[executorch][native] Split engine host factories out of the PTN runners

backends/native/test/runtime/BUCK

@@ -8,16 +8,24 @@ non_fbcode_target(_kind = define_common_targets)
 
 fbcode_target(_kind = define_common_targets)
 
-# Engine-neutral PTN runner; each engine's runner binary adds make_engine_host().
+# Declares make_engine_host(), which each engine's host library defines.
+fbcode_target(
+    _kind = runtime.cxx_library,
+    name = "engine_host",
+    exported_headers = ["PtnRunner.h"],
+    visibility = ["//executorch/backends/native/test/..."],
+    exported_deps = ["//executorch/backends/native/runtime/engine:engine"],
+)
+
+# Engine-neutral PTN runner; each engine's runner binary adds its host library.
 fbcode_target(
     _kind = runtime.cxx_library,
     name = "ptn_runner_main",
     srcs = ["ptn_runner_main.cpp"],
-    exported_headers = ["PtnRunner.h"],
     link_whole = True,
     undefined_symbols = True,
     visibility = ["//executorch/backends/native/test/..."],
-    exported_deps = ["//executorch/backends/native/runtime/engine:engine"],
+    exported_deps = [":engine_host"],
     deps = [
         "//executorch/backends/native/runtime:runtime",
         "//executorch/backends/native/runtime/deserialize:package",

backends/native/test/runtime/PtnRunner.h

@@ -12,8 +12,8 @@
 
 namespace ptn::testing {
 
-// Defined once per runner binary; ptn_runner_main.cpp drives the host it
-// returns, so every engine runs a PTN through the same harness.
+// Defined once per binary by an engine's host library; drivers such as
+// ptn_runner_main.cpp run every engine through the host it returns.
 std::unique_ptr<EngineHost> make_engine_host();
 
 } // namespace ptn::testing

backends/native/test/runtime/ggml/BUCK

@@ -59,17 +59,32 @@ _VARIANTS = [
     },
 ]
 
+[
+    fbcode_target(
+        _kind = runtime.cxx_library,
+        name = "ggml_engine_host" + v["suffix"],
+        srcs = ["ggml_ptn_runner.cpp"],
+        link_whole = True,
+        visibility = ["//executorch/backends/native/test/..."],
+        exported_deps = ["//executorch/backends/native/test/runtime:engine_host"],
+        deps = ["//executorch/backends/native/runtime/engine:" + v["engine"]] +
+               v.get("deps", []),
+        external_deps = ["gflags"] + v.get("external_deps", []),
+        labels = v.get("labels", []),
+        **v.get("compat", {})
+    )
+    for v in _VARIANTS
+]
+
 [
     fbcode_target(
         _kind = runtime.cxx_binary,
         name = "ggml_ptn_runner" + v["suffix"],
-        srcs = ["ggml_ptn_runner.cpp"],
         visibility = ["//executorch/backends/native/test/..."],
         deps = [
-            "//executorch/backends/native/runtime/engine:" + v["engine"],
+            ":ggml_engine_host" + v["suffix"],
             "//executorch/backends/native/test/runtime:ptn_runner_main",
-        ] + v.get("deps", []),
-        external_deps = ["gflags"] + v.get("external_deps", []),
+        ],
         labels = v.get("labels", []),
         **v.get("compat", {})
     )

backends/native/test/runtime/ggml/ggml_ptn_runner.cpp

@@ -4,7 +4,7 @@
 // This source code is licensed under the BSD-style license found in the
 // LICENSE file in the root directory of this source tree.
 
-// The ggml engine for ptn_runner_main.cpp.
+// The ggml engine host for PTN test drivers.
 
 #include <stdexcept>
 

backends/native/test/runtime/vulkan/targets.bzl

@@ -19,12 +19,20 @@ def define_common_targets():
         cmd = "mkdir -p $OUT && cp $(location fbsource//third-party/swiftshader/lib/linux-x64:libvk_swiftshader_so)/libvulkan.so.1 $OUT/libvk_swiftshader.so",
     )
 
+    runtime.cxx_library(
+        name = "vulkan_engine_host",
+        srcs = ["vulkan_ptn_runner.cpp"],
+        link_whole = True,
+        visibility = ["//executorch/backends/native/test/..."],
+        exported_deps = ["//executorch/backends/native/test/runtime:engine_host"],
+        deps = ["//executorch/backends/native/runtime/vulkan:vulkan_engine"],
+    )
+
     runtime.cxx_binary(
         name = "vulkan_ptn_runner",
-        srcs = ["vulkan_ptn_runner.cpp"],
         visibility = ["//executorch/backends/native/test/..."],
         deps = [
-            "//executorch/backends/native/runtime/vulkan:vulkan_engine",
+            ":vulkan_engine_host",
             "//executorch/backends/native/test/runtime:ptn_runner_main",
             "fbsource//third-party/swiftshader/lib/linux-x64:libvk_swiftshader_fbcode",
         ],

backends/native/test/runtime/vulkan/vulkan_ptn_runner.cpp

@@ -4,7 +4,7 @@
 // This source code is licensed under the BSD-style license found in the
 // LICENSE file in the root directory of this source tree.
 
-// The Vulkan engine for ptn_runner_main.cpp.
+// The Vulkan engine host for PTN test drivers.
 
 #include <executorch/backends/native/runtime/vulkan/VulkanEngine.h>
 #include <executorch/backends/native/test/runtime/PtnRunner.h>