3 files changed, 37 insertions, 8 deletions
diff --git a/lib/include/common.h b/lib/include/common.h
new file mode 100644
index 0000000..5ea6050
--- /dev/null
+++ b/lib/include/common.h
@@ -0,0 +1,16 @@
+// Copyright (c) 2020 Johannes Stoelp
+
+#pragma once
+
+#include "io.h"
+#include "syscall.h"
+
+#include <asm/unistd.h>
+
+#define ERROR_ON(cond, ...)         \
+    do {                            \
+        if ((cond)) {               \
+            efmt(__VA_ARGS__);      \
+            syscall1(__NR_exit, 1); \
+        }                           \
+    } while (0)
diff --git a/lib/include/io.h b/lib/include/io.h
index 5ca78a3..0f8b900 100644
--- a/lib/include/io.h
+++ b/lib/include/io.h
@@ -3,3 +3,4 @@
 #pragma once
 
 int pfmt(const char* fmt, ...);
+int efmt(const char* fmt, ...);
diff --git a/lib/src/io.c b/lib/src/io.c
index efe938b..b5e0dc5 100644
--- a/lib/src/io.c
+++ b/lib/src/io.c
@@ -16,22 +16,34 @@
 #define FD_STDOUT 1
 #define FD_STDERR 2
 
-int pfmt(const char* fmt, ...) {
+static int vdfmt(int fd, const char* fmt, va_list ap) {
     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);
+        syscall3(__NR_write, fd, 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));
+        syscall3(__NR_write, FD_STDERR, warn, sizeof(warn));
         return MAX_PRINTF_LEN - 1;
     }
 
-    syscall3(__NR_write, FD_STDOUT, buf, ret);
+    syscall3(__NR_write, fd, buf, ret);
+    return ret;
+}
+
+int pfmt(const char* fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = vdfmt(FD_STDOUT, fmt, ap);
+    va_end(ap);
+    return ret;
+}
+
+int efmt(const char* fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    int ret = vdfmt(FD_STDERR, fmt, ap);
+    va_end(ap);
     return ret;
 }