GeckoCode: Use named constants in ICache flush hack

Turns out one of the magic numbers was very magic. The gameid is
an ad-hoc comm protocol with HLE_Misc to control the number of times
the ICache is reset.

Source/Core/Core/Boot/Boot.cpp

@@ -17,6 +17,7 @@
 #include "Core/ConfigManager.h"
 #include "Core/Core.h"
 #include "Core/Debugger/Debugger_SymbolMap.h"
+#include "Core/GeckoCode.h"
 #include "Core/HLE/HLE.h"
 #include "Core/HW/DVDInterface.h"
 #include "Core/HW/EXI_DeviceIPL.h"
@@ -481,6 +482,6 @@ bool CBoot::BootUp()
 
   // Not part of the binary itself, but either we or Gecko OS might insert
   // this, and it doesn't clear the icache properly.
-  HLE::Patch(0x800018a8, "GeckoCodehandler");
+  HLE::Patch(Gecko::ENTRY_POINT, "GeckoCodehandler");
   return true;
 }

Source/Core/Core/GeckoCode.cpp

@@ -18,10 +18,8 @@
 
 namespace Gecko
 {
-static constexpr u32 INSTALLER_BASE_ADDRESS = 0x80001800;
 static constexpr u32 INSTALLER_END_ADDRESS = 0x80003000;
 static constexpr u32 CODE_SIZE = 8;
-static constexpr u32 MAGIC_GAMEID = 0xD01F1BAD;
 
 // return true if a code exists
 bool GeckoCode::Exist(u32 address, u32 data) const
@@ -102,6 +100,7 @@ static bool InstallCodeHandlerLocked()
   const u32 codelist_end_address = INSTALLER_END_ADDRESS;
 
   // Write a magic value to 'gameid' (codehandleronly does not actually read this).
+  // This value will be read back and modified over time by HLE_Misc::HLEGeckoCodehandler.
   PowerPC::HostWrite_U32(MAGIC_GAMEID, INSTALLER_BASE_ADDRESS);
 
   // Create GCT in memory
@@ -161,7 +160,7 @@ void RunCodeHandler()
   if (s_active_codes.empty())
     return;
 
-  if (!s_code_handler_installed || PowerPC::HostRead_U32(INSTALLER_BASE_ADDRESS) - MAGIC_GAMEID > 5)
+  if (!s_code_handler_installed)
   {
     s_code_handler_installed = InstallCodeHandlerLocked();
 
@@ -175,7 +174,7 @@ void RunCodeHandler()
   // the original return address (which will still be in the link register) at the end.
   if (PC == LR)
   {
-    PC = NPC = INSTALLER_BASE_ADDRESS + 0xA8;
+    PC = NPC = ENTRY_POINT;
   }
 }
 

Source/Core/Core/GeckoCode.h

@@ -33,6 +33,20 @@ public:
   bool Exist(u32 address, u32 data) const;
 };
 
+// Installation address for codehandler.bin in the Game's RAM
+constexpr u32 INSTALLER_BASE_ADDRESS = 0x80001800;
+constexpr u32 ENTRY_POINT = 0x800018A8;
+
+// This forms part of a communication protocol with HLE_Misc::HLEGeckoCodehandler.
+// Basically, codehandleronly.s doesn't use ICBI like it's supposed to when patching the
+// game's code. This results in the JIT happily ignoring all code patches for blocks that
+// are already compiled. The hack for getting around that is that the first 5 frames after
+// the handler is installed (0xD01F1BAD -> +5 -> 0xD01F1BB2) cause full ICache resets.
+//
+// HLEGeckoCodehandler will increment this value 5 times then cease flushing the ICache to
+// preserve the emulation performance.
+constexpr u32 MAGIC_GAMEID = 0xD01F1BAD;
+
 void SetActiveCodes(const std::vector<GeckoCode>& gcodes);
 void RunCodeHandler();
 

Source/Core/Core/HLE/HLE_Misc.cpp

@@ -7,6 +7,7 @@
 
 #include "Common/CommonTypes.h"
 #include "Core/ConfigManager.h"
+#include "Core/GeckoCode.h"
 #include "Core/HLE/HLE_Misc.h"
 #include "Core/HW/CPU.h"
 #include "Core/Host.h"
@@ -47,17 +48,17 @@ void HLEGeckoCodehandler()
   // been read into memory, or such, so we do the first 5 frames.  More
   // robust alternative would be to actually detect memory writes, but that
   // would be even uglier.)
-  u32 magic = 0xd01f1bad;
-  u32 existing = PowerPC::HostRead_U32(0x80001800);
-  if (existing - magic == 5)
+  u32 gch_gameid = PowerPC::HostRead_U32(Gecko::INSTALLER_BASE_ADDRESS);
+  if (gch_gameid - Gecko::MAGIC_GAMEID == 5)
   {
     return;
   }
-  else if (existing - magic > 5)
+  else if (gch_gameid - Gecko::MAGIC_GAMEID > 5)
   {
-    existing = magic;
+    gch_gameid = Gecko::MAGIC_GAMEID;
   }
-  PowerPC::HostWrite_U32(existing + 1, 0x80001800);
+  PowerPC::HostWrite_U32(gch_gameid + 1, Gecko::INSTALLER_BASE_ADDRESS);
+
   PowerPC::ppcState.iCache.Reset();
 }
 }