DOL File Format

Introduction

A DOL is a program for the Nintendo GameCube and the Wii: the main executable of a game (main.dol or boot.dol on a disc or in a channel), a homebrew program, or what a loader such as the Homebrew Channel starts. It is a header of 256 bytes that lists up to seven text (code) sections and eleven data sections, where each goes in memory and how large it is, then a zero-filled area (the BSS) and the address to start at; the sections follow. The processor is a PowerPC: the Gekko in the GameCube and the Broadway in the Wii, which decode the same instructions (with the paired singles); the rest of the instruction set is on the PowerPC pages.

A DOL has no signature. The explorer takes a file named .dol and checks its structure: every section that has a size lies inside the file and inside main memory, no two sections overlap, offsets are multiples of 32, there is a text section, and the entry point is inside one and a multiple of 4. A file that fails is shown as not a valid DOL. A DOL that has lost its extension is not recognised.

Structure

Every field is on the header page; how the sections are loaded is on sections; where they land and what else is in the address space is on memory map, and the registers a program reaches on hardware registers.

In the explorer

The viewer shows the header field by field, each section as a node of the file with its address and size, the sections and memory map as tables, and every text section disassembled with the PowerPC decoder, the entry point marked. Where an address built with lis and ori, addi or a load and store displacement lands on a hardware register, an OS global in low memory or a place in one of the file’s own sections, a note names it. The options are the processor (Gekko by default, Broadway for the Wii: the file does not say which console it is for), the values of the small data registers r13 and r2 (a DOL has no symbols, so nothing is assumed), register names and simplified mnemonics.

Not described

Known, not yet covered

• Reference: the way the disc’s apploader and the Wii’s IOS load a DOL (only the header rule WiiBrew states is given), the bit fields of every hardware register, the EXI and audio interface register lists, the DSP’s own instruction set, relocatable modules (REL) and the formats a game keeps beside its DOL (disc images, TPL textures, model and archive formats).
• Viewer: recognition by structure only (there is no signature); the header, the sections and the text sections disassembled from their load address; hardware, OS-global and own-section notes from lis sequences found by looking back at most 16 instructions (a guess about what the register holds at run time); no code and data separation, no symbols and no following of jumps; data sections are shown as bytes. It was checked only on built files, because no DOL exists on this machine, and has not been run in a browser by its author.

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