stos/amd64: cpu: Add Local APIC driver stub

Signed-off-by: Chloe M. <chloe@mensia.org>

paw/stos/arch/amd64/cpu/init.c

@@ -14,6 +14,7 @@
 #include <machine/cpuid.h>
 #include <machine/idt.h>
 #include <machine/msr.h>
+#include <machine/lapic.h>
 #include <stdef.h>
 
 #define DTRACE(Fmt, ...) \
@@ -157,6 +158,12 @@ HalKpcrP2Init(KPCR *Kpcr)
     }
 }
 
+VOID
+HalKpcrP3Init(KPCR *Kpcr)
+{
+    MdLapicInit(Kpcr);
+}
+
 KPCR *
 HalKpcrCurrent(VOID)
 {

paw/stos/arch/amd64/cpu/lapic.c

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: Local APIC driver
+ * Author:      Chloe M.
+ */
+
+#include <machine/lapic.h>
+#include <machine/msr.h>
+#include <machine/cpuid.h>
+#include <ex/trace.h>
+#include <ke/knot.h>
+#include <stdef.h>
+
+/*
+ * Trace only on the bootstrap processor but not on any others
+ * to avoid log spam...
+ */
+#define DTRACE_BSP(Fmt, ...) do {                       \
+        ULONG ApicBase;                                 \
+                                                        \
+        ApicBase = MdRdmsr(IA32_APIC_BASE_MSR);         \
+        if (ISSET(ApicBase, BIT(8))) {                  \
+            TRACE("[ LAPIC ]: " Fmt, ##__VA_ARGS__);    \
+        }                                               \
+    } while (0);
+
+/*
+ * Returns true if the Local APIC unit is supported on the
+ * current processor.
+ */
+static BOOLEAN
+LapicIsSupported(VOID)
+{
+    ULONG Edx, Unused;
+
+    CPUID(1, Unused, Unused, Unused, Edx);
+    return ISSET(Edx, BIT(9)) != 0;
+}
+
+VOID
+MdLapicInit(KPCR *Kpcr)
+{
+    if (Kpcr == NULL) {
+        KeKnot(KNOT_MISC, "failed to initialize lapic driver\n");
+    }
+
+    if (!LapicIsSupported()) {
+        KeKnot(KNOT_MISSING_HARDWARE, "local apic not supported\n");
+    }
+}

paw/stos/head/arch/amd64/lapic.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: Local APIC driver
+ * Author:      Chloe M.
+ */
+
+#ifndef _MACHINE_LAPIC_H_
+#define _MACHINE_LAPIC_H_ 1
+
+#include <stdef.h>
+#include <hal/kpcr.h>
+
+/*
+ * Initialize the Local APIC unit for the current
+ * processor.
+ *
+ * @Kpcr: KPCR of current processor
+ */
+VOID MdLapicInit(KPCR *Kpcr);
+
+#endif  /* !_MACHINE_LAPIC_H_ */

paw/stos/head/hal/kpcr.h

@@ -41,6 +41,13 @@ VOID HalKpcrP1Init(KPCR *Kpcr);
  */
 VOID HalKpcrP2Init(KPCR *Kpcr);
 
+/*
+ * Phase 3 initialization of processor
+ *
+ * @Kpcr: KPCR to initialize
+ */
+VOID HalKpcrP3Init(KPCR *Kpcr);
+
 /*
  * Obtain the KPCR for the current processor, it is never to
  * be of a NULL value.

paw/stos/init/init.c

@@ -86,4 +86,7 @@ KiKernelEntry(VOID)
 
     /* Initialize the board */
     HalBoardInit();
+
+    /* Phase 3 initialization of the bootstrap core */
+    HalKpcrP3Init(&BootstrapCore);
 }