Add overlay patch for hombrew AP in Rabbids Go Homeh (#82)

arm9/source/Arm9Patcher.cpp

@@ -22,6 +22,7 @@
 #include "patches/arm9/OverlayPatches/DSProtectPatches/DSProtectPuyoPuyo7Patch.h"
 #include "patches/arm9/OverlayPatches/PokemonIr/PokemonIrApPatch.h"
 #include "patches/arm9/OverlayPatches/KirbySuperStarUltra/KirbySuperStarUltraPatch.h"
+#include "patches/arm9/OverlayPatches/RabbidsGoHome/RabbidsGoHomePatch.h"
 #include "patches/arm9/OverlayPatches/GoldenSunDarkDawn/GoldenSunDarkDawnOverlayHookPatch.h"
 #include "SecureSysCallsUnusedSpaceLocator.h"
 #include "fastSearch.h"
@@ -405,6 +406,13 @@ void Arm9Patcher::AddGameSpecificPatches(
             patchCollection.AddPatch(new NintendoDSGuideNandSavePatch());
             break;
         }
+        // Rabbids Go Home
+        case GAMECODE("VRGE"):
+        case GAMECODE("VRGV"):
+        {
+            overlayHookPatch->AddOverlayPatch(new RabbidsGoHomePatch());
+            break;
+        }
         // Kirby Super Star Ultra
         case GAMECODE("YKWE"):
         case GAMECODE("YKWJ"):

arm9/source/patches/arm9/OverlayPatches/RabbidsGoHome/RabbidsGoHomePatch.cpp

@@ -0,0 +1,31 @@
+#include "common.h"
+#include "gameCode.h"
+#include "patches/PatchContext.h"
+#include "RabbidsGoHomePatchAsm.h"
+#include "RabbidsGoHomePatch.h"
+
+const void* RabbidsGoHomePatch::InsertPatch(PatchContext& patchContext)
+{
+    rabbidspatch_nextAddress = next ? (const void*)next->InsertPatch(patchContext) : nullptr;
+
+    switch (patchContext.GetGameCode())
+    {
+        case GAMECODE("VRGE"):
+        {
+            rabbidspatch_offset = 0x1465C + 0x1C;
+            break;
+        }
+        case GAMECODE("VRGV"):
+        {
+            rabbidspatch_offset = 0x146A4 + 0x1C;
+            break;
+        }
+    }
+
+    u32 patchSize = SECTION_SIZE(rabbidspatch);
+    void* patchAddress = patchContext.GetPatchHeap().Alloc(patchSize);
+    u32 entryAddress = (u32)&rabbidspatch_entry - (u32)SECTION_START(rabbidspatch) + (u32)patchAddress;
+    memcpy(patchAddress, SECTION_START(rabbidspatch), patchSize);
+
+    return (const void*)entryAddress;
+}

arm9/source/patches/arm9/OverlayPatches/RabbidsGoHome/RabbidsGoHomePatch.h

@@ -0,0 +1,17 @@
+#pragma once
+#include "../OverlayPatch.h"
+
+/// @brief Arm9 overlay patch for Rabbids Go Home.
+/// @details
+/// This game has a homebrew AP method based on ROM read timings. Specifically, it will
+/// run 100 ROM reads of 0x4000 bytes each, or 32 0x200-byte pages, and use ticks to time how
+/// long it takes. It must take between 0x80000 and 0x88000 ticks, or 1.001 to 1.063 seconds,
+/// or the game will hang prior to the title screen (after the publisher splash and language selection).
+/// The actual contents of the ROM reads are not checked, and they are obtained using TWL SDK CARD_ReadRom.
+///
+/// To bypass this, most of the function that runs the AP check is skipped, as it has no other side effects.
+class RabbidsGoHomePatch : public OverlayPatch
+{
+public:
+    const void* InsertPatch(PatchContext& patchContext) override;
+};

arm9/source/patches/arm9/OverlayPatches/RabbidsGoHome/RabbidsGoHomePatchAsm.h

@@ -0,0 +1,10 @@
+#pragma once
+#include "sections.h"
+
+DEFINE_SECTION_SYMBOLS(rabbidspatch);
+
+extern "C" void rabbidspatch_entry();
+
+extern u32 rabbidspatch_offset;
+
+extern const void* rabbidspatch_nextAddress;  // Next patch address

arm9/source/patches/arm9/OverlayPatches/RabbidsGoHome/RabbidsGoHomePatchAsm.s

@@ -0,0 +1,34 @@
+.cpu arm946e-s
+.syntax unified
+.section "rabbidspatch", "ax"
+.thumb
+
+.global rabbidspatch_entry
+.type rabbidspatch_entry, %function
+rabbidspatch_entry:
+    push {r5,lr}
+    ldm r5!, {r0, r1} // ovy_id, ram_start
+    cmp r0, #1
+    bne continue_to_next
+
+    ldr r2, rabbidspatch_offset
+    ldr r0, =0xE3A00001  // mov r0, #1
+    str r0, [r1, r2]
+
+continue_to_next:
+    ldr r0, rabbidspatch_nextAddress
+    pop {r5,pc}
+
+.balign 4
+
+.global rabbidspatch_offset
+rabbidspatch_offset:
+    .word 0
+
+.global rabbidspatch_nextAddress
+rabbidspatch_nextAddress:
+    .word 0
+
+.pool
+
+.end