steps argument in Mat::new_nd_with_data() has a wrong type

[jerry73204]

The Mat::new_nd_with_data (doc) has a steps argument with type &size_t. I passed &0, the suggested default value, and it failed with the message.

Error: OpenCV(4.5.1) /build/opencv/src/opencv-4.5.1/modules/core/src/matrix.cpp:259: error: (-13:Image step is wrong) Step 7954887940465321323 for dimension 1 must be a multiple of esz1 4 in function 'setSize'
 (code: -13)

Look like it treats the reference as an integer. I guess the argument should have the type size_t,

[jerry73204]

Also new_nd_vec_with_data has this issue.

[twistedfall]

I think it expects a null pointer, not a pointer to null. Can you please try passing something like prt::null_ptr().as_ref() for steps? I’ll try to improve generation in this are in any case

[jerry73204]

It won't work. pointer.as_ref() returns None when it is null.

[twistedfall]

You’re right! Well, some kind of mem::transmute should do the trick, but yeah, it needs some fixing.

[jerry73204]

It is my workaround to pass null pointer as reference. Unfortunately, it passes the tests in in debug build but is killed by SIGILL in release build.

use platform_types::size_t;
let step: &size_t = mem::transmute(ptr::null() as *const size_t);
core::Mat::new_nd_with_data(&size, typ, tensor.data_ptr(), step)?

This is my implementation FYI.
https://github.com/jerry73204/rust-cv-convert/blob/46136573897146f1ea183772b4daeee5ffecab97/src/with_opencv_tch.rs#L347-L357

[twistedfall]

In my tests it literally generates the asm UD2 instruction starting with opt-level = 1. I suppose it has to do with the fact that references are guaranteed to be non-null in rust, so such transmute is instant UB. So it looks like there is no workaround. I'll try to make the fix asap.

[jerry73204]

Interesting, TIL there is a x86 instruction causes undefined behavior.

[twistedfall]

Can you please check the rel branch and confirm it fixes the problem for you? The steps argument is now Option<&[size_t]> so passing None should work.

[jerry73204]

Great. It passes every test even in release build.

[twistedfall]

It's now released in v0.49.0