The fat format is used whenever the tiny format is not sufficient. This can be true for one or more of the following reasons:
-
The method is too large to encode the size (i.e., at least 64 bytes)
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There are exceptions
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There are extra data sections
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There are local variables
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The operand stack needs more than 8 entries
A fat header has the following structure
| Offset | Size | Field | Description |
|---|---|---|---|
| 0 | 12 (bits) | Flags | Flags (CorILMethod_FatFormat shall be set in bits 0:1, see §II.25.4.4) |
| 12 (bits) | 4 (bits) | Size | Size of this header expressed as the count of 4-byte integers occupied (currently 3) |
| 2 | 2 | MaxStack | Maximum number of items on the operand stack |
| 4 | 4 | CodeSize | Size in bytes of the actual method body |
| 8 | 4 | LocalVarSigTok | Meta Data token for a signature describing the layout of the local variables for the method. 0 means there are no local variables present |