factorize printf into io.h

1 files changed, 43 insertions, 0 deletions

diff --git a/include/io.h b/include/io.h
new file mode 100644
index 0000000..4b3ea4b
--- /dev/null
+++ b/include/io.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2020 Johannes Stoelp
+
+#pragma once
+
+#include "fmt.h"
+#include "syscall.h"
+
+#include <asm/unistd.h>
+
+// `dynld_printf` uses fixed-size buffer on the stack for formating the message
+// (since we don't impl buffered I/O).
+//
+// Size can be re-configured by defining `MAX_PRINTF_LEN` before including
+// `io.h`.
+//
+// NOTE: This allows to specify an arbitrarily large buffer on the stack, but
+// for the purpose of this study that's fine, we are cautious.
+#if !defined(MAX_PRINTF_LEN)
+#    define MAX_PRINTF_LEN 64
+#endif
+
+#define FD_STDOUT 1
+#define FD_STDERR 2
+
+int dynld_printf(const char* fmt, ...) {
+    char buf[MAX_PRINTF_LEN];
+
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = dynld_vsnprintf(buf, sizeof(buf), fmt, ap);
+    va_end(ap);
+
+    if (ret > MAX_PRINTF_LEN - 1) {
+        syscall3(__NR_write, FD_STDERR, buf, MAX_PRINTF_LEN - 1);
+
+        static const char warn[] = "\ndynld_printf: Message truncated, max length can be configured by defining MAX_PRINTF_LEN\n";
+        syscall3(__NR_write, FD_STDOUT, warn, sizeof(warn));
+        return MAX_PRINTF_LEN - 1;
+    }
+
+    syscall3(__NR_write, FD_STDOUT, buf, ret);
+    return ret;
+}