1 files changed, 91 insertions, 0 deletions
diff --git a/lib/kprintf.cc b/lib/kprintf.cc
new file mode 100644
index 0000000..a98de71
--- /dev/null
+++ b/lib/kprintf.cc
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * kprintf.cc — Kernel formatted output
+ *
+ * Uses mpaland/printf's vsnprintf_ as the core formatting engine.
+ *
+ * Architecture:
+ *   vsnprintf_()  ← pure formatting, writes to buffer
+ *       ↓
+ *   kprintf()     ← format + emit via console_write_all()
+ *   kvprintf()    ← va_list variant
+ *   ksnprintf()   ← format into caller's buffer
+ *
+ * Output path:
+ *   Pre-registration:  console_write_all() → early_putc() fallback
+ *   Post-registration: console_write_all() → struct console chain
+ */
+
+#include <lume/kprintf.h>
+#include <lume/console.h>
+#include <lume/atomic.h>
+#include <arch/cpu.h>
+#include "printf.h"
+
+/* ------------------------------------------------------------------ */
+/*  Console spinlock (raw, no scheduler dependency — safe in panic)    */
+/* ------------------------------------------------------------------ */
+
+static lume::atomic<uint32> g_console_lock{0};
+
+static inline void console_lock_acquire()
+{
+    while (g_console_lock.exchange(1, __ATOMIC_ACQUIRE) != 0) {
+        /* spin */
+    }
+}
+
+static inline void console_lock_release()
+{
+    g_console_lock.store(0, __ATOMIC_RELEASE);
+}
+
+/* ------------------------------------------------------------------ */
+/*  _putchar: required by mpaland/printf for printf_() / vprintf_()   */
+/* ------------------------------------------------------------------ */
+
+void _putchar(char character)
+{
+    early_putc(character);
+}
+
+/* ------------------------------------------------------------------ */
+/*  Public API                                                        */
+/* ------------------------------------------------------------------ */
+
+extern "C" int kprintf(const char* fmt, ...)
+{
+    char buf[256];
+    va_list va;
+    va_start(va, fmt);
+    int len = vsnprintf_(buf, sizeof(buf), fmt, va);
+    va_end(va);
+
+    /* Emit to console under lock */
+    console_lock_acquire();
+    console_write_all(buf, len);
+    console_lock_release();
+    return len;
+}
+
+extern "C" int kvprintf(const char* fmt, va_list va)
+{
+    char buf[256];
+    int len = vsnprintf_(buf, sizeof(buf), fmt, va);
+
+    console_lock_acquire();
+    console_write_all(buf, len);
+    console_lock_release();
+    return len;
+}
+
+extern "C" int ksnprintf(char* buf, int count, const char* fmt, ...)
+{
+    va_list va;
+    va_start(va, fmt);
+    int ret = vsnprintf_(buf, (size_t)count, fmt, va);
+    va_end(va);
+    return ret;
+}