fromrayquery-invoke-without-shader-table

Status: shipped (Phase 4) — see CHANGELOG.

(via ADR 0010)

What it detects

A dx::HitObject::FromRayQuery(...) value passed to Invoke(...) without an intervening SetShaderTableIndex(...) call on the same HitObject on every CFG path between construction and invocation. The SER spec requires FromRayQuery-constructed HitObjects to carry an explicit shader-table index before they can be invoked — the inline RayQuery does not record one because it has no concept of a shader table at traversal time. The Phase 4 definite-assignment analysis walks the CFG between construction and invocation.

Why it matters on a GPU

HitObject::FromRayQuery constructs a HitObject from the result of an inline RayQuery::TraceRayInline + Proceed traversal. The inline traversal does not consult a shader binding table — that is the whole point of the inline path — so the resulting HitObject has no shader-table index field set. When the application then wants to invoke a hit / miss shader through the SER path, it needs to tell the runtime which shader to dispatch; that's SetShaderTableIndex.

Calling Invoke on a FromRayQuery-constructed HitObject without setting the shader-table index is undefined behaviour. On NVIDIA Ada Lovelace, the runtime's behaviour depends on the driver: some versions silently dispatch shader 0; some fault. AMD RDNA 4's SER implementation behaves similarly, with vendor-dependent recovery. There is no clean error message at runtime; the lint catches the violation by walking the CFG between the two calls and verifying that every path has an intervening SetShaderTableIndex.

The fix is to insert the missing call. The diagnostic names the offending CFG path and points at the spec.

Examples

Bad

hlsl

// FromRayQuery -> Invoke without SetShaderTableIndex — UB.
[shader("raygeneration")]
void RayGen() {
    RayQuery<RAY_FLAG_FORCE_OPAQUE> q;
    q.TraceRayInline(g_BVH, 0, 0xFF, MakeRay());
    while (q.Proceed()) {}
    if (q.CommittedStatus() == COMMITTED_TRIANGLE_HIT) {
        dx::HitObject hit = dx::HitObject::FromRayQuery(q);
        // missing hit.SetShaderTableIndex(...)
        hit.Invoke(/*payload*/);                          // ERROR: no STI
    }
}

Good

hlsl

[shader("raygeneration")]
void RayGen() {
    RayQuery<RAY_FLAG_FORCE_OPAQUE> q;
    q.TraceRayInline(g_BVH, 0, 0xFF, MakeRay());
    while (q.Proceed()) {}
    if (q.CommittedStatus() == COMMITTED_TRIANGLE_HIT) {
        dx::HitObject hit = dx::HitObject::FromRayQuery(q);
        hit.SetShaderTableIndex(GetHitGroupIndex(q));     // required
        hit.Invoke(/*payload*/);
    }
}

Options

none

Fix availability

none — The right shader-table index is application-specific; the diagnostic names the missing call.

fromrayquery-invoke-without-shader-table ​

What it detects ​

Why it matters on a GPU ​

Examples ​

Bad ​

Good ​

Options ​

Fix availability ​

See also ​