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rust: introduce a c_str macro
This allows CStr constants to be defined easily on Rust 1.63.0, while checking that there are no embedded NULs. c"" literals were only stabilized in Rust 1.77.0. Reviewed-by: Zhao Liu <zhao1.liu@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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8 changed files with 78 additions and 19 deletions
53
rust/qemu-api/src/c_str.rs
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53
rust/qemu-api/src/c_str.rs
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// Copyright 2024 Red Hat, Inc.
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// Author(s): Paolo Bonzini <pbonzini@redhat.com>
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// SPDX-License-Identifier: GPL-2.0-or-later
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#[macro_export]
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/// Given a string constant _without_ embedded or trailing NULs, return
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/// a `CStr`.
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///
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/// Needed for compatibility with Rust <1.77.
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macro_rules! c_str {
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($str:expr) => {{
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const STRING: &str = concat!($str, "\0");
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const BYTES: &[u8] = STRING.as_bytes();
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// "for" is not allowed in const context... oh well,
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// everybody loves some lisp. This could be turned into
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// a procedural macro if this is a problem; alternatively
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// Rust 1.72 makes CStr::from_bytes_with_nul a const function.
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const fn f(b: &[u8], i: usize) {
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if i == b.len() - 1 {
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} else if b[i] == 0 {
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panic!("c_str argument contains NUL")
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} else {
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f(b, i + 1)
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}
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}
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f(BYTES, 0);
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// SAFETY: absence of NULs apart from the final byte was checked above
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unsafe { std::ffi::CStr::from_bytes_with_nul_unchecked(BYTES) }
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}};
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}
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#[cfg(test)]
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mod tests {
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use std::ffi::CStr;
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use crate::c_str;
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#[test]
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fn test_cstr_macro() {
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let good = c_str!("🦀");
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let good_bytes = b"\xf0\x9f\xa6\x80\0";
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assert_eq!(good.to_bytes_with_nul(), good_bytes);
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}
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#[test]
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fn test_cstr_macro_const() {
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const GOOD: &CStr = c_str!("🦀");
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const GOOD_BYTES: &[u8] = b"\xf0\x9f\xa6\x80\0";
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assert_eq!(GOOD.to_bytes_with_nul(), GOOD_BYTES);
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}
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}
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