m1x/x86_64: Add interrupt descriptor table groundwork

Signed-off-by: Ian Moffett <ian@mirocom.org>

src/m1x/arch/x86_64/cpu/cpu_idt.c

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2026, Mirocom Laboratories
+ * Provided under the BSD-3 clause
+ */
+
+#include <machine/idt.h>
+#include <machine/gdt.h>
+
+__align(8) static struct idt_gate idt[256];
+static struct idtr idtr = {
+    .limit = sizeof(idt) - 1,
+    .base = (uintptr_t)&idt[0]
+};
+
+void
+md_idt_gate_set(uint8_t vector, uintptr_t isr, uint8_t ist, uint8_t type)
+{
+    struct idt_gate *gate;
+
+    gate = &idt[vector];
+    gate->offset_low   = (isr & 0xFFFF);
+    gate->offset_mid   = (isr >> 16) & 0xFFFF;
+    gate->offset_high  = (isr >> 32) & 0xFFFFFFFF;
+    gate->p = 1;
+    gate->dpl = (type == IDT_USER_GATE) ? 3 : 0;
+    gate->zero = 0;
+    gate->zero1 = 0;
+    gate->reserved = 0;
+    gate->type = type;
+    gate->ist = ist;
+    gate->segment_sel = GDT_KCODE;
+}
+
+void
+md_idt_load(void)
+{
+    __asmv("lidt %0" :: "m" (idtr) : "memory");
+}

src/m1x/include/arch/x86_64/gdt.h

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2026, Mirocom Laboratories
+ * Provided under the BSD-3 clause
+ */
+
+#ifndef _MACHINE_GDT_H_
+#define _MACHINE_GDT_H_ 1
+
+/* Kernel code/data */
+#define GDT_KCODE  0x08
+#define GDT_KDATA  0x10
+
+/* User code/data */
+#define GDT_UCODE  0x18
+#define GDT_UDATA  0x20
+
+/* Task state segment */
+#define GDT_TSS    0x28
+#define GDT_TSS_INDEX 0x05
+
+#endif  /* !_MACHINE_GDT_H_ */

src/m1x/include/arch/x86_64/idt.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2026, Mirocom Laboratories
+ * Provided under the BSD-3 clause
+ */
+
+#ifndef _MACHINE_IDT_H_
+#define _MACHINE_IDT_H_ 1
+
+#include <sys/types.h>
+#include <sys/cdefs.h>
+
+#define IDT_INT_GATE    0x8E
+#define IDT_TRAP_GATE   0x8F
+#define IDT_USER_GATE   0xEE
+
+/*
+ * Represents an interrupt descriptor table gate
+ * entry
+ */
+struct idt_gate {
+    uint16_t offset_low;
+    uint16_t segment_sel;
+    uint8_t ist   : 3;
+    uint8_t zero  : 5;
+    uint8_t type  : 4;
+    uint8_t zero1 : 1;
+    uint8_t dpl   : 2;
+    uint8_t p     : 1;
+    uint16_t offset_mid;
+    uint32_t offset_high;
+    uint32_t reserved;
+};
+
+/*
+ * References an interrupt descriptor table
+ */
+struct __packed idtr {
+    uint16_t limit;
+    uintptr_t base;
+};
+
+/*
+ * Set an entry in the interrupt descriptor table
+ *
+ * @vector:  Interrupt vector to set
+ * @isr:     Interrupt service routine base
+ * @ist:     Interrupt stack table
+ * @type:    Interrupt gate type
+ */
+void md_idt_gate_set(uint8_t vector, uintptr_t isr, uint8_t ist, uint8_t type);
+
+/*
+ * Load the interrupt descriptor table register
+ */
+void md_idt_load(void);
+
+#endif  /* !_MACHINE_IDT_H_ */