Prevent double faults when either PC or SP is invalid

exceptions/arm9/source/handlers.h

@@ -23,6 +23,7 @@
 #pragma once
 #include "types.h"
 
+u32 readMPUConfig(u32 regionSettings[8]);
 void FIQHandler(void);
 void undefinedInstructionHandler(void);
 void dataAbortHandler(void);

exceptions/arm9/source/handlers.s

@@ -62,3 +62,20 @@ GEN_HANDLER FIQHandler
 GEN_HANDLER undefinedInstructionHandler
 GEN_HANDLER prefetchAbortHandler
 GEN_HANDLER dataAbortHandler
+
+.global readMPUConfig
+.type   readMPUConfig, %function
+readMPUConfig:
+    stmfd sp!, {r4-r8}
+    mrc p15,0,r1,c6,c0,0
+    mrc p15,0,r2,c6,c1,0
+    mrc p15,0,r3,c6,c2,0
+    mrc p15,0,r4,c6,c3,0
+    mrc p15,0,r5,c6,c4,0
+    mrc p15,0,r6,c6,c5,0
+    mrc p15,0,r7,c6,c6,0
+    mrc p15,0,r8,c6,c7,0
+    stmia r0, {r1-r8}
+    mrc p15,0,r0,c5,c0,2    @ read data access permission bits
+    ldmfd sp!, {r4-r8}
+    bx lr

exceptions/arm9/source/mainHandler.c

@@ -28,6 +28,29 @@
 #define REG_DUMP_SIZE   (4*17)
 #define CODE_DUMP_SIZE  48
 
+bool cannotAccessAddress(const void *address)
+{
+    u32 regionSettings[8];
+    u32 addr = (u32)address;
+
+    u32 dataAccessPermissions = readMPUConfig(regionSettings);
+    for(u32 i = 0; i < 8; i++)
+    {
+        if((dataAccessPermissions & 0xF) == 0 || (regionSettings[i] & 1) == 0)
+            continue; //no access / region not enabled
+
+        u32 regionAddrBase = regionSettings[i] & ~0xFFF;
+        u32 regionSize = 1 << (((regionSettings[i] >> 1) & 0x1F) + 1);
+
+        if(addr >= regionAddrBase && addr < regionAddrBase + regionSize)
+            return false;
+
+        dataAccessPermissions >>= 4;
+    }
+
+    return true;
+}
+
 void __attribute__((noreturn)) mainHandler(u32 regs[REG_DUMP_SIZE / 4], u32 type)
 {
     ExceptionDumpHeader dumpHeader;
@@ -58,11 +81,13 @@ void __attribute__((noreturn)) mainHandler(u32 regs[REG_DUMP_SIZE / 4], u32 type
     for(u32 i = 0; i < 7; i++) registerDump[8 + i]  = regs[2 + i];
     for(u32 i = 0; i < 8; i++) registerDump[i] = regs[9 + i]; 
 
-    dumpHeader.stackDumpSize = 0x1000 - (registerDump[13] & 0xfff);
+    dumpHeader.stackDumpSize = 0x1000 - (registerDump[13] & 0xFFF);
     dumpHeader.totalSize = sizeof(ExceptionDumpHeader) + dumpHeader.registerDumpSize + dumpHeader.codeDumpSize + dumpHeader.stackDumpSize;
     
     //Dump code
     vu8 *instr = (vu8 *)pc + ((cpsr & 0x20) ? 2 : 4) - dumpHeader.codeDumpSize; //Doesn't work well on 32-bit Thumb instructions, but it isn't much of a problem
+    if(cannotAccessAddress((u8 *)instr) || cannotAccessAddress((u8 *)instr + dumpHeader.codeDumpSize))
+        dumpHeader.codeDumpSize = 0;
     for(u32 i = 0; i < dumpHeader.codeDumpSize; i++)
         codeDump[i] = instr[i];
         
@@ -79,6 +104,8 @@ void __attribute__((noreturn)) mainHandler(u32 regs[REG_DUMP_SIZE / 4], u32 type
         
     //Dump stack in place
     vu32 *sp = (vu32 *)registerDump[13];
+    if(cannotAccessAddress((u8 *)sp))
+        dumpHeader.stackDumpSize = 0;
     for(u32 i = 0; i < dumpHeader.stackDumpSize / 4; i++)
         *final++ = sp[i];
 

exceptions/arm9/source/types.h

@@ -23,6 +23,11 @@
 #pragma once
 
 #include <stdint.h>
+#include <stdbool.h>
+
+#ifndef NULL
+    #define NULL 0
+#endif
 
 //Common data types
 typedef uint8_t u8;