On Tue, Nov 19, 2024 at 12:27 AM Steven Rostedt [off-list ref] wrote:

On Mon, 18 Nov 2024 20:27:26 +0000
Alice Ryhl [off-list ref] wrote:

quoted

When building the rust_print sample with CONFIG_JUMP_LABEL=n, the Rust
static key support falls back to using static_key_count. This function
accepts a mutable pointer to the `struct static_key`, but the Rust
abstractions are incorrectly passing a const pointer.

This means that builds using CONFIG_JUMP_LABEL=n and SAMPLE_RUST_PRINT=y
fail with the following error message:

      error[E0308]: mismatched types
        --> <root>/samples/rust/rust_print_main.rs:87:5
         |
      87 | /     kernel::declare_trace! {
      88 | |         /// # Safety
      89 | |         ///
      90 | |         /// Always safe to call.
      91 | |         unsafe fn rust_sample_loaded(magic: c_int);
      92 | |     }
         | |     ^
         | |     |
         | |_____types differ in mutability
         |       arguments to this function are incorrect
         |
         = note: expected raw pointer `*mut kernel::bindings::static_key`
                    found raw pointer `*const kernel::bindings::static_key`
      note: function defined here
        --> <root>/rust/bindings/bindings_helpers_generated.rs:33:12
         |
      33 |     pub fn static_key_count(key: *mut static_key) -> c_int;
         |            ^^^^^^^^^^^^^^^^

To fix this, insert a pointer cast so that the pointer is mutable.

Hi Alice,

BTW, how do you test the sample tracepoint? I see you add a tracepoint in
the module load call, but currently we can enable module tracepoints on
module load. How do you enable it when the rust_print module gets loaded?

I've only really used the sample in this series as a build test. The
bulk of my testing has occurred by using this tracepoint support in
Rust Binder where I have 30 different tracepoints and I've been able
to verify that I can enable them and so on there.

Alice