These notes don't yet get into the compression algorithm, like I mentioned I would in yesterday's Part 2.
Example 3: Decoding a field signature of a generic type declared in another assembly
This example is a little more more complicated due to the field type being a generic type, but it is a simple example of a generic type (only 1 argument and defined in another assembly).
C# code:
private List<TestClass> list = new List<TestClass>();
Field information from ILDasm:
0x06 = IMAGE_CEE_CS_CALLCONV_FIELD
0x15 = ELEMENT_TYPE_GENERICINST
The definition for decoding a GENERICINST is: GENERICINST (CLASS | VALUETYPE) TypeDefOrRefEncoded GenArgCount Type Type*
0x12 = ELEMENT_TYPE_CLASS
0x11 TypeDefOrRefEncoded token
0x11 is a compressed integer of 17 (0x11) - which is the same compressed or uncompressed.
Determine the table the type is in:
If you AND the uncompressed value with 0x03 you can determine which of the least 2 bits are on or off, in this case it will be 01 = TypeRef
Get the index of the record in the table:
Bit shift 17 to the right 2 bits and you get 4 (0x04) - which is the index in the TypeRef table for the System.Collections.Generic.List'1 record.
0x01 = GenArgCount (compressed int32, but in this case it is the same uncompressed)
Only one argument, so just one type to decode:
0x12 = ELEMENT_TYPE_CLASS
0x08 TypeDefOrRefEncoded token
0x08 is also compressed, but is the same either compressed or not
Determine the table the type is in:
Neither of the last 2 bits or on (00 = TypeDef)
Get the index of the record:
Bit shift to the left by 2 and you get 2 (0x02) - which is the index in the TypeDef table for the SignatureUtility.TestClass record.
NOTE: in ILDasm the TypeDef #1 does not match the rid (row or record id) of 2 in the (02 000002) the first (02) is the table index, the 000002 is the rid or index.
Overview
This example walked through the following field declaration:
private List<TestClass> list = new List<TestClass>();
From decoding the signature of this field, you find out the following:
- it is a field
- it is generic
- it is a class
- the type is of System.Collections.Generic.List'1
- it has only 1 generic argument
- the argument type is of SignatureUtility.TestClass