1 files changed, 53 insertions, 0 deletions
diff --git a/rust/qemu-api/src/c_str.rs b/rust/qemu-api/src/c_str.rs
new file mode 100644
index 0000000000..4cd96da0b4
--- /dev/null
+++ b/rust/qemu-api/src/c_str.rs
@@ -0,0 +1,53 @@
+// Copyright 2024 Red Hat, Inc.
+// Author(s): Paolo Bonzini <pbonzini@redhat.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#[macro_export]
+/// Given a string constant _without_ embedded or trailing NULs, return
+/// a `CStr`.
+///
+/// Needed for compatibility with Rust <1.77.
+macro_rules! c_str {
+    ($str:expr) => {{
+        const STRING: &str = concat!($str, "\0");
+        const BYTES: &[u8] = STRING.as_bytes();
+
+        // "for" is not allowed in const context... oh well,
+        // everybody loves some lisp.  This could be turned into
+        // a procedural macro if this is a problem; alternatively
+        // Rust 1.72 makes CStr::from_bytes_with_nul a const function.
+        const fn f(b: &[u8], i: usize) {
+            if i == b.len() - 1 {
+            } else if b[i] == 0 {
+                panic!("c_str argument contains NUL")
+            } else {
+                f(b, i + 1)
+            }
+        }
+        f(BYTES, 0);
+
+        // SAFETY: absence of NULs apart from the final byte was checked above
+        unsafe { std::ffi::CStr::from_bytes_with_nul_unchecked(BYTES) }
+    }};
+}
+
+#[cfg(test)]
+mod tests {
+    use std::ffi::CStr;
+
+    use crate::c_str;
+
+    #[test]
+    fn test_cstr_macro() {
+        let good = c_str!("🦀");
+        let good_bytes = b"\xf0\x9f\xa6\x80\0";
+        assert_eq!(good.to_bytes_with_nul(), good_bytes);
+    }
+
+    #[test]
+    fn test_cstr_macro_const() {
+        const GOOD: &CStr = c_str!("🦀");
+        const GOOD_BYTES: &[u8] = b"\xf0\x9f\xa6\x80\0";
+        assert_eq!(GOOD.to_bytes_with_nul(), GOOD_BYTES);
+    }
+}