install kernel GDT

Author: tas0dev

src/boot/config.inc

@@ -1,5 +1,5 @@
 KERNEL_OFFSET EQU 0x10000       ; カーネルをロードするアドレス
-SECTOR_COUNT  EQU 29            ; 読み込むセクタの数
+SECTOR_COUNT  EQU 30            ; 読み込むセクタの数
 START_SECTOR  EQU 2             ; 開始するセクタ番号
 CYLINDER_NUM  EQU 0             ; シリンダ番号
 HEAD_NUM      EQU 0             ; ヘッド番号

src/include/config.h

@@ -25,6 +25,12 @@
  */
 typedef unsigned char uint8_t;
 
+/**
+ * @typedef uint16_t
+ * @brief 16ビット符号なし整数型
+ */
+typedef unsigned short uint16_t;
+
 /**
  * @typedef uint32_t
  * @brief 32bit符号なし整数型

src/include/mem/segment.h

@@ -0,0 +1,6 @@
+#ifndef _MEM_SEGMENT_H
+#define _MEM_SEGMENT_H
+
+void gdt_install();
+
+#endif /* _MEM_SEGMENT_H */

src/include/tests/define.h

@@ -13,6 +13,8 @@
 #define INTERRUPT_VECTOR_TEST
 // 割り込みハンドラでメモリのテスト
 #define ALLOC_IRQ_TEST
+// GDT（セグメント）再構築テスト
+#define GDT_TEST
 
 /* -------- 宣言 -------- */
 #ifdef MEM_TEST
@@ -31,6 +33,10 @@ void interrupt_vector_test();
 void alloc_irq_test();
 #endif /* ALLOC_IRQ_TEST */
 
+#ifdef GDT_TEST
+void gdt_test();
+#endif /* GDT_TEST */
+
 #endif /* TEST_TRUE */
 
 #endif /* _TESTS_CONFIG_H */

src/kernel/main.c

@@ -6,6 +6,7 @@
 #include <interrupt/idt.h>
 #include <mem/map.h>
 #include <mem/manager.h>
+#include <mem/segment.h>
 
 #include <tests/define.h>
 #include <tests/run.h>
@@ -18,6 +19,7 @@ void kloop();
  */
 void kmain() {
         console_init();
+        gdt_install();
 
         printk("Welcome to Litecore kernel!\n");
         printk("    Version: %s\n", VERSION);

src/kernel/mem/segment.c

@@ -0,0 +1,68 @@
+#include <config.h>
+#include <stdint.h>
+
+/* GDTエントリ構造体 */
+struct gdt_entry {
+        uint16_t limit_low;
+        uint16_t base_low;
+        uint8_t base_middle;
+        uint8_t access;
+        uint8_t granularity;
+        uint8_t base_high;
+} __attribute__((packed));
+
+struct gdt_ptr {
+        uint16_t limit;
+        uint32_t base;
+} __attribute__((packed));
+
+/* ここではNULL, kernel code, kernel data, user code, user dataの5つ */
+static struct gdt_entry gdt_entries[5];
+static struct gdt_ptr gp;
+
+static void gdt_set_gate(int num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran) {
+        gdt_entries[num].base_low = (base & 0xFFFF);
+        gdt_entries[num].base_middle = (base >> 16) & 0xFF;
+        gdt_entries[num].base_high = (base >> 24) & 0xFF;
+
+        gdt_entries[num].limit_low = (limit & 0xFFFF);
+        gdt_entries[num].granularity = (limit >> 16) & 0x0F;
+
+        gdt_entries[num].granularity |= (gran & 0xF0);
+        gdt_entries[num].access = access;
+}
+
+/**
+ * @fn gdt_install
+ * @brief カーネル側でGDTを再構築してロードする
+ */
+void gdt_install() {
+        gdt_set_gate(0, 0, 0, 0, 0);
+
+        /* Kernel code segment: base=0, limit=0xFFFFF, access=0x9A, gran=0xCF */
+        gdt_set_gate(1, 0x0, 0xFFFFF, 0x9A, 0xCF);
+        /* Kernel data segment */
+        gdt_set_gate(2, 0x0, 0xFFFFF, 0x92, 0xCF);
+        /* User code (ring3) */
+        gdt_set_gate(3, 0x0, 0xFFFFF, 0xFA, 0xCF);
+        /* User data (ring3) */
+        gdt_set_gate(4, 0x0, 0xFFFFF, 0xF2, 0xCF);
+
+        gp.limit = (sizeof(struct gdt_entry) * 5) - 1;
+        gp.base = (uint32_t)&gdt_entries;
+
+        asm volatile(
+                "lgdt (%0)\n"
+                "pushl $0x08\n"
+                "pushl $1f\n"
+                "lret\n"
+                "1:\n"
+                "mov $0x10, %%ax\n"
+                "mov %%ax, %%ds\n"
+                "mov %%ax, %%es\n"
+                "mov %%ax, %%fs\n"
+                "mov %%ax, %%gs\n"
+                "mov %%ax, %%ss\n"
+                :: "r"(&gp) : "eax", "memory"
+        );
+}

src/kernel/tests/gdt_test.c

@@ -0,0 +1,34 @@
+#include <tests/define.h>
+
+#ifdef GDT_TEST
+
+#include <config.h>
+#include <console.h>
+
+static inline uint16_t read_cs(void) {
+    uint16_t sel;
+    asm volatile ("mov %%cs, %0" : "=r" (sel));
+    return sel;
+}
+
+static inline uint16_t read_ds(void) {
+    uint16_t sel;
+    asm volatile ("mov %%ds, %0" : "=r" (sel));
+    return sel;
+}
+
+void gdt_test() {
+    uint16_t cs = read_cs();
+    uint16_t ds = read_ds();
+    printk("> GDT TEST\n");
+    printk("CS = 0x%x\n", (unsigned)cs);
+    printk("DS = 0x%x\n", (unsigned)ds);
+    /* check expected values: kernel code=0x08, data=0x10 */
+    if (cs == 0x08 && ds == 0x10) {
+        printk("GDT test: OK\n");
+    } else {
+        printk("GDT test: FAILED (cs=0x%x ds=0x%x)\n", (unsigned)cs, (unsigned)ds);
+    }
+}
+
+#endif /* GDT_TEST */

src/kernel/tests/run.c

@@ -28,4 +28,10 @@ void run_test() {
         printk("> ALOOC IRQ TEST\n");
         alloc_irq_test();
         #endif
+
+        new_line();
+
+        #ifdef GDT_TEST
+        gdt_test();
+        #endif
 }