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Update CONTRIBUTING.md
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@ -83,11 +83,10 @@ Then, start translating the code to `src/evilSpirit.c`, bit by bit:
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adds r4, r0, #0
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```
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```c
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void sub_08086284(u8 *r4) {
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void sub_08086284(u8* r0) {
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```
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---
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```asm
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add r4, r0, #0
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ldr r1, _080862B4 @ =gUnk_08120668
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ldrb r0, [r4, #0xc]
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lsl r0, r0, #0x2
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@ -97,7 +96,7 @@ Then, start translating the code to `src/evilSpirit.c`, bit by bit:
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bl _call_via_r1
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```
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```c
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gUnk_08120668[*(u8 *)(r4 + 12)](r4);
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gUnk_08120668[*(u8 *)(r0 + 0xc)](r0);
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```
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---
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@ -109,7 +108,7 @@ Then, start translating the code to `src/evilSpirit.c`, bit by bit:
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strb r0, [r1]
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```
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```c
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*(u8 *)(r4 + 65) = 0;
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*(u8 *)(r0 + 0x41) = 0;
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```
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---
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```asm
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@ -123,7 +122,7 @@ Then, start translating the code to `src/evilSpirit.c`, bit by bit:
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bl sub_0805EC9C
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```
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```c
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sub_0805EC9C(r4, *(u16 *)(r4 + 118), *(u16 *)(r4 + 122), 0);
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sub_0805EC9C(r0, *(u16 *)(r0 + 0x76), *(u16 *)(r0 + 0x7a), 0);
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```
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---
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```asm
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@ -132,10 +131,14 @@ Then, start translating the code to `src/evilSpirit.c`, bit by bit:
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```c
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return;
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```
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The type signature of the function depends on the return type.
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* `pop {r4, pc}`: `void`
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The type signature of the function depends on the return type. Return values are stored in r0,
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so pay attention to how the assembly treats this register toward the end of the function.
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ex:
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* `add r0, r4, #0`
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`pop {r4, pc}`: `void`, `*`
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`pop {r4, pc}`
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The compiler chose to move a value into r0 here; the most likely explanation is that it's returning something.
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You will need to look at the caller and the function prologue to determine the exact type if not void.
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@ -145,11 +148,10 @@ Since it only used `pop {r4, pc}`, it's probably `void`.
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Putting it all together, we get:
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```c
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void sub_08086284(u8 *r4) {
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{
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gUnk_08120668[*(u8 *)(r4 + 12)](r4);
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*(u8 *)(r4 + 65) = 0;
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sub_0805EC9C(r4, *(u16 *)(r4 + 118), *(u16 *)(r4 + 122), 0);
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void sub_08086284(u8 *r0) {
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gUnk_08120668[*(u8 *)(r0 + 0xc)](r0);
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*(u8 *)(r0 + 0x41) = 0;
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sub_0805EC9C(r0, *(u16 *)(r0 + 0x76), *(u16 *)(r0 + 0x7a), 0);
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return;
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}
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```
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@ -160,10 +162,10 @@ void sub_08086284(u8 *r4) {
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This line doesn't look quite right.
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```c
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gUnk_08120668[*(u8 *)(r4 + 12)](r4);
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gUnk_08120668[*(u8 *)(r0 + 0xc)](r0);
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```
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What is `r4`? Since this function corresponds to an entity, we should first try to assign r4 to an`Entity` struct.
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What is `r0`? Since this function corresponds to an entity, we should first try to assign r0 to an `Entity` struct.
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You can find out what this is with `git grep`:
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```sh
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@ -176,39 +178,35 @@ include/entity.h:typedef struct Entity
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So it's a struct called `Entity`. Let's look in `entity.h`:
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```c
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typedef struct Entity
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{
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u32 *field_0x0;
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u32 * field_0x4;
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EntityType entityType;
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u8 action;
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u8 subAction;
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u8 actionDelay;
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u8 field_0xf;
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u8 flags;
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typedef struct Entity_ {
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/*0x00*/ struct Entity_* prev;
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/*0x04*/ struct Entity_* next;
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/*0x08*/ u8 kind;
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/*0x09*/ u8 id;
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/*0x0a*/ u8 type;
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/*0x0b*/ u8 type2;
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/*0x0c*/ u8 action;
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/*0x0d*/ u8 subAction;
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...
