Preprocess cheats to get rid of hacks that try to modify the cheat engine, add support for C2 cheat opcode

arm7/source/loader/CheatPreprocessor.cpp

@@ -0,0 +1,80 @@
+#include "common.h"
+#include <iterator>
+#include <algorithm>
+#include <span>
+#include "CheatPreprocessor.h"
+
+// Based on original code by edo9300: https://github.com/edo9300/nitrohax-usercheat-supercard/blob/master/arm9/source/cheat.cpp.
+
+static constexpr u64 NOP = 0x00000000D4000000;
+static constexpr u64 D4_ORR_HACK = 0xE1833004023FE424;
+static constexpr u64 D4_AND_HACK = 0xE0033004023FE424;
+static constexpr u64 D4_ADD_HACK = 0xE0833004023FE424;
+static constexpr u64 DB_CODE_FIX_HACK = 0x0A000003023FE4D8;
+
+// Make 0x0E handler execute the data as arm
+static constexpr u64 ASM_HACK_START = 0x012FFF11023FE074;
+// Restore behaviour of 0x0E handler
+static constexpr u64 ASM_HACK_END = 0xE3520003023FE074;
+
+void CheatPreprocessor::PreprocessCheat(pload_cheat_t* cheat) const
+{
+    PatchD4Hack(cheat, D4_ORR_HACK, 0x1);
+    PatchD4Hack(cheat, D4_AND_HACK, 0x2);
+    PatchD4Hack(cheat, D4_ADD_HACK, 0x0);
+    PatchDBFix(cheat);
+    PatchAsmHack(cheat);
+}
+
+void CheatPreprocessor::PatchD4Hack(pload_cheat_t* cheat, u64 hackPattern, u8 patchedInstructionFlag) const
+{
+    std::span<u64> u64Data((u64*)cheat->opcodes, cheat->length / sizeof(u64));
+    auto start = std::ranges::find(u64Data, hackPattern);
+    if (start != u64Data.end())
+    {
+        *start++ = NOP;
+        auto end = std::find(start, u64Data.end(), D4_ADD_HACK);
+        auto it = std::find_if(start, end, [] (auto elem) { return (elem & 0xFFFFFFFF) == 0xD4000000; });
+        if (it != end)
+        {
+            // Replace 0xD4 code with nitrohax's custom operator code
+            *it |= patchedInstructionFlag;
+        }
+        if (end != u64Data.end())
+        {
+            *end++ = NOP;
+        }
+    }
+}
+
+void CheatPreprocessor::PatchDBFix(pload_cheat_t* cheat) const
+{
+    std::span<u64> u64Data((u64*)cheat->opcodes, cheat->length / sizeof(u64));
+    auto start = std::ranges::find(u64Data, DB_CODE_FIX_HACK);
+    if (start != u64Data.end())
+    {
+        *start++ = NOP;
+    }
+}
+
+void CheatPreprocessor::PatchAsmHack(pload_cheat_t* cheat) const
+{
+    // Make the asm cheats designed for ards work with nitrohax
+    std::span<u64> u64Data((u64*)cheat->opcodes, cheat->length / sizeof(u64));
+    auto start = std::ranges::find(u64Data, ASM_HACK_START);
+    if (start != u64Data.end())
+    {
+        *start++ = NOP;
+        auto end = std::find(start, u64Data.end(), ASM_HACK_END);
+        auto it = std::find_if(start, end, [] (auto elem) { return (elem & 0xFFFFFFFF) == 0xE0000000; });
+        if (it != end)
+        {
+            // Replace 0x0E code with nitrohax's 0xC2 in arm mode (0xXXXXXXXXE0000000 - 0xXXXXXXXX1E000000 = 0xXXXXXXXXC2000000)
+            *it -= 0x1E000000;
+        }
+        if (end != u64Data.end())
+        {
+            *end++ = NOP;
+        }
+    }
+}

arm7/source/loader/CheatPreprocessor.h

@@ -0,0 +1,16 @@
+#pragma once
+#include "../../include/picoLoader7.h"
+
+/// @brief Class for preprocessing cheats to get rid of hacks that try to modify the cheat engine.
+class CheatPreprocessor
+{
+public:
+    /// @brief Preprocesses the given \p cheat.
+    /// @param cheat The cheat to preprocess.
+    void PreprocessCheat(pload_cheat_t* cheat) const;
+
+private:
+    void PatchD4Hack(pload_cheat_t* cheat, u64 hackPattern, u8 patchedInstructionFlag) const;
+    void PatchDBFix(pload_cheat_t* cheat) const;
+    void PatchAsmHack(pload_cheat_t* cheat) const;
+};

arm7/source/loader/NdsLoader.cpp

@@ -27,6 +27,7 @@
 #include "DSMode.h"
 #include "Arm7IoRegisterClearer.h"
 #include "PatchListFactory.h"
+#include "CheatPreprocessor.h"
 #include "NdsLoader.h"
 
