Tested some exceptions; Added a simple panic function

Working exception handlers at the moment:
- und
- swi
- data_abt
Others not tested (yet)

src/dbg.cpp

@@ -32,3 +32,4 @@ extern "C" const char* itoa(uint32_t n) {
     return &string[0];
 }
 
+

src/dbg.s

@@ -1,3 +1,7 @@
+.data
+panic_msg:
+.string "=== PANIC : I'm afraid I have lost my towel"
+
 .text
 
 .extern c_printk
@@ -16,3 +20,14 @@ printk:
 
     pop {pc}
 
+/* TODO: to be implemented in a more useful way */
+.global panic
+panic:
+    cpsid if
+
+    ldr r0, =panic_msg
+    bl printkl
+
+1:
+    wfi
+    b 1b

src/vectab.s

@@ -1,3 +1,6 @@
+/*
+    ARM System Developer's Guide, Chapter 9 Section 1 (y. 2004-2008) (page 323)
+*/
 .data
 und_msg:
 .string "Undefined Instruction"
@@ -16,7 +19,7 @@ fiq_msg:
 .align 4
 .global vectab
 vectab:
-    b _start
+    ldr pc, =panic
     ldr pc, =und_handler
     ldr pc, =swi_handler
     ldr pc, =prefetch_abt_handler
@@ -25,12 +28,11 @@ vectab:
     ldr pc, =irq_handler
     ldr pc, =fiq_handler
 
-// TODO: untested
 und_handler:
     stmfd sp!, {lr}
 
     ldr r0, =und_msg
-    bl printk
+    bl printkl
 
     ldmfd sp!, {pc}^
 
@@ -44,6 +46,7 @@ swi_handler:
 
 // TODO: untested
 prefetch_abt_handler:
+    sub lr, #4
     stmfd sp!, {lr}
 
     ldr r0, =prefetch_abt_msg
@@ -51,13 +54,15 @@ prefetch_abt_handler:
 
     ldmfd sp!, {pc}^
 
-// TODO: untested
 data_abt_handler:
+    sub lr, #8
     stmfd sp!, {lr}
 
     ldr r0, =data_abt_msg
     bl printkl
 
+    b panic
+
     ldmfd sp!, {pc}^
 
 // TODO: untested