From 9479f3d3641d67ac7bef38879135933e63ae78b4 Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Wed, 25 Mar 2026 22:52:58 +0100
Subject: [PATCH] Implement APIC presence check and panic if unsupported

---
 xtoskrnl/hl/x86/pic.cc      | 43 +++++++++++++++++++++++++++++++++++++
 xtoskrnl/includes/hl/pic.hh |  1 +
 2 files changed, 44 insertions(+)

diff --git a/xtoskrnl/hl/x86/pic.cc b/xtoskrnl/hl/x86/pic.cc
index 2d31e2ba..8fefc6c2 100644
--- a/xtoskrnl/hl/x86/pic.cc
+++ b/xtoskrnl/hl/x86/pic.cc
@@ -9,6 +9,41 @@
 #include <xtos.hh>
 
 
+/**
+ * Checks whether the APIC is supported by the processor.
+ *
+ * @return This routine returns TRUE if APIC is supported, or FALSE otherwise.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+BOOLEAN
+HL::Pic::CheckApicSupport(VOID)
+{
+    CPUID_REGISTERS CpuRegisters;
+
+    /* Prepare CPUID registers */
+    CpuRegisters.Leaf = CPUID_GET_STANDARD1_FEATURES;
+    CpuRegisters.SubLeaf = 0;
+    CpuRegisters.Eax = 0;
+    CpuRegisters.Ebx = 0;
+    CpuRegisters.Ecx = 0;
+    CpuRegisters.Edx = 0;
+
+    /* Get CPUID */
+    AR::CpuFunc::CpuId(&CpuRegisters);
+
+    /* Check APIC status from the CPUID results */
+    if(!(CpuRegisters.Edx & CPUID_FEATURES_EDX_APIC))
+    {
+        /* APIC is not supported */
+        return FALSE;
+    }
+
+    /* APIC is supported */
+    return TRUE;
+}
+
 /**
  * Checks whether the x2APIC extension is supported by the processor.
  *
@@ -124,6 +159,14 @@ HL::Pic::InitializeApic(VOID)
     APIC_LVT_REGISTER LvtRegister;
     ULONG CpuNumber;
 
+    /* Check APIC support */
+    if(!CheckApicSupport())
+    {
+        /* APIC is not supported, raise kernel panic */
+        DebugPrint(L"FATAL ERROR: Local APIC not present.\n");
+        KE::Crash::Panic(0x5D, CPUID_GET_STANDARD1_FEATURES, 0x0, 0x0, CPUID_FEATURES_EDX_APIC);
+    }
+
     /* Determine APIC mode (xAPIC compatibility or x2APIC) */
     if(CheckX2ApicSupport())
     {
diff --git a/xtoskrnl/includes/hl/pic.hh b/xtoskrnl/includes/hl/pic.hh
index 85b8fcae..c90b0980 100644
--- a/xtoskrnl/includes/hl/pic.hh
+++ b/xtoskrnl/includes/hl/pic.hh
@@ -32,6 +32,7 @@ namespace HL
                                                      IN ULONGLONG Value);
 
         private:
+            STATIC XTAPI BOOLEAN CheckApicSupport(VOID);
             STATIC XTAPI BOOLEAN CheckX2ApicSupport(VOID);
             STATIC XTCDECL VOID HandleApicSpuriousService(VOID);
             STATIC XTCDECL VOID HandlePicSpuriousService(VOID);