 #define AP_LIST_PATH      "/_pico/aplist.bin"
@@ -523,6 +524,7 @@ void NdsLoader::ApplyArm7Patches()
 {
     sendToArm9(IPC_COMMAND_ARM9_APPLY_ARM7_PATCHES);
     sendToArm9(_cheats ? _cheats->length : 0);
+    PreprocessCheats();
     void* patchSpaceStart = (void*)receiveFromArm9();
     void* cheatsPtr = (void*)receiveFromArm9();
     if (cheatsPtr != nullptr && _cheats != nullptr)
@@ -569,6 +571,20 @@ void NdsLoader::ApplyArm7Patches()
     }
 }
 
+void NdsLoader::PreprocessCheats()
+{
+    if (_cheats != nullptr)
+    {
+        CheatPreprocessor cheatPreprocessor;
+        auto cheat = &_cheats->firstCheat;
+        for (u32 i = 0; i < _cheats->numberOfCheats; i++)
+        {
+            cheatPreprocessor.PreprocessCheat(cheat);
+            cheat = (pload_cheat_t*)((u8*)cheat + cheat->length);
+        }
+    }
+}
+
 void NdsLoader::SetupSharedMemory(u32 cardId, u32 agbMem, u32 resetParam, u32 romOffset, u32 bootType)
 {
     memcpy(TWL_SHARED_MEMORY->ntrSharedMem.cardRomHeader, &_romHeader, sizeof(nds_header_ntr_t) - 0x10);

arm7/source/loader/NdsLoader.h

@@ -1,5 +1,6 @@
 #pragma once
 #include "common.h"
+#include "../../include/picoLoader7.h"
 #include "ndsHeader.h"
 #include "DsiWareSaveArranger.h"
 #include "BootMode.h"
@@ -44,7 +45,7 @@ public:
 
     /// @brief Sets the cheats to apply to the rom.
     /// @param cheats The cheats.
-    void SetCheats(const pload_cheats_t* cheats)
+    void SetCheats(pload_cheats_t* cheats)
     {
         _cheats = cheats;
     }
@@ -60,12 +61,13 @@ private:
     const TCHAR* _launcherPath = nullptr;
     u32 _argumentsLength = 0;
     const char* _arguments = nullptr;
-    const pload_cheats_t* _cheats = nullptr;
+    pload_cheats_t* _cheats = nullptr;
     nds_header_twl_t _romHeader;
     DsiWareSaveResult _dsiwareSaveResult;
 
     bool IsCloneBootRom(u32 romOffset);
     void ApplyArm7Patches();
+    void PreprocessCheats();
     void SetupSharedMemory(u32 cardId, u32 agbMem, u32 resetParam, u32 romOffset, u32 bootType);
     void LoadFirmwareUserSettings();
     bool ShouldAttemptDldiPatch();

arm9/source/patches/arm7/cheats/CheatEnginePatchCode.s

@@ -98,10 +98,13 @@ runCheat_opcode_loop:
     bcs 1f // if set, the opcode is executed
 
     lsrs r3, r1, #24 // r3 = op
+    cmp r3, #0xC2
+    beq 2f
     cmp r3, #0xE0
     bne runCheat_opcode_loop
 
-    // opcode E has a dynamic length
+2:
+    // opcode C2 and EX have a dynamic length
     adds r2, #7
     movs r3, #7
     bics r2, r3 // pad length to multiple of 8
@@ -229,6 +232,8 @@ opcode_CX:
     lsrs r3, r1, #24 // r3 = op
     cmp r3, #0
     beq opcode_C0
+    cmp r3, #2
+    beq opcode_C2
     cmp r3, #4
     beq opcode_C4
     cmp r3, #5
@@ -243,6 +248,26 @@ opcode_C0: // FOR 0..b
     mov r10, r7 // condition stack backup
     b runCheat_opcode_loop
 
+opcode_C2: // execute code from cheat list
+    movs r3, r0
+
+    // pad length to multiple of 8
+    adds r2, r2, #7
+    lsrs r2, r2, #3
+    lsls r2, r2, #3
+    adds r0, r2
+
+    lsrs r1, r1, #1
+    bcc 1f
+    adds r3, #1 // set thumb bit
+1:
+    push {r0}
+    bl 2f
+    pop {r0}
+    b runCheat_opcode_loop
+2:
+    bx r3
+
 opcode_C4: // offset = pointer to C4000000 opcode
     movs r5, r0
     subs r5, #8