Decompiling retail versions

The next decompilation target for OOT is the PAL GameCube Master Quest ROM (gc-eu-mq), because it is the retail version that is most similar to the Debug ROM. Unfortunately there are still a lot of differences, many of which are register or stack allocation differences because retail ROMs were built with different compiler flags. However, once this version is done, future retail versions should be much easier, as the changes between retail versions are small in comparison.

Instead of comparing against a matching build, the target ROM is disassembled and recompiled as relocatable .o files directly into expected/build/gc-eu-mq for diff tools. This allows us to make progress matching code in parallel with solving other problems (such as the build system, ROM organization, and BSS ordering). The files in tools/disasm/gc-eu-mq say how to split the source files and where the functions and variables are in the target ROM, and these may need to be updated if there are mistakes or if function names change due to documentation work.

Unfortunately, the disassembly is not perfect, so a "correct" decompilation might still show diffs with data symbols. We might improve this later, but these data diffs are fine to ignore for now.

We can disable code that was removed in retail builds by adding #ifdef OOT_DEBUG around these parts of the code. In order too keep the code readable, we should try to minimize the amount of #ifdef noise whenever possible. For example, instead of writing

void foo() {
#ifdef OOT_DEBUG
    if (condition || SREG(0)) {
#else
    if (condition) {
#endif
        bar();
    }

#ifdef OOT_DEBUG
    if (condition || SREG(0)) {
#else
    if (condition) {
#endif
        baz();
    }
}

consider something like this instead:

#ifdef OOT_DEBUG
#define CONDITION (condition || SREG(0))
#else
#define CONDITION (condition)
#endif

void foo() {
    if (CONDITION) {
        bar();
    }

    if (CONDITION) {
        baz();
    }
}

Setup

Copy your target PAL GameCube Master Quest ROM (non-debug) to baseroms/gc-eu-mq/baserom.z64
Extract assets and ROM files from the Debug ROM by running
```
make setup -jN
```
if necessary.
Build the non-matching test ROM by running
```
make setup -jN VERSION=gc-eu-mq
make -jN VERSION=gc-eu-mq
```
where N is the number of cores on your machine. This will build into build/gc-eu-mq and produce oot-gc-eu-mq.z64.

If you later want to delete all output files, run
```
make clean VERSION=gc-eu-mq
```
Disassemble the target ROM by running
```
make disasm -jN VERSION=gc-eu-mq
```
where N is the number of cores on your machine. The outputs will be written to expected/build/gc-eu-mq.

Note that if you need to copy a matching build for the Debug ROM, you can use
```
mkdir -p expected/build
cp -r build/gc-eu-mq-dbg expected/build
```
to avoid clobbering the disassembly.

Diff Tools

retail_progress.py

Running ./retail_progress.py file.c will attempt to figure out which functions in a file still need to match for gc-eu-mq. To get an overview of diffs for all files, run ./retail_progress.py with no arguments.

asm-differ / diff.py

To diff assembly for a single function in gc-eu-mq, run e.g.

./diff.py -mwo3 -v gc-eu-mq Math3D_CylTriVsIntersect

The -v flag tells diff.py to compare between build/gc-eu-mq and expected/build/gc-eu-mq, and to use make VERSION=gc-eu-mq when rebuilding.

You may also want to diff the Debug ROM in another terminal with

./diff.py -mwo3 Math3D_CylTriVsIntersect

to ensure any changes still match there.

Permuter and decomp.me

Disassembly for individual functions is written to expected/build/gc-eu-mq/functions, so to get a decomp.me scratch you can run e.g.

decomp-permuter/import.py \
  src/code/sys_math3d.c \
  expected/build/gc-eu-mq/functions/src/code/sys_math3d/Math3D_CylTriVsIntersect.s \
  VERSION=gc-eu-mq --decompme

4 KiB Raw Blame History