Use static buffers for mprintf and debug_printf, cut down on library dependencies

libdebugconsole/debugconsole.c

@@ -1,10 +1,25 @@
 #include <debugconsole.h>
 #include <devices.h>
-#include <malloc.h>
 #include <printf.h>
+#include <stdatomic.h>
 #include <stddef.h>
 #include <system.h>
 
+static char debug_printf_buffer[DEBUG_PRINTF_MAX];
+static atomic_flag debug_printf_buffer_lock = ATOMIC_FLAG_INIT;
+
+static void debugconsole_printf_buffer_lock (void) {
+  while (atomic_flag_test_and_set_explicit (&debug_printf_buffer_lock, memory_order_acquire)) {
+#if defined(__x86_64__)
+    __asm__ volatile ("pause" ::: "memory");
+#endif
+  }
+}
+
+static void debugconsole_printf_buffer_unlock (void) {
+  atomic_flag_clear_explicit (&debug_printf_buffer_lock, memory_order_release);
+}
+
 int debugconsole_print (const char* string, size_t len) {
   return device_do ("debugconsole", DEBUGCONSOLE_PUTSTR, (void*)string, (void*)&len, NULL, NULL);
 }
@@ -13,18 +28,13 @@ void debug_printf (const char* fmt, ...) {
   va_list args;
   va_start (args, fmt);
 
-  char* buf = malloc (DEBUG_PRINTF_MAX);
+  debugconsole_printf_buffer_lock ();
 
-  if (buf == NULL) {
-    va_end (args);
-    return;
-  }
-
-  buf[0] = '\0';
-  int len = vsnprintf (buf, DEBUG_PRINTF_MAX, fmt, args);
+  int len = vsnprintf (debug_printf_buffer, DEBUG_PRINTF_MAX, fmt, args);
 
   va_end (args);
 
-  debugconsole_print (buf, len);
-  free (buf);
+  debugconsole_print (debug_printf_buffer, len);
+
+  debugconsole_printf_buffer_unlock ();
 }