Kernel: Add basic fixed width allocator for userspace

We have to move process stacks to the general heap and maybe map
kernel to higher half.

libc/stdlib.cpp

@@ -1,8 +1,10 @@
 #include <BAN/Assert.h>
 #include <ctype.h>
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/syscall.h>
 #include <unistd.h>
 
 extern "C" void _fini();
@@ -55,9 +57,15 @@ char* getenv(const char*)
 	return nullptr;
 }
 
-void* malloc(size_t)
+void* malloc(size_t bytes)
 {
-	return nullptr;	
+	long ret = syscall(SYS_ALLOC, bytes);
+	if (ret < 0)
+	{
+		errno = -ret;
+		return nullptr;
+	}
+	return (void*)ret;
 }
 
 void* calloc(size_t nmemb, size_t size)

libc/unistd.cpp

@@ -68,6 +68,12 @@ long syscall(long syscall, ...)
 			ret = Kernel::syscall(SYS_OPEN, path, oflags);
 			break;
 		}
+		case SYS_ALLOC:
+		{
+			size_t bytes = va_arg(args, size_t);
+			ret = Kernel::syscall(SYS_ALLOC, bytes);
+			break;
+		}
 		default:
 			puts("LibC: Unhandeled syscall");
 	}