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} Entity;
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```
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---
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What's the 12th byte in this struct?
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```c
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u32 *field_0x0; //0-3
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u32 * field_0x4; //4-7
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EntityType entityType; //8-11
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u8 action; //12
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u8 subAction; //13
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/*0x00*/ struct Entity_* prev;
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/*0x04*/ struct Entity_* next;
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...
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/*0x0c*/ u8 action; <-
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```
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---
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The 12th byte belongs to `action`. We can substitute this in by replacing r4's parameter type and adding in the member names.
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The 12th byte belongs to `action`. We can substitute this in by replacing r0's parameter type and adding in the member names.
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```c
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void sub_08086284(Entity *r4) {
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gUnk_08120668[r4->action](r4);
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void sub_08086284(Entity *r0) {
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gUnk_08120668[r0->action](r0);
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```
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Much better.
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@ -216,35 +214,33 @@ Much better.
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---
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```c
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void sub_08086284(Entity *r4) {
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gUnk_08120668[r4->action](r4);
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r4->bitfield = 0;
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sub_0805EC9C(r4, *((u16 *)&r4->heldObjectPtr + 1), r4->field_0x7a, 0);
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void sub_08086284(Entity *r0) {
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gUnk_08120668[r0->action](r0);
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r0->bitfield = 0;
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sub_0805EC9C(r0, r0->field_0x76.HWORD, r0->field_0x7a.HWORD, 0);
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return;
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}
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```
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The second of the function that is called uses an offset right in the middle of `heldObjectPtr`. Something seems wrong.
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We can ignore this for now, since we can come back to that later.
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Right now we are just concerned with making the function match, even if it isn't pretty.
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The fields at the end of of `Entity` are general purpose. For this reason the fields are defined as unions so the proper data size may be loaded.
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This isn't pretty, but right now we are just concerned with making the function match. Later on we can define these entity-specific fields.
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## 5. Build
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```sh
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make
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```
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```gcc
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```
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src/evilSpirit.c: In function `sub_08086284':
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src/evilSpirit.c:5: `r4' undeclared (first use in this function)
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src/evilSpirit.c:4: syntax error before `*'
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src/evilSpirit.c:5: `gUnk_08120668' undeclared (first use in this function)
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src/evilSpirit.c:5: (Each undeclared identifier is reported only once for each function it appears in.)
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src/evilSpirit.c:7: warning: implicit declaration of function `sub_0805EC9C'
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```
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We got some errors. We need to tell the compiler what `gUnk_08120668`, `r4`, and `sub_0805EC9C` are.
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We got some errors. We need to tell the compiler what `gUnk_08120668`, `Entity`, and `sub_0805EC9C` are.
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We know `r4` is an `Entity`, which is from `entity.h`. We can declare this above the function:
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We know `r0` is an `Entity`, which is from `entity.h`. We can declare this above the function:
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```c
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#include "entity.h"
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```
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@ -265,10 +261,10 @@ Now our file looks like this:
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extern void sub_0805EC9C();
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extern void (*gUnk_08120668[])(Entity *);
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void sub_08086284(Entity *r4) {
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gUnk_08120668[r4->action](r4);
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r4->bitfield = 0;
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sub_0805EC9C(r4, *((u16 *)&r4->heldObjectPtr + 1), r4->field_0x7a, 0);
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void sub_08086284(Entity *r0) {
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gUnk_08120668[r0->action](r0);
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r0->bitfield = 0;
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sub_0805EC9C(r0, r0->field_0x76.HWORD, r0->field_0x7a.HWORD, 0);
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return;
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}
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```
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