From bf5c0c7bfac1e6fde12d7c903c88c2632d8aa8fe Mon Sep 17 00:00:00 2001
From: Bryan Bernhart <[email protected]>
Date: Fri, 20 Feb 2026 13:26:41 -0800
Subject: [PATCH] WebNN: handle empty axes in ORT reverse operation

Previously, the ORT graph builder would attempt to generate a Slice node
with zero axes, which could lead to backend-specific crashes in certain
EPs. This CL ensures that empty axes are handled by emitting an Identity
node instead, maintaining spec compliance and preventing potential OOB
access during graph initialization.

Bug: 485203823
Change-Id: I80b310cb3609beb7907ab8ffbc823af1c6c74a90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7595579
Reviewed-by: Reilly Grant <[email protected]>
Commit-Queue: Bernhart, Bryan <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1588047}
---

diff --git a/services/webnn/ort/graph_builder_ort.cc b/services/webnn/ort/graph_builder_ort.cc
index 4126bbe..131a0046 100644
--- a/services/webnn/ort/graph_builder_ort.cc
+++ b/services/webnn/ort/graph_builder_ort.cc
@@ -2781,13 +2781,26 @@
 }
 
 void GraphBuilderOrt::AddReverseOperation(const mojom::Reverse& reverse) {
-  const std::string node_name = GenerateNodeName(reverse.label);
   const std::string input = GetOperandNameById(reverse.input_operand_id);
   const std::string output = GetOperandNameById(reverse.output_operand_id);
 
   CHECK(context_properties_.data_type_limits.reverse_input.Supports(
       GetOperand(reverse.input_operand_id).descriptor));
 
+  // Workaround: explicitly empty axes for a reverse operation should result in
+  // a no-op per spec. But we map this to an Identity node to prevent ORT
+  // EPs from mishandling empty arrays.
+  if (reverse.axes.empty()) {
+    const std::string node_name = GenerateNodeName(base::JoinString(
+        {kInserted, kOpTypeIdentity, kToEmulate, reverse.label}, kUnderscore));
+    std::array<const char*, 1> inputs = {input.c_str()};
+    std::array<const char*, 1> outputs = {output.c_str()};
+    model_editor_.AddNode(kOpTypeIdentity, node_name, inputs, outputs);
+    return;
+  }
+
+  const std::string node_name = GenerateNodeName(reverse.label);
+
   // Axes can be empty, which means no dimensions are reversed.
   base::FixedArray<int64_t> axes(reverse.axes.begin(), reverse.axes.end());
   size_t axes_size = axes.size();