Add checked per-block scalar output witnesses by tpn · Pull Request #1585 · NVIDIA/cuda-rust

tpn · 2026-10-21T04:12:50Z

Kernels can write one scalar per block through DisjointSlice<T, BlockIndex>. thread::block_index() gives only thread (0, 0, 0) a scoped witness, with blocks numbered X-first across 1D, 2D and 3D grids. Checked get_mut handles short or empty outputs. This supplies block reductions with a safe output carrier; the caller still must produce a valid result.

This draft uses the reconstructed compiler on Rust 1.99.1 and depends on #1581. Review the owning diff: 10 files. GitHub's main-based Files tab includes prerequisites. A narrow stacked base requires an upstream parent branch or prerequisite landing.

Validation: current host/macro tests, compile-fail cases, rustdoc and strict Clippy pass. A standalone Git-installed compiler passes full/short/empty XYZ outputs, helper forwarding and owned async launches: 10 launches and 55 values, plus memcheck, racecheck and synccheck. A fresh HTTPS installation builds the same fixture and matches all four mapped executable sections, typed signatures and resource records. Whole CUBINs differ; the HTTPS binary was not run on GPU. The older baseline's instruction differences remain recorded.

With `lto = "fat"` or `lto = "thin"`, the build of a binary that uses a library with kernels stopped with an error: "failed to get bitcode from object file for LTO (Can't find section .llvmbc)". rustc keeps a list of the Rust objects in each rlib. This list contains the objects of all modules. With LTO, rustc reads bitcode from these objects and removes them from the link. The artifact objects have no bitcode. If a session writes an rlib, the backend now gives each artifact object to rustc as the DWARF object of its module. This object is in the rlib, but it is not in the list. LTO does not read this object, and the linker gets it from the rlib. The system linker does not get the DWARF objects. If the session also writes a binary or a dynamic library, the backend gives the artifact objects to this linker as link arguments. With `-Zlink-native-libraries=no`, rustc does not give link arguments to the linker. Then the artifact objects of this session are Rust objects, as before. The book said that `join_codegen()` and `link()` only call the LLVM backend. Now it tells what they add to the outputs. CI builds `cuda_module_in_lib` with fat LTO. The library is an rlib, and then an rlib and a cdylib. After each build, CI makes sure that the binary has the PTX bundles of the library and of the binary. It also makes sure that the cdylib has the PTX bundle of the library. Fixes NVIDIA#1495 Signed-off-by: Mikhail Borisov <mikhail.boriso2014@gmail.com> Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Use Cargo target names for standalone emit-ltoir artifacts. Bind the compiler and reader to the same intermediate directory when invoked from a Cargo workspace member. Signed-off-by: Trent Nelson <trent@trent.me>

Accept ordered external LTO files when materializing embedded cubins. Include their content in the codegen fingerprint and verify owned bytes before linking through the existing finalizer. Preserve inputs that overlap generated output paths and diagnose unresolved device symbols. Add a standalone CUDA FFI example and a native regression script. Signed-off-by: Trent Nelson <trent@trent.me>

Reuse existing example dependency pins and classify external LTO as an FFI fixture. Run its linking regression in native sweeps and verify relocatable debug output in the existing full-debug route. Signed-off-by: Trent Nelson <trent@trent.me>

Preserve exact geometry and fixed dynamic shared-memory requirements through artifact loading so preparation can select and validate the compiled allocation. Keep artifact writers and readers on one in-tree implementation while preserving legacy bundles without launch facts. Signed-off-by: Trent Nelson <trent@trent.me>

Combine the reviewed compiler prerequisites for native library calls. Keep the external LTO fixture on the shared in-tree artifact implementation. Signed-off-by: Trent Nelson <trent@trent.me>

Use the reviewed Cargo target and output-directory correction in the combined compiler prerequisite tree. Signed-off-by: Trent Nelson <trent@trent.me>

Resolve concrete registration functions and scalar argument types during device compilation, then invoke the native provider and link its owned LTO output through the ordinary artifact finalizer. Signed-off-by: Trent Nelson <trent@trent.me>