From eedd2806f9d6c7505130db9fe57d97ce7415e2ba Mon Sep 17 00:00:00 2001
From: Jaklyy <102590697+Jaklyy@users.noreply.github.com>
Date: Mon, 5 Aug 2024 12:37:42 -0400
Subject: [PATCH] Reapply "Improve accuracy of prefetch aborts"

This reverts commit 0dc619d6155b0f6533ff35d13cf5f00add4b1939.
---
 src/ARM.cpp  | 38 ++++++++++++++++++--------------------
 src/CP15.cpp | 29 ++++++++++++++---------------
 2 files changed, 32 insertions(+), 35 deletions(-)

diff --git a/src/ARM.cpp b/src/ARM.cpp
index 6ac387b2..ae55514a 100644
--- a/src/ARM.cpp
+++ b/src/ARM.cpp
@@ -343,12 +343,6 @@ void ARMv5::JumpTo(u32 addr, bool restorecpsr)
         CPSR &= ~0x20;
     }
 
-    if (!(PU_Map[addr>>12] & 0x04))
-    {
-        PrefetchAbort();
-        return;
-    }
-
     NDS.MonitorARM9Jump(addr);
 }
 
@@ -575,15 +569,6 @@ void ARMv5::PrefetchAbort()
     CPSR |= 0x97;
     UpdateMode(oldcpsr, CPSR);
 
-    // this shouldn't happen, but if it does, we're stuck in some nasty endless loop
-    // so better take care of it
-    if (!(PU_Map[ExceptionBase>>12] & 0x04))
-    {
-        Log(LogLevel::Error, "!!!!! EXCEPTION REGION NOT EXECUTABLE. THIS IS VERY BAD!!\n");
-        NDS.Stop(Platform::StopReason::BadExceptionRegion);
-        return;
-    }
-
     R_ABT[2] = oldcpsr;
     R[14] = R[15] + (oldcpsr & 0x20 ? 2 : 0);
     JumpTo(ExceptionBase + 0x0C);
@@ -685,10 +670,18 @@ void ARMv5::Execute()
                 NextInstr[0] = NextInstr[1];
                 if (R[15] & 0x2) { NextInstr[1] >>= 16; CodeCycles = 0; }
                 else             NextInstr[1] = CodeRead32(R[15], false);
-
+                
+                // handle aborted instructions
+                if (!(PU_Map[(R[15]-4)>>12] & 0x04)) [[unlikely]]
+                {
+                    PrefetchAbort();
+                }
                 // actually execute
-                u32 icode = (CurInstr >> 6) & 0x3FF;
-                ARMInterpreter::THUMBInstrTable[icode](this);
+                else [[likely]]
+                {
+                    u32 icode = (CurInstr >> 6) & 0x3FF;
+                    ARMInterpreter::THUMBInstrTable[icode](this);
+                }
             }
             else
             {
@@ -700,9 +693,14 @@ void ARMv5::Execute()
                 CurInstr = NextInstr[0];
                 NextInstr[0] = NextInstr[1];
                 NextInstr[1] = CodeRead32(R[15], false);
-
+                
+                // handle aborted instructions
+                if (!(PU_Map[(R[15]-8)>>12] & 0x04)) [[unlikely]] // todo: check for bkpt instruction?
+                {
+                    PrefetchAbort();
+                }
                 // actually execute
-                if (CheckCondition(CurInstr >> 28))
+                else if (CheckCondition(CurInstr >> 28)) [[likely]]
                 {
                     u32 icode = ((CurInstr >> 4) & 0xF) | ((CurInstr >> 16) & 0xFF0);
                     ARMInterpreter::ARMInstrTable[icode](this);
diff --git a/src/CP15.cpp b/src/CP15.cpp
index bf1d2edc..6fcaff93 100644
--- a/src/CP15.cpp
+++ b/src/CP15.cpp
@@ -773,14 +773,13 @@ u32 ARMv5::CP15Read(u32 id) const
 
 u32 ARMv5::CodeRead32(u32 addr, bool branch)
 {
-    /*if (branch || (!(addr & 0xFFF)))
+    // prefetch abort
+    // the actual exception is not raised until the aborted instruction is executed
+    if (!(PU_Map[addr>>12] & 0x04)) [[unlikely]]
     {
-        if (!(PU_Map[addr>>12] & 0x04))
-        {
-            PrefetchAbort();
-            return 0;
-        }
-    }*/
+        CodeCycles = 1;
+        return 0;
+    }
 
     if (addr < ITCMSize)
     {
@@ -807,7 +806,7 @@ u32 ARMv5::CodeRead32(u32 addr, bool branch)
 
 bool ARMv5::DataRead8(u32 addr, u32* val)
 {
-    if (!(PU_Map[addr>>12] & 0x01))
+    if (!(PU_Map[addr>>12] & 0x01)) [[unlikely]]
     {
         DataAbort();
         return false;
@@ -833,7 +832,7 @@ bool ARMv5::DataRead8(u32 addr, u32* val)
 
 bool ARMv5::DataRead16(u32 addr, u32* val)
 {
-    if (!(PU_Map[addr>>12] & 0x01))
+    if (!(PU_Map[addr>>12] & 0x01)) [[unlikely]]
     {
         DataAbort();
         return false;
@@ -861,7 +860,7 @@ bool ARMv5::DataRead16(u32 addr, u32* val)
 
 bool ARMv5::DataRead32(u32 addr, u32* val)
 {
-    if (!(PU_Map[addr>>12] & 0x01))
+    if (!(PU_Map[addr>>12] & 0x01)) [[unlikely]]
     {
         DataAbort();
         return false;
@@ -889,7 +888,7 @@ bool ARMv5::DataRead32(u32 addr, u32* val)
 
 bool ARMv5::DataRead32S(u32 addr, u32* val)
 {
-    if (!(PU_Map[addr>>12] & 0x01))
+    if (!(PU_Map[addr>>12] & 0x01)) [[unlikely]]
     {
         DataAbort();
         return false;
@@ -917,7 +916,7 @@ bool ARMv5::DataRead32S(u32 addr, u32* val)
 
 bool ARMv5::DataWrite8(u32 addr, u8 val)
 {
-    if (!(PU_Map[addr>>12] & 0x02))
+    if (!(PU_Map[addr>>12] & 0x02)) [[unlikely]]
     {
         DataAbort();
         return false;
@@ -944,7 +943,7 @@ bool ARMv5::DataWrite8(u32 addr, u8 val)
 
 bool ARMv5::DataWrite16(u32 addr, u16 val)
 {
-    if (!(PU_Map[addr>>12] & 0x02))
+    if (!(PU_Map[addr>>12] & 0x02)) [[unlikely]]
     {
         DataAbort();
         return false;
@@ -973,7 +972,7 @@ bool ARMv5::DataWrite16(u32 addr, u16 val)
 
 bool ARMv5::DataWrite32(u32 addr, u32 val)
 {
-    if (!(PU_Map[addr>>12] & 0x02))
+    if (!(PU_Map[addr>>12] & 0x02)) [[unlikely]]
     {
         DataAbort();
         return false;
@@ -1002,7 +1001,7 @@ bool ARMv5::DataWrite32(u32 addr, u32 val)
 
 bool ARMv5::DataWrite32S(u32 addr, u32 val, bool dataabort)
 {
-    if (!(PU_Map[addr>>12] & 0x02))
+    if (!(PU_Map[addr>>12] & 0x02)) [[unlikely]]
     {
         if (!dataabort) DataAbort();
         return false;