀,…t_n-1 } is defined below. Note that decoding a physical row requires the inverse of this mapping. [For example, the Parent column of the Constant table indexes a row in the Field, Param, or Property tables. The actual table is encoded into the low 2 bits of the number, using the values: 0 => Field, 1 => Param, 2 => Property. The remaining bits hold the actual row number being indexed. For example, a value of 0x321, indexes row number 0xC8 in the Param table.]

TypeDefOrRef: 2 bits to encode tag	Tag
TypeDef	0
TypeRef	1
TypeSpec	2

HasConstant: 2 bits to encode tag	Tag
Field	0
Param	1
Property	2

HasCustomAttribute: 5 bits to encode tag	Tag
MethodDef	0
Field	1
TypeRef	2
TypeDef	3
Param	4
InterfaceImpl	5
MemberRef	6
Module	7
Permission	8
Property	9
Event	10
StandAloneSig	11
ModuleRef	12
TypeSpec	13
Assembly	14
AssemblyRef	15
File	16
ExportedType	17
ManifestResource	18
GenericParam	19
GenericParamConstraint	20
MethodSpec	21

[Note: HasCustomAttributes only has values for tables that are "externally visible"; that is, that correspond to items in a user source program. For example, an attribute can be attached to a TypeDef table and a Field table, but not a ClassLayout table. As a result, some table types are missing from the enum above. end note]

HasFieldMarshall: 1 bit to encode tag	Tag
Field	0
Param	1

HasDeclSecurity: 2 bits to encode tag	Tag
TypeDef	0
MethodDef	1
Assembly	2

MemberRefParent: 3 bits to encode tag	Tag
TypeDef	0
TypeRef	1
ModuleRef	2
MethodDef	3
TypeSpec	4

HasSemantics: 1 bit to encode tag	Tag
Event	0
Property	1

MethodDefOrRef: 1 bit to encode tag	Tag
MethodDef	0
MemberRef	1

MemberForwarded: 1 bit to encode tag	Tag
Field	0
MethodDef	1

Implementation: 2 bits to encode tag	Tag
File	0
AssemblyRef	1
ExportedType	2

CustomAttributeType: 3 bits to encode tag	Tag
Not used	0
Not used	1
MethodDef	2
MemberRef	3
Not used	4

ResolutionScope: 2 bits to encode tag	Tag
Module	0
ModuleRef	1
AssemblyRef	2
TypeRef	3

TypeOrMethodDef: 1 bit to encode tag	Tag
TypeDef	0
MethodDef	1