Boot to C in 64-bit long mode

kernel/arch/x86_64/console.c

@@ -0,0 +1,76 @@
+/* Nadir console: VGA text-mode driver (see console.h). */
+
+#include <stdint.h>
+
+#include "console.h"
+
+#define VGA_WIDTH 80
+#define VGA_HEIGHT 25
+#define VGA_ADDR 0xB8000
+#define COLOR_DEFAULT 0x0FU /* white on black */
+
+/* Cursor position. Lives in BSS, zeroed by stage 2 before kmain runs. */
+static uint8_t cursor_row;
+static uint8_t cursor_col;
+
+static volatile uint16_t *const vga = (uint16_t *)VGA_ADDR;
+
+static void scroll(void)
+{
+    for (uint8_t row = 1; row < VGA_HEIGHT; row++) {
+        for (uint8_t col = 0; col < VGA_WIDTH; col++) {
+            vga[(row - 1) * VGA_WIDTH + col] = vga[row * VGA_WIDTH + col];
+        }
+    }
+    for (uint8_t col = 0; col < VGA_WIDTH; col++) {
+        vga[(VGA_HEIGHT - 1) * VGA_WIDTH + col] =
+            (uint16_t)((COLOR_DEFAULT << 8) | ' ');
+    }
+}
+
+void console_clear(void)
+{
+    for (uint16_t i = 0; i < VGA_WIDTH * VGA_HEIGHT; i++) {
+        vga[i] = (uint16_t)((COLOR_DEFAULT << 8) | ' ');
+    }
+    cursor_row = 0;
+    cursor_col = 0;
+}
+
+void console_putchar(char c)
+{
+    if (c == '\n') {
+        cursor_row++;
+        cursor_col = 0;
+    } else {
+        vga[cursor_row * VGA_WIDTH + cursor_col] =
+            (uint16_t)((COLOR_DEFAULT << 8) | c);
+        cursor_col++;
+        if (cursor_col >= VGA_WIDTH) {
+            cursor_col = 0;
+            cursor_row++;
+        }
+    }
+    if (cursor_row >= VGA_HEIGHT) {
+        scroll();
+        cursor_row = VGA_HEIGHT - 1;
+    }
+}
+
+void console_puts(const char *s)
+{
+    while (*s != '\0') {
+        console_putchar(*s);
+        s++;
+    }
+}
+
+void console_puthex64(uint64_t value)
+{
+    static const char digits[] = "0123456789ABCDEF";
+
+    console_puts("0x");
+    for (int shift = 60; shift >= 0; shift -= 4) {
+        console_putchar(digits[(value >> shift) & 0xFU]);
+    }
+}