Kernel: Add serial_debug cmdline parameter

serial_debug will output all the kprintf and dbgprintf data to COM1 at
8-N-1 57600 baud. this is particularly useful for debugging the boot
process on live hardware.

Note: it must be the first parameter in the boot cmdline.

Kernel/grub.cfg

@@ -1,6 +1,11 @@
-timeout=0
+timeout=1
 
-menuentry 'Serenity' {
+menuentry 'Serenity (normal)' {
   root=hd0,1
   multiboot /boot/kernel root=/dev/hda1
 }
+
+menuentry 'Serenity (with serial debug)' {
+	root=hd0,1
+  multiboot /boot/kernel serial_debug root=/dev/hda1
+}

Kernel/init.cpp

@@ -4,6 +4,7 @@
 #include "RTC.h"
 #include "Scheduler.h"
 #include "kmalloc.h"
+#include "kstdio.h"
 #include <AK/Types.h>
 #include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/Arch/i386/PIC.h>
@@ -155,6 +156,25 @@ multiboot_info_t* multiboot_info_ptr;
 
 extern "C" [[noreturn]] void init()
 {
+    // this is only used one time, directly below here. we can't use this part
+    // of libc at this point in the boot process, or we'd just pull strstr in
+    // from <string.h>.
+    auto bad_prefix_check = [](const char *str, const char *search) -> bool {
+        while (*search)
+            if (*search++ != *str++)
+                return false;
+
+        return true;
+    };
+
+    // serial_debug will output all the kprintf and dbgprintf data to COM1 at
+    // 8-N-1 57600 baud. this is particularly useful for debugging the boot
+    // process on live hardware.
+    //
+    // note: it must be the first option in the boot cmdline.
+    if (multiboot_info_ptr->cmdline && bad_prefix_check(reinterpret_cast<const char*>(multiboot_info_ptr->cmdline), "serial_debug"))
+        set_serial_debug(true);
+
     sse_init();
 
     kmalloc_init();
@@ -177,7 +197,8 @@ extern "C" [[noreturn]] void init()
     ps2mouse = new PS2MouseDevice;
     sb16 = new SB16;
     dev_null = new NullDevice;
-    ttyS0 = new SerialDevice(SERIAL_COM1_ADDR, 64);
+    if (!get_serial_debug())
+        ttyS0 = new SerialDevice(SERIAL_COM1_ADDR, 64);
     ttyS1 = new SerialDevice(SERIAL_COM2_ADDR, 65);
     ttyS2 = new SerialDevice(SERIAL_COM3_ADDR, 66);
     ttyS3 = new SerialDevice(SERIAL_COM4_ADDR, 67);

Kernel/kprintf.cpp

@@ -6,6 +6,18 @@
 #include <Kernel/kstdio.h>
 #include <LibC/stdarg.h>
 
+static bool serial_debug;
+
+void set_serial_debug(bool on_or_off)
+{
+    serial_debug = on_or_off;
+}
+
+int get_serial_debug()
+{
+    return serial_debug;
+}
+
 static void color_on()
 {
     IO::out8(0xe9, 0x1b);
@@ -22,8 +34,42 @@ static void color_off()
     IO::out8(0xe9, '0');
     IO::out8(0xe9, 'm');
 }
+
+static void serial_putch(char ch)
+{
+    static bool serial_ready = false;
+    static bool was_cr = false;
+
+    if (!serial_ready) {
+        IO::out8(0x3F8 + 1, 0x00);
+        IO::out8(0x3F8 + 3, 0x80);
+        IO::out8(0x3F8 + 0, 0x02);
+        IO::out8(0x3F8 + 1, 0x00);
+        IO::out8(0x3F8 + 3, 0x03);
+        IO::out8(0x3F8 + 2, 0xC7);
+        IO::out8(0x3F8 + 4, 0x0B);
+
+        serial_ready = true;
+    }
+
+    while ((IO::in8(0x3F8 + 5) & 0x20) == 0)
+        ;
+
+    if (ch == '\n' && !was_cr)
+        IO::out8(0x3F8, '\r');
+
+    IO::out8(0x3F8, ch);
+
+    if (ch == '\r')
+        was_cr = true;
+    else
+        was_cr = false;
+}
+
 static void console_putch(char*&, char ch)
 {
+    if (serial_debug)
+        serial_putch(ch);
     if (!current) {
         IO::out8(0xe9, ch);
         return;
@@ -57,16 +103,23 @@ int ksprintf(char* buffer, const char* fmt, ...)
     return ret;
 }
 
-extern "C" int dbgputstr(const char* characters, int length)
+static void debugger_out(char ch)
 {
-    for (int i = 0; i < length; ++i)
-        IO::out8(0xe9, characters[i]);
-    return 0;
+    if (serial_debug)
+        serial_putch(ch);
+    IO::out8(0xe9, ch);
 }
 
 static void debugger_putch(char*&, char ch)
 {
-    IO::out8(0xe9, ch);
+    debugger_out(ch);
+}
+
+extern "C" int dbgputstr(const char* characters, int length)
+{
+    for (int i = 0; i < length; ++i)
+        debugger_out(characters[i]);
+    return 0;
 }
 
 extern "C" int dbgprintf(const char* fmt, ...)

Kernel/kstdio.h

@@ -7,6 +7,8 @@ int dbgprintf(const char* fmt, ...);
 int dbgputstr(const char*, int);
 int kprintf(const char* fmt, ...);
 int ksprintf(char* buf, const char* fmt, ...);
+void set_serial_debug(bool on_or_off);
+int get_serial_debug();
 }
 
 #ifndef USERLAND