Merge pull request #13996 from SuperSamus/jit64-dynamic-known-jmp-len

Jit64: Dynamic length of regular jump instruction (for known addresses)

2 files changed, 21 insertions, 15 deletions

diff --git a/Source/Core/Common/x64Emitter.cpp b/Source/Core/Common/x64Emitter.cpp
index 3db669e9b2..46b117a87f 100644
--- a/Source/Core/Common/x64Emitter.cpp
+++ b/Source/Core/Common/x64Emitter.cpp
@@ -412,27 +412,31 @@ void XEmitter::Rex(int w, int r, int x, int b)
     Write8(rx);
 }
 
-void XEmitter::JMP(const u8* addr, const Jump jump)
+void XEmitter::JMP(const u8* addr, bool force_near_padding)
 {
   u64 fn = (u64)addr;
-  if (jump == Jump::Short)
-  {
-    s64 distance = (s64)(fn - ((u64)code + 2));
-    ASSERT_MSG(DYNA_REC, distance >= -0x80 && distance < 0x80,
-               "Jump::Short target too far away ({}), needs Jump::Near", distance);
-    // 8 bits will do
-    Write8(0xEB);
-    Write8((u8)(s8)distance);
-  }
-  else
+  s64 distance = (s64)(fn - ((u64)code + SHORT_JMP_LEN));
+  if (distance < -0x80 || distance >= 0x80)
   {
-    s64 distance = (s64)(fn - ((u64)code + 5));
-
+    distance = (s64)(fn - ((u64)code + NEAR_JMP_LEN));
     ASSERT_MSG(DYNA_REC, distance >= -0x80000000LL && distance < 0x80000000LL,
-               "Jump::Near target too far away ({}), needs indirect register", distance);
+               "Jump target too far away ({}), needs indirect register", distance);
     Write8(0xE9);
     Write32((u32)(s32)distance);
   }
+  else
+  {
+    Write8(0xEB);
+    Write8((u8)(s8)distance);
+    if (force_near_padding)
+    {
+      for (int i = 0; i < NEAR_JMP_LEN - SHORT_JMP_LEN; i++)
+      {
+        // INT3 is more efficient than NOP if never executed, as it stops CPU speculation.
+        INT3();
+      }
+    }
+  }
 }
 
 void XEmitter::JMPptr(const OpArg& arg2)
diff --git a/Source/Core/Common/x64Emitter.h b/Source/Core/Common/x64Emitter.h
index 3c8a411159..71dcea30f9 100644
--- a/Source/Core/Common/x64Emitter.h
+++ b/Source/Core/Common/x64Emitter.h
@@ -444,6 +444,8 @@ public:
     Short,
     Near,
   };
+  static const int SHORT_JMP_LEN = 2;
+  static const int NEAR_JMP_LEN = 5;
 
   // Flow control
   void RET();
@@ -451,7 +453,7 @@ public:
   void UD2();
   [[nodiscard]] FixupBranch J(Jump jump = Jump::Short);
 
-  void JMP(const u8* addr, Jump jump = Jump::Short);
+  void JMP(const u8* addr, bool force_near_padding = false);
   void JMPptr(const OpArg& arg);
   void JMPself();  // infinite loop!
 #ifdef CALL