1 files changed, 37 insertions, 0 deletions
diff --git a/lib/src/io.c b/lib/src/io.c
new file mode 100644
index 0000000..efe938b
--- /dev/null
+++ b/lib/src/io.c
@@ -0,0 +1,37 @@
+// Copyright (c) 2020 Johannes Stoelp
+
+#include <io.h>
+#include <fmt.h>
+#include <syscall.h>
+
+#include <asm/unistd.h>
+
+// `pfmt` uses fixed-size buffer on the stack for formating the message
+// (for simplicity and since we don't impl buffered I/O).
+//
+// NOTE: This allows to specify a large buffer on the stack, but for
+// the purpose of this study that's fine, we are cautious.
+#define MAX_PRINTF_LEN 128
+
+#define FD_STDOUT 1
+#define FD_STDERR 2
+
+int pfmt(const char* fmt, ...) {
+    char buf[MAX_PRINTF_LEN];
+
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = vfmt(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[] = "\npfmt: 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;
+}