Add overlay patch to fix race condition in Kirby Super Star Ultra (#81)

arm9/source/Arm9Patcher.cpp

@@ -21,6 +21,7 @@
 #include "patches/arm9/OverlayPatches/DSProtectPatches/DSProtectOverlayPatch.h"
 #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/GoldenSunDarkDawn/GoldenSunDarkDawnOverlayHookPatch.h"
 #include "SecureSysCallsUnusedSpaceLocator.h"
 #include "fastSearch.h"
@@ -404,6 +405,15 @@ void Arm9Patcher::AddGameSpecificPatches(
             patchCollection.AddPatch(new NintendoDSGuideNandSavePatch());
             break;
         }
+        // Kirby Super Star Ultra
+        case GAMECODE("YKWE"):
+        case GAMECODE("YKWJ"):
+        case GAMECODE("YKWK"):
+        case GAMECODE("YKWP"):
+        {
+            overlayHookPatch->AddOverlayPatch(new KirbySuperStarUltraPatch());
+            break;
+        }
     }
 }
 

arm9/source/patches/arm9/OverlayPatches/KirbySuperStarUltra/KirbySuperStarUltraPatch.cpp

@@ -0,0 +1,41 @@
+#include "common.h"
+#include "gameCode.h"
+#include "patches/PatchContext.h"
+#include "KirbySuperStarUltraPatchAsm.h"
+#include "KirbySuperStarUltraPatch.h"
+
+const void* KirbySuperStarUltraPatch::InsertPatch(PatchContext& patchContext)
+{
+    kirbyultrapatch_nextAddress = next ? (const void*)next->InsertPatch(patchContext) : nullptr;
+
+    switch (patchContext.GetGameCode())
+    {
+        case GAMECODE("YKWE"):
+        {
+            kirbyultrapatch_offset = 0x63A8 + 0x160;
+            break;
+        }
+        case GAMECODE("YKWJ"):
+        {
+            kirbyultrapatch_offset = 0x6300 + 0x160;
+            break;
+        }
+        case GAMECODE("YKWK"):
+        {
+            kirbyultrapatch_offset = 0x63A8 + 0x160;
+            break;
+        }
+        case GAMECODE("YKWP"):
+        {
+            kirbyultrapatch_offset = 0x63F0 + 0x160;
+            break;
+        }
+    }
+
+    u32 patchSize = SECTION_SIZE(kirbyultrapatch);
+    void* patchAddress = patchContext.GetPatchHeap().Alloc(patchSize);
+    u32 entryAddress = (u32)&kirbyultrapatch_entry - (u32)SECTION_START(kirbyultrapatch) + (u32)patchAddress;
+    memcpy(patchAddress, SECTION_START(kirbyultrapatch), patchSize);
+
+    return (const void*)entryAddress;
+}

arm9/source/patches/arm9/OverlayPatches/KirbySuperStarUltra/KirbySuperStarUltraPatch.h

@@ -0,0 +1,39 @@
+#pragma once
+#include "../OverlayPatch.h"
+
+/// @brief Arm9 overlay patch for Kirby Super Star Ultra.
+/// @details
+/// This game has an issue where it softlocks on the corkboard screen after unlocking new items.
+/// This is caused by a race condition where it initializes a save write while it waits for
+/// 16 frames for an animation to complete. Normally, the save write finishes after the delay,
+/// but if it finishes before, as is common for a flashcart, it will get stuck waiting for
+/// the save write which has already completed.
+///
+/// The code for this is something like:
+///     if (SaveCompleteStatus() != 0 || CorkboardNewUnlocksContext->frameCounter < 16) return;
+///
+/// When it should be in the other order to short circuit properly:
+///     if (CorkboardNewUnlocksContext->frameCounter < 16 || SaveCompleteStatus() != 0) return;
+///
+/// To fix this, the two checks are swapped. This initial assembly:
+///     bl     SaveCompleteStatus
+///     cmp    r0, #0
+///     popne  {r4, pc}
+///     ldrb   r0, [r4, #0x50]
+///     cmp    r0, #0x10
+///     popcc  {r4, pc}
+///
+/// Is turned into this:
+///     ldrb   r0, [r4, #0x50]
+///     cmp    r0, #0x10
+///     popcc  {r4, pc}
+///     bl     SaveCompleteStatus
+///     cmp    r0, #0
+///     popne  {r4, pc}
+///
+/// (the offset for the bl also must be adjusted by 3 since it is PC-relative)
+class KirbySuperStarUltraPatch : public OverlayPatch
+{
+public:
+    const void* InsertPatch(PatchContext& patchContext) override;
+};

arm9/source/patches/arm9/OverlayPatches/KirbySuperStarUltra/KirbySuperStarUltraPatchAsm.h

@@ -0,0 +1,10 @@
+#pragma once
+#include "sections.h"
+
+DEFINE_SECTION_SYMBOLS(kirbyultrapatch);
+
+extern "C" void kirbyultrapatch_entry();
+
+extern u32 kirbyultrapatch_offset;
+
+extern const void* kirbyultrapatch_nextAddress;  // Next patch address

arm9/source/patches/arm9/OverlayPatches/KirbySuperStarUltra/KirbySuperStarUltraPatchAsm.s

@@ -0,0 +1,38 @@
+.cpu arm946e-s
+.syntax unified
+.section "kirbyultrapatch", "ax"
+.thumb
+
+.global kirbyultrapatch_entry
+.type kirbyultrapatch_entry, %function
+kirbyultrapatch_entry:
+    push {r4-r7, lr}
+    ldm r5!, {r0, r1} // ovy_id, ram_start
+    cmp r0, #6
+    bne continue_to_next
+
+    ldr r0, kirbyultrapatch_offset
+    adds r1, r0
+    ldm r1!, {r2, r3, r4, r5, r6, r7}
+    subs r1, #24 // Reset pointer
+    subs r2, #3 // Correct function call offset
+    stm r1!, {r5, r6, r7} // Swap the two blocks of 3 instructions
+    stm r1!, {r2, r3, r4}
+
+continue_to_next:
+    ldr r0, kirbyultrapatch_nextAddress
+    pop {r4-r7, pc}
+
+.balign 4
+
+.global kirbyultrapatch_offset
+kirbyultrapatch_offset:
+    .word 0
+
+.global kirbyultrapatch_nextAddress
+kirbyultrapatch_nextAddress:
+    .word 0
+
+.pool
+
+.end