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

libaux/mprintf.c

@@ -1,28 +1,38 @@
-#include <malloc.h>
 #include <mprintf.h>
 #include <printf.h>
 #include <process_self.h>
 #include <stdarg.h>
+#include <stdatomic.h>
 #include <streams.h>
 #include <string.h>
 #include <system.h>
 
+static char mprintf_buffer[MPRINTF_BUF_MAX];
+static atomic_flag mprintf_buffer_lock1 = ATOMIC_FLAG_INIT;
+
+static void mprintf_buffer_lock (void) {
+  while (atomic_flag_test_and_set_explicit (&mprintf_buffer_lock1, memory_order_acquire)) {
+#if defined(__x86_64__)
+    __asm__ volatile ("pause" ::: "memory");
+#endif
+  }
+}
+
+static void mprintf_buffer_unlock (void) {
+  atomic_flag_clear_explicit (&mprintf_buffer_lock1, memory_order_release);
+}
+
 void mprintf (const char* fmt, ...) {
   va_list args;
   va_start (args, fmt);
 
-  char* buf = malloc (MPRINTF_BUF_MAX);
+  mprintf_buffer_lock ();
 
-  if (buf == NULL) {
-    va_end (args);
-    return;
-  }
-
-  memset (buf, 0, MPRINTF_BUF_MAX);
-  int len = vsnprintf (buf, MPRINTF_BUF_MAX, fmt, args);
+  int len = vsnprintf (mprintf_buffer, MPRINTF_BUF_MAX, fmt, args);
 
   va_end (args);
 
-  stream_write (process_get_pgid (), STREAM_OUT, buf, len);
-  free (buf);
+  stream_write (process_get_pgid (), STREAM_OUT, mprintf_buffer, len);
+
+  mprintf_buffer_unlock ();
 }