75 lines
4.6 KiB
Markdown
75 lines
4.6 KiB
Markdown
# Other approaches
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## Manual assembly
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With existing GameCube/Wii decompilation tooling, the setup process is very tedious and error-prone.
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The general process is:
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- Begin by disassembling the original binary with a tool like
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[doldisasm.py](https://gist.github.com/camthesaxman/a36f610dbf4cc53a874322ef146c4123). This produces one giant
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assembly file per section.
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- Manually comb through the assembly files and fix many issues, like incorrect or missing relocations, incorrect or
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missing symbols, and more.
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- Manually find-and-replace the auto-generated symbol names based on other sources, like other decompilation projects
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or a map file. (If you're lucky enough to have one)
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- Manually determine data types and sizes, and convert them accordingly. (For example, `.4byte` -> `.float`, strings,
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etc)
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- Manually split the assembly files into individual objects. This is a very tedious process, as it requires identifying
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the boundaries of each function, determining whether adjacent functions are related, finding associated
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data from each data section, and cut-and-pasting all of this into a new file.
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Other downsides of this approach:
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- Manually editing the assembly means that the result is not reproducible. You can't run the script again to
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make any updates, because your changes will be overwritten. This also means that the assembly files must be
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stored in version control, which is not ideal.
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- Incorrectly splitting objects is very easy to do, and can be difficult to detect. For example, a `.ctors` entry _must_
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be located in the same object as the function it references, otherwise the linker will not generate the correct
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`.ctors` entry. `extab` and `extabindex` entries _must also_ be located in the same object as the function they
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reference, have a label and have the correct size, and have a direct relocation rather than a section-relative
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relocation. Otherwise, the linker will crash with a cryptic error message.
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- Relying on assembly means that you need an assembler. For GameCube/Wii, this means devkitPro, which is a
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large dependency and an obstacle for new contributors. The assembler also has some quirks that don't interact well
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with `mwldeppc`, which means that the object files must be manually post-processed to fix these issues. (See the
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[elf fixup](/README.md#elf-fixup) command)
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With decomp-toolkit:
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- Many analysis steps are automated and highly accurate. Many DOL files can be analyzed and split into re-linkable
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objects with no configuration.
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- Signature analysis automatically labels common functions and objects, and allows for more accurate relocation
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rebuilding.
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- Any manual adjustments are stored in configuration files, which are stored in version control.
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- Splitting is simplified by updating a configuration file. The analyzer will check for common issues, like
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incorrectly split `.ctors`/`.dtors`/`extab`/`extabindex` entries. If the user hasn't configured a split for these,
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the analyzer will automatically split them along with their associated functions to ensure that the linker will
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generate everything correctly. This means that matching code can be written without worrying about splitting all
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sections up front.
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- The splitter generates object files directly, with no assembler required. This means that we can avoid the devkitPro
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requirement. (Although we can still generate assembly files for viewing, editing, and compatibility with other tools)
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## dadosod
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[dadosod](https://github.com/InusualZ/dadosod) is a newer replacement for `doldisasm.py`. It has more accurate function
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and relocation analysis than `doldisasm.py`, as well as support for renaming symbols based on a map file. However, since
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it operates as a one-shot assembly generator, it still suffers from many of the same issues described above.
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## ppcdis
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[ppcdis](https://github.com/SeekyCt/ppcdis) is one of the tools that inspired decomp-toolkit. It has more accurate
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analysis than doldisasm.py, and has similar goals to decomp-toolkit. It's been used successfully in several
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decompilation projects.
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However, decomp-toolkit has a few advantages:
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- Faster and more accurate analysis. (See [Analyzer features](/README.md#analyzer-features))
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- Emits object files directly, with no assembler required.
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- More robust handling of features like common BSS, `.ctors`/`.dtors`/`extab`/`extabindex`, and more.
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- Requires very little configuration to start.
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- Automatically labels common functions and objects with signature analysis.
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## Honorable mentions
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[splat](https://github.com/ethteck/splat) is a binary splitting tool for N64 and PSX. Some ideas from splat inspired
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decomp-toolkit, like the symbol configuration format.
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