In a pure CIL image, a single fixup of type IMAGE_REL_BASED_HIGHLOW (0x3) is required for the x86 startup stub which access the IAT to load the runtime engine on down level loaders. When building a mixed CIL/native image or when the image contains embedded RVAs in user data, the relocation section contains relocations for these as well.
The relocations shall be in their own section, named ".reloc", which shall be the final section in the PE file. The relocation section contains a Fixup Table. The fixup table is broken into blocks of fixups. Each block represents the fixups for a 4K page, and each block shall start on a 32-bit boundary.
Each fixup block starts with the following structure:
| Offset | Size | Field | Description |
|---|---|---|---|
| 0 | 4 | PageRVA | The RVA of the block in which the fixup needs to be applied. The low 12 bits shall be zero. |
| 4 | 4 | Block Size | Total number of bytes in the fixup block, including the Page RVA and Block Size fields, as well as the Type/Offset fields that follow, rounded up to the next multiple of 4. |
The Block Size field is then followed by (BlockSize - 8)/2 Type/Offset. Each entry is a word (2 bytes) and has the following structure (if necessary, insert 2 bytes of 0 to pad to a multiple of 4 bytes in length):
| Offset | Size | Field | Description |
|---|---|---|---|
| 0 | 4 bits | Type | Stored in high 4 bits of word. Value indicating which type of fixup is to be applied (described above) |
| 0 | 12 bits | Offset | Stored in remaining 12 bits of word. Offset from starting address specified in the Page RVA field for the block. This offset specifies where the fixup is to be applied. |