add cargo-careful blog post

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+---
+title: "carego careful: run your Rust code with extra careful debug checking"
+categories: rust
+---
+
+Did you know that the standard library is full of useful checks that users never get to see?
+There are plenty of debug assertions in the standard library that will do things like check that `char::from_u32_unchecked` is called on a valid `char`, that `CStr::from_bytes_with_nul_unchecked` does not have internal nul bytes, or that pointer functions such as `read`, `copy`, or `copy_nonoverlapping` are called on suitably aligned non-null (and non-overlapping) pointers.
+However, the regular standard library that is distributed by rustup is compiled without debug assertions, so there is no easy way for users to benefit from all this extra checking.
+
+<!-- MORE -->
+
+[`cargo careful`](https://github.com/RalfJung/cargo-careful) is here to close this gap:
+when invoked the first time, it builds a standard library with debug assertions from source, and then runs your program or test suite with that standard library.
+Installing `cargo careful` is as easy as `cargo install cargo-careful`, and then you can do `cargo careful run`/`cargo careful test` to execute your binary crates and test suites with an extra amount of debug checking.
+
+This will naturally be slower than a regular debug or release build, but it is *much* faster than executing your program in [Miri](https://github.com/rust-lang/miri) and still helps find some Undefined Behavior.
+Unlike Miri, it is fully FFI-compatible (though the code behind the FFI barrier is completely unchecked).
+Of course Miri is much more thorough and `cargo careful` will miss many problems (for instance, it cannot detect out-of-bounds pointer arithmetic -- but it *does* perform bounds checking on `get_unchecked` slice accesses).
+
+Note that for now, some of these checks (in particular for raw pointer methods) cause an abrupt abort of the program via SIGILL without a nice error message or backtrace.
+There are probably ways to improve this in the future.
+Meanwhile, if you have some `unsafe` code that for one reason or another you cannot test with Miri, give [`cargo careful`] a try and let me know how it is doing. :)
+
+[`cargo careful`]: https://github.com/RalfJung/cargo-careful