Move the code that sets up the exception handlers

exceptions/arm9/source/handlers.h

@@ -7,7 +7,6 @@
 
 #pragma once
 
-void setupStack(u32 mode, void *stack);
 void FIQHandler(void);
 void undefinedInstructionHandler(void);
 void dataAbortHandler(void);

exceptions/arm9/source/handlers.s

@@ -45,16 +45,3 @@ GEN_HANDLER FIQHandler
 GEN_HANDLER undefinedInstructionHandler
 GEN_HANDLER prefetchAbortHandler
 GEN_HANDLER dataAbortHandler
-
-.global setupStack
-.type   setupStack, %function
-setupStack:
-    cmp r0, #0
-    moveq r0, #0xf          @ usr => sys
-    mrs r2, cpsr
-    bic r3, r2, #0xf
-    orr r3, r0              @ processor mode
-    msr cpsr_c, r3          @ change processor mode
-    mov sp, r1
-    msr cpsr_c, r2          @ restore processor mode
-    bx lr

exceptions/arm9/source/mainHandler.c

@@ -1,5 +1,5 @@
 /*
-*   main.c
+*   mainHandler.c
 *       by TuxSH
 *
 *   This is part of Luma3DS, see LICENSE.txt for details
@@ -10,8 +10,6 @@
 #include "handlers.h"
 
 #define FINAL_BUFFER    0x25000000
-#define SP              ((void *)0x02000000)    //We make the (full descending) stack point to the end of ITCM for our exception handlers. 
-                                                //It doesn't matter if we're overwriting stuff, since we're going to reboot.
 
 #define REG_DUMP_SIZE   (4*17)
 #define CODE_DUMP_SIZE  48
@@ -70,22 +68,4 @@ void __attribute__((noreturn)) mainHandler(u32 regs[17], u32 type)
 
     i2cWriteRegister(I2C_DEV_MCU, 0x20, 1 << 2); //Reboot
     while(1);
-}
-
-void main(void)
-{
-    setupStack(1, SP);  //FIQ
-    setupStack(7, SP);  //Abort
-    setupStack(11, SP); //Undefined
-
-    //IRQHandler is at 0x08000000, but we won't handle it for obvious reasons
-    *(vu32 *)0x08000008 = 0xE51FF004;   
-    *(vu32 *)0x0800000C = (u32)FIQHandler;
-    //svcHandler is at 0x08000010, but we won't handle svc either
-    *(vu32 *)0x08000018 = 0xE51FF004;   
-    *(vu32 *)0x0800001C = (u32)undefinedInstructionHandler;
-    *(vu32 *)0x08000020 = 0xE51FF004;   
-    *(vu32 *)0x08000024 = (u32)prefetchAbortHandler;
-    *(vu32 *)0x08000028 = 0xE51FF004;
-    *(vu32 *)0x0800002C = (u32)dataAbortHandler;
 }

exceptions/arm9/source/start.s

@@ -2,4 +2,11 @@
 .align 4
 .global _start
 _start:
-    b main
+    add pc, r0, #(handlers - .) @ Dummy instruction to prevent compiler optimizations
+    
+handlers:
+    .word FIQHandler
+    .word undefinedInstructionHandler
+    .word prefetchAbortHandler
+    .word dataAbortHandler
+    

source/exceptions.c

@@ -12,12 +12,47 @@
 #include "utils.h"
 #include "../build/arm9_exceptions.h"
 
+#define _U __attribute__((unused)) //Silence "unused parameter" warnings
+static void __attribute__((naked)) setupStack(_U u32 mode, _U void* SP)
+{
+    __asm__ volatile(
+            "cmp r0, #0                                         \n"
+            "moveq r0, #0xf          @ usr => sys               \n"
+            "mrs r2, cpsr                                       \n"
+            "bic r3, r2, #0xf                                   \n"
+            "orr r3, r0              @ processor mode           \n"
+            "msr cpsr_c, r3          @ change processor mode    \n"
+            "mov sp, r1                                         \n"
+            "msr cpsr_c, r2          @ restore processor mode   \n"
+            "bx lr                                              \n"
+    );
+}
+#undef _U
+
 void installArm9Handlers(void)
 {
     void *payloadAddress = (void *)0x01FF8000;
-
+    u32 *handlers = (u32 *)payloadAddress + 1;
+    
+    void* SP = (void *)0x02000000; //We make the (full descending) stack point to the end of ITCM for our exception handlers. 
+                                   //It doesn't matter if we're overwriting stuff, since we're going to reboot.
+    
     memcpy(payloadAddress, arm9_exceptions, arm9_exceptions_size);
-    ((void (*)())payloadAddress)();
+    
+    setupStack(1, SP);  //FIQ
+    setupStack(7, SP);  //Abort
+    setupStack(11, SP); //Undefined
+
+    const u32 offsets[] = {0x08, 0x18, 0x20, 0x28};
+    
+    //IRQHandler is at 0x08000000, but we won't handle it for some reasons
+    //svcHandler is at 0x08000010, but we won't handle svc either
+
+    for(u32 i = 0; i < 4; i++)
+    {
+        *(vu32 *)(0x08000000 + offsets[i]) = 0xE51FF004;
+        *(vu32 *)(0x08000000 + offsets[i] + 4) = handlers[i];
+    }
 }
 
 static void hexItoa(u32 n, char *out)