Made the cstr!() macro usable in const contexts

Author: alex

src/lib.rs

@@ -1,5 +1,5 @@
 #![no_std]
-#![feature(allocator_api, alloc_error_handler, const_fn)]
+#![feature(allocator_api, alloc_error_handler, const_fn, const_raw_ptr_deref)]
 
 extern crate alloc;
 

src/types.rs

@@ -18,11 +18,11 @@ impl Mode {
 pub struct CStr(str);
 
 impl CStr {
-    pub fn new(data: &str) -> &CStr {
-        if data.bytes().position(|b| b == b'\x00') != Some(data.len() - 1) {
-            panic!("CStr must contain a single NUL byte at the end");
-        }
-        unsafe { &*(data as *const str as *const CStr) }
+    /// Creates a new CStr from a str without performing any additional checks. `data` _must_ end
+    /// with a NUL byte, and should only have only a single NUL byte, or the string will be
+    /// truncated.
+    pub const unsafe fn new_unchecked(data: &str) -> &CStr {
+        &*(data as *const str as *const CStr)
     }
 }
 
@@ -34,9 +34,15 @@ impl Deref for CStr {
     }
 }
 
+/// Creates a new `CStr` from a string literal. The string literal should not contain any NUL
+/// bytes. Example usage:
+/// ```
+/// const MY_CSTR: &CStr = cstr!("My awesome CStr!");
+/// ```
 #[macro_export]
 macro_rules! cstr {
     ($str:expr) => {{
-        $crate::CStr::new(concat!($str, "\x00"))
+        let s = concat!($str, "\x00");
+        unsafe { $crate::CStr::new_unchecked(s) }
     }};
 }

tests/utils/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "utils-tests"
+version = "0.1.0"
+authors = ["Alex Gaynor <alex.gaynor@gmail.com>", "Geoffrey Thomas <geofft@ldpreload.com>"]
+edition = "2018"
+
+[lib]
+crate-type = ["staticlib"]
+test = false
+
+[features]
+default = ["linux-kernel-module"]
+
+[dependencies]
+linux-kernel-module = { path = "../..", optional = true }
+
+[dev-dependencies]
+kernel-module-testlib = { path = "../../testlib" }

tests/utils/src/lib.rs

@@ -0,0 +1,22 @@
+#![no_std]
+#![feature(const_str_as_bytes)]
+
+use linux_kernel_module;
+
+struct UtilsTestModule;
+
+#[allow(dead_code)]
+const TEST_CSTR: &linux_kernel_module::CStr = linux_kernel_module::cstr!("abc");
+
+impl linux_kernel_module::KernelModule for UtilsTestModule {
+    fn init() -> linux_kernel_module::KernelResult<Self> {
+        Ok(UtilsTestModule)
+    }
+}
+
+linux_kernel_module::kernel_module!(
+    UtilsTestModule,
+    author: "Fish in a Barrel Contributors",
+    description: "A module for testing various utilities",
+    license: "GPL"
+);

tests/utils/tests/tests.rs

@@ -0,0 +1,6 @@
+use kernel_module_testlib::with_kernel_module;
+
+#[test]
+fn test_module_loads() {
+    with_kernel_module(|| {});
+}