Attribute Macro warp_kernel 

#[warp_kernel]

Mark a function as a GPU kernel entry point.

This attribute transforms the function signature for PTX compilation:

• Adds #[no_mangle] for symbol visibility in PTX
• Adds extern "ptx-kernel" ABI
• Wraps the body in unsafe (PTX kernels are inherently unsafe)

Parameter Rules

Kernel parameters must be one of:

• Raw pointers (*const T, *mut T) — for device memory
• Scalars (u8, u16, u32, u64, i8, i16, i32, i64, f32, f64, bool) — passed by value

Note: usize/isize are rejected because their width is platform-dependent. On nvptx64 they are 64-bit, but the host launcher may assume a different size, causing ABI mismatch. Use explicit-width types (u32, u64, etc.) instead.

Compile-Time Safety

The function body uses warp-types normally. Warp::kernel_entry() creates the initial Warp<All>, and the type system prevents shuffle-from-inactive-lane bugs at compile time — on the actual GPU target.