feat: Add initial Supervisor Mode Trap Handler

Implement the initial mechanism for handling traps and exceptions in Supervisor Mode.

Set up the stvec Control and Status Register (CSR) to direct all S-Mode Traps (Interrupts and Exceptions) to a unified assembly entry point.

Implemented assembly code for saving and restoring the Trap Context (register state).

Provides the foundational framework necessary for future Timer Interrupts and System Calls.

1 files changed, 123 insertions, 0 deletions

diff --git a/src/kernel/trap/handler.cc b/src/kernel/trap/handler.cc
new file mode 100644
index 0000000..9cc19d1
--- /dev/null
+++ b/src/kernel/trap/handler.cc
@@ -0,0 +1,123 @@
+#include "kernel/trap.h"
+#include "common/types.h"
+#include "drivers/uart.h"
+
+void panic(const char *s)
+{
+    Drivers::uart_puts("\n\n!!! KERNEL PANIC !!!\n");
+    Drivers::uart_puts(s);
+    Drivers::uart_puts("\nSystem Halted.\n");
+    while (1)
+        ;
+}
+
+namespace Trap
+{
+    void init()
+    {
+        uint64 stvec_val = (uint64)kernelvec;
+        asm volatile("csrw stvec, %0" : : "r"(stvec_val));
+
+        uint64 sstatus;
+        asm volatile("csrr %0, sstatus" : "=r"(sstatus));
+        sstatus &= ~(1L << 1);
+        asm volatile("csrw sstatus, %0" : : "r"(sstatus));
+
+        Drivers::uart_puts("[Trap] Initialized stvec to: ");
+        Drivers::print_hex(stvec_val);
+        Drivers::uart_puts("\n");
+    }
+
+    extern "C" void kerneltrap(struct Trapframe *tf)
+    {
+        uint64 scause, stval, sepc;
+
+        asm volatile("csrr %0, scause" : "=r"(scause));
+        asm volatile("csrr %0, stval" : "=r"(stval));
+        asm volatile("csrr %0, sepc" : "=r"(sepc));
+
+        if (scause & (1L << 63))
+        {
+            uint64 cause_code = scause & 0x7FFFFFFFFFFFFFFFL;
+            switch (cause_code)
+            {
+            case 1:
+                Drivers::uart_puts("[IRQ] Software Interrupt\n");
+                asm volatile("csrc sip, %0" : : "r"(1 << 1));
+                break;
+
+            case 5:
+                Drivers::uart_puts("[IRQ] Timer Interrupt\n");
+
+                break;
+            
+            case 9:
+                Drivers::uart_puts("[IRQ] External Interrupt\n");
+                break;
+
+            default:
+                Drivers::uart_puts("[IRQ] Unknown Interrupt: ");
+                Drivers::print_hex(cause_code);
+                Drivers::uart_puts("\n");
+                break;
+            }
+        }
+        else
+        {
+            switch (scause)
+            {
+            case 8:
+                Drivers::uart_puts("[Syscall] ecall for User Mode\n");
+                tf->epc += 4;
+                break;
+            
+            case 12:
+            case 13:
+            case 15:
+                Drivers::uart_puts("\n--- PAGE FAULT ---\n");
+                Drivers::uart_puts("Cause Code: ");
+                Drivers::print_hex(scause);
+                Drivers::uart_puts("\n");
+                Drivers::uart_puts("Fault Addr (stval): ");
+                Drivers::print_hex(stval);
+                Drivers::uart_puts("\n");
+                Drivers::uart_puts("Instruction (sepc): ");
+                Drivers::print_hex(sepc);
+                Drivers::uart_puts("\n");
+
+                if (stval == 0)
+                {
+                    panic("Null Pointer Dereference!");
+                }
+                else if (stval < 0x80000000)
+                {
+                    panic("Invalid Low Memory Access!");
+                }
+                else
+                {
+                    panic("Segmentation Fault (Unmapped Area)");
+                }
+                break;
+
+            case 2:
+                Drivers::uart_puts("\n--- ILLEGAL INSTRUCTION ---\n");
+                Drivers::uart_puts("Instruction (sepc): ");
+                Drivers::print_hex(sepc);
+                Drivers::uart_puts("\n");
+                panic("CPU encountered an unknown opcode");
+                break;
+
+            default:
+                Drivers::uart_puts("\n--- UNHANDLED EXCEPTION ---\n");
+                Drivers::uart_puts("Cause: ");
+                Drivers::print_hex(scause);
+                Drivers::uart_puts("\n");
+                Drivers::uart_puts("sepc: ");
+                Drivers::print_hex(sepc);
+                Drivers::uart_puts("\n");
+                panic("System Halt");
+                break;
+            }
+        }
+    }
+}
\ No newline at end of file