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149 lines
3.8 KiB
Markdown
149 lines
3.8 KiB
Markdown
# Decompiling retail versions
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The next decompilation target for OOT is the PAL GameCube Master Quest ROM
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(`gc-eu-mq`), because it is the retail version that is most similar to the Debug
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ROM. Unfortunately there are still a lot of differences, many of which are
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register or stack allocation differences because retail ROMs were built with
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different compiler flags. However, once this version is done, future
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retail versions should be much easier, as the changes between retail versions are
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small in comparison.
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Instead of comparing against a matching build, the target ROM is disassembled
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and recompiled as relocatable `.o` files directly into `expected/build/gc-eu-mq`
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for diff tools. This allows us to make progress matching code in parallel with
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solving other problems (such as the build system, ROM organization, and BSS
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ordering). The files in `tools/disasm/gc-eu-mq` say how to split the source
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files and where the functions and variables are in the target ROM, and these may
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need to be updated if there are mistakes or if function names change due to
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documentation work.
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Unfortunately, the disassembly is not perfect, so a "correct" decompilation might
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still show diffs with data symbols. We might improve this later, but these data
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diffs are fine to ignore for now.
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We can disable code that was removed in retail builds by adding
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`#ifdef OOT_DEBUG` around these parts of the code. In order too keep the code
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readable, we should try to minimize the amount of `#ifdef` noise whenever
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possible. For example, instead of writing
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```c
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void foo() {
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#ifdef OOT_DEBUG
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if (condition || SREG(0)) {
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#else
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if (condition) {
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#endif
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bar();
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}
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#ifdef OOT_DEBUG
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if (condition || SREG(0)) {
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#else
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if (condition) {
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#endif
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baz();
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}
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}
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```
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consider something like this instead:
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```c
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#ifdef OOT_DEBUG
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#define CONDITION (condition || SREG(0))
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#else
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#define CONDITION (condition)
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#endif
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void foo() {
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if (CONDITION) {
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bar();
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}
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if (CONDITION) {
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baz();
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}
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}
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```
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## Setup
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1. Copy your target PAL GameCube Master Quest ROM (non-debug) to
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`baseroms/gc-eu-mq/baserom.z64`
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1. Extract assets and ROM files from the Debug ROM by running
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```sh
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make setup -jN
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```
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if necessary.
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1. Build the non-matching test ROM by running
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```sh
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make setup -jN VERSION=gc-eu-mq
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make -jN VERSION=gc-eu-mq
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```
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where `N` is the number of cores on your machine. This will build into
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`build/gc-eu-mq` and produce `oot-gc-eu-mq.z64`.
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If you later want to delete all output files, run
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```sh
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make clean VERSION=gc-eu-mq
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```
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1. Disassemble the target ROM by running
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```sh
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make disasm -jN VERSION=gc-eu-mq
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```
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where `N` is the number of cores on your machine. The outputs will be written to
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`expected/build/gc-eu-mq`.
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Note that if you need to copy a matching build for the Debug ROM, you can use
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```sh
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mkdir -p expected/build
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cp -r build/gc-eu-mq-dbg expected/build
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```
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to avoid clobbering the disassembly.
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## Diff Tools
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### asm-differ / diff.py
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To diff assembly for a single function in `gc-eu-mq`, run e.g.
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```sh
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./diff.py -mwo3 -v gc-eu-mq Math3D_CylTriVsIntersect
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```
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The `-v` flag tells `diff.py` to compare between `build/gc-eu-mq` and
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`expected/build/gc-eu-mq`, and to use `make VERSION=gc-eu-mq` when rebuilding.
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You may also want to diff the Debug ROM in another terminal with
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```sh
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./diff.py -mwo3 Math3D_CylTriVsIntersect
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```
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to ensure any changes still match there.
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### Permuter and decomp.me
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Disassembly for individual functions is written to
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`expected/build/gc-eu-mq/functions`, so to get a [decomp.me](https://decomp.me/) scratch you can run
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e.g.
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```sh
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decomp-permuter/import.py \
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src/code/sys_math3d.c \
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expected/build/gc-eu-mq/functions/src/code/sys_math3d/Math3D_CylTriVsIntersect.s \
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VERSION=gc-eu-mq --decompme
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```
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