Week 09 Weekly Exercises

In this exercise, you are tasked with calling C code from within Rust!

You have been provided secretc.h, a header file which contains the definition of a secret C function: int secret_c_calculation(int x, double y, char z);

This is joined by libsecretc.a, the compiled C code ready to be linked through a Foreign Function Interface (FFI) with the Rust code!

You do not need to understand the C source code, and in-fact, we do not provide you the C source code. You are only required to call the C code from within Rust, and make use of the result it provides.

You will need to write both the C function definition (using the header file as a guideline) and call that C function from within main yourself.

The linking should already be taken care of for you (with a build.rs script and a #[link(...)] attribute), so if your code is written correctly, you should be able to simply use 6991 cargo as usual.

Note that since this exercise makes use of a pre-compiled C object file, we can only guarantee this exercise building correctly on x86_64-unknown-linux-gnu systems. This includes most Linux systems (including CSE) and most WSL installs, but not Windows itself nor MacOS. If you aren't running on a typical Linux system, you should work on this exercise on CSE (e.g. VLAB, SSH, lab machines, etc.). Although FFI generally works on many platforms, it is the C library in this case that restricts us to this target.

For example,

6991 cargo run -- 42 123.456 F
    Finished dev [unoptimized + debuginfo] target(s) in 0.00s
     Running `target/debug/rust2c 42 123.456 F`
The secret value is 176

When you think your program is working, you can use autotest to run some simple automated tests:

6991 autotest

When you are finished working on this exercise, you must submit your work by running give:

6991 give-crate

The recommended due date for this exercise is Week 10 Sunday 21:00:00.

You must run give before Week 10 Friday 17:00:00 to obtain the marks for this exercise. Note that this is an individual exercise; the work you submit with give must be entirely your own.

In this exercise, you have been provided the unsound_unsafe crate.

This crate attempts to (very dangerously) implement a singly-linked list data structure making liberal use of raw pointers instead of taking advantage of Rust's safety guarantees provided through its usual types (e.g. references).

Nevertheless, we are making use of this linked list, and it seems to generally work okay! We initialise a new linked list comprised of numbers given as command-line arguments, and perform the following operations:

• Print the list;
• Delete the first element in the list;
• Print the list again;
• Free the list.

Running the program with the list 1 2 3 can be observed as follows:

6991 cargo run -- 1 2 3
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/unsound_unsafe 1 2 3`
=== PRINTING LIST ===
1
2
3
=====================
=== PRINTING LIST ===
2
3
=====================

It seems that most of these operations work correctly (i.e. they are sound), however there appears to be a soundness issue when the list_delete_first function is called in the case of an already empty list! Users of our dangerous linked-list structure have reported segmentation faults in this specific scenario!

6991 cargo run --
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/unsound_unsafe`
=== PRINTING LIST ===
=====================
[1]    1402912 segmentation fault  6991 cargo run --

Your task is first to locate the unsoundness using Miri. Miri is already installed on CSE systems, so you can try running your code like such:

6991 cargo +nightly miri run -- 1 2 3
Preparing a sysroot for Miri (target: x86_64-unknown-linux-gnu)... done
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `/import/glass/1/cs6991/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo-miri runner target/miri/x86_64-unknown-linux-gnu/debug/foo 1 2 3`
=== PRINTING LIST ===
1
2
3
=====================
=== PRINTING LIST ===
2
3
=====================

Once you understand how to use Miri, try replicating the input demonstrating a segmentation fault from above in order to track down where this issue arises.

Finally, it's time to fix the unsoundness! You are only permitted to modify the list_delete_first function. You may not modify any other code.

Once you are satisfied that your code is most-likely sound, you should run it once again through Miri! Furthermore, the autotests for this exercise will test your code using Miri on a few different cases.

When you think your program is working, you can use autotest to run some simple automated tests:

6991 autotest

When you are finished working on this exercise, you must submit your work by running give:

6991 give-crate

The recommended due date for this exercise is Week 10 Sunday 21:00:00.

You must run give before Week 10 Friday 17:00:00 to obtain the marks for this exercise. Note that this is an individual exercise; the work you submit with give must be entirely your own.

In this exercise, we will be implementing our own simple Rc type.

Your task is to build a datastructure, called MyRc which has the following properties:

• The type should allow multiple people to own a value.
• The value should live until the last MyRc is dropped.
• The value should be dropped when the last MyRc is dropped.

There are hints for each function you should complete, in the starter code.

No changes to main.rs should be required, only lib.rs

You will need to write unsafe code in this activity - don't forget SAFETY comments! E.G the rust API guidelines

When you think your program is working, you can use autotest to run some simple automated tests:

6991 autotest

When you are finished working on this exercise, you must submit your work by running give:

6991 give-crate

The recommended due date for this exercise is Week 10 Sunday 21:00:00.

You must run give before Week 10 Friday 17:00:00 to obtain the marks for this exercise. Note that this is an individual exercise; the work you submit with give must be entirely your own.