From e5c4139e498220a2d487e1dbb8ece0319dfedb35 Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Mon, 24 Aug 2026 19:45:21 +0200
Subject: [PATCH] feat(cpu): install IDT with exception and syscall gate
 handling

---
 include/idt.h |  6 +++++
 include/isr.h | 16 +++++++++++
 src/idt.c     | 48 +++++++++++++++++++++++++++++++++
 src/isr.c     | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 145 insertions(+)
 create mode 100644 include/idt.h
 create mode 100644 include/isr.h
 create mode 100644 src/idt.c
 create mode 100644 src/isr.c

diff --git a/include/idt.h b/include/idt.h
new file mode 100644
index 0000000..a41026d
--- /dev/null
+++ b/include/idt.h
@@ -0,0 +1,6 @@
+#ifndef FROSTBYTE_IDT_H
+#define FROSTBYTE_IDT_H
+
+void idtInit(void);
+
+#endif
diff --git a/include/isr.h b/include/isr.h
new file mode 100644
index 0000000..026516f
--- /dev/null
+++ b/include/isr.h
@@ -0,0 +1,16 @@
+#ifndef FROSTBYTE_ISR_H
+#define FROSTBYTE_ISR_H
+
+#include "types.h"
+
+typedef struct Registers {
+    uint64 r15, r14, r13, r12, r11, r10, r9, r8;
+    uint64 rbp, rdi, rsi, rdx, rcx, rbx, rax;
+    uint64 intNo, errCode;
+    uint64 rip, cs, rflags, rsp, ss;
+} __attribute__((packed)) Registers;
+
+uint64 isrDispatch(Registers* regs);
+uint64 syscallDispatch(Registers* regs);
+
+#endif
diff --git a/src/idt.c b/src/idt.c
new file mode 100644
index 0000000..8267c68
--- /dev/null
+++ b/src/idt.c
@@ -0,0 +1,48 @@
+#include "idt.h"
+#include "types.h"
+
+typedef struct IdtEntry {
+    uint16 offsetLow;
+    uint16 selector;
+    uint8 ist;
+    uint8 typeAttr;
+    uint16 offsetMid;
+    uint32 offsetHigh;
+    uint32 reserved;
+} __attribute__((packed)) IdtEntry;
+
+typedef struct IdtPointer {
+    uint16 limit;
+    uint64 base;
+} __attribute__((packed)) IdtPointer;
+
+static IdtEntry idtEntries[256];
+static IdtPointer idtPointer;
+
+extern void* isrStubTable[];
+extern void isrStub128(void);
+
+static void setGate(int vector, void* handler, uint8 typeAttr)
+{
+    uint64 address = (uint64)handler;
+    idtEntries[vector].offsetLow = (uint16)(address & 0xFFFF);
+    idtEntries[vector].selector = 0x08;
+    idtEntries[vector].ist = 0;
+    idtEntries[vector].typeAttr = typeAttr;
+    idtEntries[vector].offsetMid = (uint16)((address >> 16) & 0xFFFF);
+    idtEntries[vector].offsetHigh = (uint32)((address >> 32) & 0xFFFFFFFF);
+    idtEntries[vector].reserved = 0;
+}
+
+void idtInit(void)
+{
+    for (int vector = 0; vector < 48; vector++)
+        setGate(vector, isrStubTable[vector], 0x8E);
+
+    setGate(0x80, (void*)isrStub128, 0xEE);
+
+    idtPointer.limit = (uint16)(sizeof(idtEntries) - 1);
+    idtPointer.base = (uint64)&idtEntries;
+
+    __asm__ volatile("lidt %0" : : "m"(idtPointer));
+}
diff --git a/src/isr.c b/src/isr.c
new file mode 100644
index 0000000..9f83d18
--- /dev/null
+++ b/src/isr.c
@@ -0,0 +1,75 @@
+#include "isr.h"
+#include "console.h"
+#include "pic.h"
+#include "pit.h"
+#include "keyboard.h"
+#include "sched.h"
+#include "ports.h"
+
+static const char* exceptionNames[32] = {
+    "divide by zero",
+    "debug",
+    "non maskable interrupt",
+    "breakpoint",
+    "overflow",
+    "bound range exceeded",
+    "invalid opcode",
+    "device not available",
+    "double fault",
+    "coprocessor segment overrun",
+    "invalid tss",
+    "segment not present",
+    "stack segment fault",
+    "general protection fault",
+    "page fault",
+    "reserved",
+    "x87 floating point",
+    "alignment check",
+    "machine check",
+    "simd floating point",
+    "virtualization",
+    "control protection",
+    "reserved", "reserved", "reserved", "reserved",
+    "reserved", "reserved", "reserved", "reserved",
+    "hypervisor injection", "vmm communication"
+};
+
+static void panicOnException(Registers* regs)
+{
+    uint64 faultAddress = 0;
+    if (regs->intNo == 14)
+        __asm__ volatile("mov %%cr2, %0" : "=r"(faultAddress));
+
+    kprintf("\n[PANIC] exception %lu (%s)\n", regs->intNo, exceptionNames[regs->intNo]);
+    kprintf("  errCode=%lx rip=%lx cs=%lx rflags=%lx\n",
+            regs->errCode, regs->rip, regs->cs, regs->rflags);
+    if (regs->intNo == 14)
+        kprintf("  cr2=%lx (faulting address)\n", faultAddress);
+    kprintf("  rax=%lx rbx=%lx rcx=%lx rdx=%lx\n", regs->rax, regs->rbx, regs->rcx, regs->rdx);
+    kprintf("  system halted\n");
+
+    for (;;)
+        __asm__ volatile("cli; hlt");
+}
+
+uint64 isrDispatch(Registers* regs)
+{
+    if (regs->intNo < 32)
+        panicOnException(regs);
+
+    if (regs->intNo == 128)
+        return syscallDispatch(regs);
+
+    uint8 irq = (uint8)(regs->intNo - 32);
+    uint64 nextRsp = (uint64)regs;
+
+    if (irq == 0) {
+        pitTick();
+        nextRsp = schedule((uint64)regs);
+    } else if (irq == 1) {
+        keyboardHandler();
+    }
+
+    picSendEoi(irq);
+    return nextRsp;
+}