Continuing with the decoding of method signatures, these notes cover non generic methods, generic methods and vararg methods.

Constraint Flags

(from CorGenericParamAttr, CorHdr.h lin 710)

Example 29: Decoding a method signature with 1 parameter with a return type of int

C# Code:

private int method1ParamIntRet(int number)
{
    return number;
}

Method information from ILDasm:

0x20 = IMAGE_CEE_CS_CALLCONV_EXPLICITTHIS (HasThis) and IMAGE_CEE_CS_CALLCONV_DEFAULT (Default)

0x01 = Parameter count of 1

0x08 = Return type = ELEMENT_TYPE_I4

0x08 = Parameter type = ELEMENT_TYPE_I4

This tells us the method is an instance method that takes 1 parameter of type int and returns an int.

NOTE: the return type comes after the parameter count (MethodDefSig)

Example 30: Decoding a method signature with 1 parameter with a return type of a class declared in current assembly

C# Code:

private TestClass method1ParamObjectRet(TestClass tc)
{
    return tc;
}

Method information from ILDasm:

0x20 = IMAGE_CEE_CS_CALLCONV_EXPLICITTHIS (HasThis) and IMAGE_CEE_CS_CALLCONV_DEFAULT (Default)

0x01 = parameter count = 1

0x12 = ELEMENT_TYPE_CLASS (return type)

0x08 = TypeDefOrRefEncoded Token

0x08 is a compressed integer of 8 - which is the same compressed or uncompressed

The TypeDefOrRefEncoded token is a TypeDef and a RID of 2, which is the record SignatureUtility.TestClass in the TypeDef table

0x12 = ELEMENT_TYPE_CLASS (parameter type)

0x08 = TypeDefOrRefEncoded Token - which is the same as above for the return type

This tells us it is an instance method that takes 1 parameter of type SignatureUtility.TestClass and has a return type of SignatureUtility.TestClass

Example 31: Decoding a method signature with 1 Generic Parameter and return type of void

C# Code:

private void methodGeneric0ParamVoidRet<T>()
{ }

Method information from ILDasm:

0x30 = IMAGE_CEE_CS_CALLCONV_EXPLICITTHIS (HasThis) and IMAGE_CEE_CS_CALLCONV_GENERIC (Generic)

0x01 = GenParamCount = 1

0x00 = Parameter Count = 0

0x01 = ELEMENT_TYPE_VOID

If you look at the contents of the GenericParam table, you will see there is a record (RID=2) that has an Owner value of 06000004 which is the current method's token (table type=06 and RID of 000004).

This tells us the method is an instance method that takes 1 Generic Parameter, has no method parameters and returns void.  By looking at the GenericParam table, we can see that the generic parameter's name is T (have to look in the string heap at index 0xc8 for the name 'T').

Example 32: Decoding a method signature with 1 Generic Parameter (with a constraint), 1 parameter and a return type of a type declared in the assembly

C# Code:

private TestClass methodGenericConstraint1ParamObjectRet<T>(int number) 
    where T : TestClass, new()
{
    return new TestClass();
}

Method information from ILDasm:

0x30 = IMAGE_CEE_CS_CALLCONV_EXPLICITTHIS (HasThis) and IMAGE_CEE_CS_CALLCONV_GENERIC (Generic)

0x01 = GenParamCount = 1

0x01 = Parameter Count = 1

0x12 = ELEMENT_TYPE_CLASS (return type)

0x08 = TypeDefOrRefEncoded Token

0x08 is a compressed integer of 8 - which is the same compressed or uncompressed

The TypeDefOrRefEncoded token is a TypeDef and a RID of 2, which is the record SignatureUtility.TestClass in the TypeDef table

0x08 = Parameter type = ELEMENT_TYPE_I4

If you look at the contents of the GenericParam table, you will see there is a record (RID=3) that has an Owner value of 06000005 which is the current method's token (table type=06 and RID of 000005).  This generic parameter also has a constraint flags value of 0x0010 (DefaultConstructorConstraint).

If you look at the contents of the GenericParamConstraint table, you will see there is a record (RID=1) that has an Owner value of 2a000003 which is the constraint mentioned above and a Constraint TypeDefOrRef of 02 000002 (the TypeDef table entry for SignatureUtility.TestClass).

This tells us the method is an instance method that takes 1 Generic Parameter (with the name T), has 1 method parameter (of type int), has a return type of SignatureUtility.TestClass, with a Generic Constraint stating that T must be a SignatureUtility.TestClass type and must have a default constructor.

Example 33: Decoding a method signature with variable arguments and a void return type

I don't think I've ever used this but since it is possible to do, here it is ...

C# Code:

public void VariableArguments(__arglist)
{ }

Method information from ILDasm:

0x25 = IMAGE_CEE_CS_CALLCONV_HASTHIS (0x20) and IMAGE_CEE_CS_CALLCONV_VARARG (0x5)

0x00 = ParamCount

0x01 = ReturnType of 0x1 (ELEMENT_TYPE_VOID)

This tells us the method is an instance method that has varargs (variable arguments) method and has a return type of void.

Example 34:  Decoding a method signature with a params string array parameter and a void return type

This is the recommended way to create a variable arguments method in .Net - notice how the 'params' keyword compiles to an attribute of type System.ParamArrayAttribute (which is actually attached to the parameter not the method).

C# Code:

public void VariableArguments(params string[] wordList)
{ }

Method information from ILDasm:

0x20 = IMAGE_CEE_CS_CALLCONV_EXPLICITTHIS (HasThis) and IMAGE_CEE_CS_CALLCONV_DEFAULT (Default)

0x01 = ParamCount = 1

0x01 = ReturnType of 0x1 (ELEMENT_TYPE_VOID)

Parameter Type information:

0x1d = ELEMENT_TYPE_SZARRAY

0x0e = ELEMENT_TYPE_STRING

This tells us the method is an instance method with 1 parameter that is a string array and a return type of void.

Notes to be provided soon:

1. Some examples of call site signatures (for MethodRefSig)
2. PropertySig
3. LocalVarSig
4. More detail on the Param decoding
5. More detail on the CustomMod decoding
6. More detail on ReturnType decoding
7. StandAloneMethodSig

Then I'll probably move on to decoding CustomAttributes