Implement first basic interrupt handler

src/vector.S

@@ -0,0 +1,51 @@
+
+.global vector_table
+.extern irq_handler
+
+.macro    ventry    label
+.align    7
+b    \label
+.endm
+
+.section .vector_table, "ax"
+vector_table:
+    ventry .
+    ventry .
+    ventry .
+    ventry .
+
+    ventry .
+    ventry irq_handler     // IRQ(Interrupt Request) 0x280
+
+
+.align 4
+.extern main
+.global el2_to_el1
+el2_to_el1:
+
+    mov x0, #(1 << 31)
+    msr HCR_EL2, x0
+    isb
+
+    // Set SPSR_EL2: return to EL1h (EL1, using SP_EL1)
+    mov x0, #(0b0101)
+    msr SPSR_EL2, x0
+    isb
+
+    // Set return address to ELR_EL2
+    ldr x0, =kernel_main
+    msr ELR_EL2, x0
+    isb
+
+    // Set SP_EL1 to stack base
+    ldr x0, =__stack_end
+    msr SP_EL1, x0
+    isb
+
+    // Set VBAR_EL1 to vector table
+    adr x0, vector_table
+    msr VBAR_EL1, x0
+    isb
+
+    // Return to EL1
+    eret