Each DLL is found inside of DLLS.bin. The file itself does not contain a header or a way to locate a DLL inside. Instead, the individual DLLs can be located by using the information in DLLS.tab which contains offsets for this file.
An individual DLL contains the following:
.text section.rodata section (optional).data section (optional)A DLL file starts with a header. The header lists offsets to each section, the number of exports, and offsets to the DLL's constructor and destructor functions.
| Offset | Name | Type | Description |
|---|---|---|---|
| 0x0 | textOffset | u32 | Byte offet to .text section. |
| 0x4 | dataOffset | u32 | Byte offet to .data section (or 0xFFFFFFFF if it doesn't exist). |
| 0x8 | rodataOffset | u32 | Byte offet to .rodata section (or 0xFFFFFFFF if it doesn't exist). |
| 0xC | exportCount | u16 | Number of functions this DLL exports. |
| 0x10 | ctorOffset | u32 | Byte offset from .text to the constructor function. |
| 0x14 | dtorOffset | u32 | Byte offset from .text to the destructor function. |
Following the header is the DLL's export table. This defines the "public interface" of the DLL, allowing outside code to invoke functions inside of the DLL through the export table.
Before and after the actual export entries are a 32-bit number with a currently unknown purpose, always with the value of zero. In between is a list of export table entries, with a length of exportCount from the header.
| Offset | Name | Type | Description |
|---|---|---|---|
| 0x18 | unknown1 | u32 | 0x0 |
| 0x1C | exportOffset[0] | u32 | Byte offset from .text to the exported function. |
| ... | ... | ... | ... |
| - | unknown2 | u32 | 0x0 |
The DLL's .text section contains all of the DLL's executable code. This is position-independent code (PIC) making use of the $gp register. After a DLL is relocated, each function (that needs it) starts by setting the $gp register to the current address of the DLL's global offset table . This allows the function to reference other functions and data outside of the function in a position-independent way.
The .rodata section is special as it contains not only the DLL's readonly data but also its global offset table and relocation table.
| .rodata Visualization |
|---|
| Global offset table |
| 0xFFFF_FFFE |
| $gp relocations |
| 0xFFFF_FFFD |
| .data relocations |
| 0xFFFF_FFFF |
| Readonly data... |
The start of .rodata is always the global offset table. Before relocation, this is a list of byte offsets from .text for local symbols and DLLSIMPORT.tab indexes for external symbols. After relocation, this is a list of absolute VRAM addresses to each symbol. The GOT is terminated by 0xFFFF_FFFE.
The first four GOT entries are always for .text, .rodata, .data, and .bss in that order. If a section is not present, its GOT entry will simply point to the start of the next section as if it had a size of zero.
| Offset | Name | Type | Description |
|---|---|---|---|
| 0x0 | textOffset | u32 | Byte offset from .text to .text... always zero. |
| 0x4 | rodataOffset | u32 | Byte offset from .text to .rodata. |
| 0x8 | dataOffset | u32 | Byte offset from .text to .data. |
| 0xC | bssOffset | u32 | Byte offset from .text to .bss. |
| 0x10 | gotEntry[4] | u32 | If the 32nd bit is set (0x80000000), a DLLSIMPORT.tab index, otherwise a byte offset from .text to the symbol. |
| ... | ... | ... | ... |
| - | - | - | 0xFFFF_FFFE |
Immediately following the global offset table is the DLL's relocation table. This is split into two parts: $gp prologue relocations and .data relocations.
First is a list of byte offsets from .text to the $gp prologue of each DLL function that accesses the GOT. At relocation time, these prologues will be updated so that they initialize $gp to the current absolute address of the DLL's GOT. This list is terminated by 0xFFFF_FFFD.
| Offset | Name | Type | Description |
|---|---|---|---|
| 0x0 | gpPrologueOffset[0] | u32 | Byte offset from .text to a function's $gp prologue. |
| ... | ... | ... | ... |
| - | - | - | 0xFFFF_FFFD |
Immediately following the $gp prologue relocations are the .data relocations. These relocations point to values in the .data section that need to be offset by the relocated address of the DLL's .data section. An example would be a global variable initialized to the address of another global variable.
| Offset | Name | Type | Description |
|---|---|---|---|
| 0x0 | dataOffset[0] | u32 | Byte offset from .data to a data value that needs to be relocated. |
| ... | ... | ... | ... |
| - | - | - | 0xFFFF_FFFF |
Dinosaur Planet DLLs do not use standard MIPS $gp prologues:
; Dinosaur Planet's version
; Note that it uses the ori instruction instead of addiu
lui $gp, 0x0
ori $gp, $gp, 0x0
nop