Pass through direct to driver for no-op intercepts

solidpixel · solidpixel · commit a89e9261b914 · 2025-08-13T22:53:37.000+01:00
diff --git a/generator/vk_codegen/device_dispatch_table.txt b/generator/vk_codegen/device_dispatch_table.txt
@@ -26,9 +26,14 @@ struct DeviceInterceptTableEntry
      * @brief The layer function pointer.
      */
     PFN_vkVoidFunction function;
+
+    /**
+     * @brief The layer default function pointer.
+     */
+    PFN_vkVoidFunction defaultFunction;
 };
 
-#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>) }
+#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<default_tag>) }
 
 /**
  * @brief The device dispatch table used to call the driver.
diff --git a/generator/vk_codegen/instance_dispatch_table.txt b/generator/vk_codegen/instance_dispatch_table.txt
@@ -27,9 +27,14 @@ struct InstanceInterceptTableEntry
      * @brief The layer function pointer.
      */
     PFN_vkVoidFunction function;
+
+    /**
+     * @brief The layer default function pointer.
+     */
+    PFN_vkVoidFunction defaultFunction;
 };
 
-#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>) }
+#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<default_tag>) }
 
 /**
  * @brief The instance dispatch table used to call the driver.
diff --git a/generator/vk_layer/source/instance.hpp b/generator/vk_layer/source/instance.hpp
@@ -128,7 +128,7 @@ class Instance
     VkInstance instance;
 
     /**
-     * @brief The next layer's \c vkGetInstanceProcAddr() function pointer.
+     * @brief The next layer's @c vkGetInstanceProcAddr() function pointer.
      */
     PFN_vkGetInstanceProcAddr nlayerGetProcAddress;
 
diff --git a/layer_example/source/instance.hpp b/layer_example/source/instance.hpp
@@ -122,7 +122,7 @@ class Instance
     VkInstance instance;
 
     /**
-     * @brief The next layer's \c vkGetInstanceProcAddr() function pointer.
+     * @brief The next layer's @c vkGetInstanceProcAddr() function pointer.
      */
     PFN_vkGetInstanceProcAddr nlayerGetProcAddress;
 
diff --git a/layer_gpu_profile/source/instance.hpp b/layer_gpu_profile/source/instance.hpp
@@ -123,7 +123,7 @@ class Instance
     VkInstance instance;
 
     /**
-     * @brief The next layer's \c vkGetInstanceProcAddr() function pointer.
+     * @brief The next layer's @c vkGetInstanceProcAddr() function pointer.
      */
     PFN_vkGetInstanceProcAddr nlayerGetProcAddress;
 
diff --git a/layer_gpu_support/source/instance.hpp b/layer_gpu_support/source/instance.hpp
@@ -122,7 +122,7 @@ class Instance
     VkInstance instance;
 
     /**
-     * @brief The next layer's \c vkGetInstanceProcAddr() function pointer.
+     * @brief The next layer's @c vkGetInstanceProcAddr() function pointer.
      */
     PFN_vkGetInstanceProcAddr nlayerGetProcAddress;
 
diff --git a/layer_gpu_timeline/source/instance.hpp b/layer_gpu_timeline/source/instance.hpp
@@ -122,7 +122,7 @@ class Instance
     VkInstance instance;
 
     /**
-     * @brief The next layer's \c vkGetInstanceProcAddr() function pointer.
+     * @brief The next layer's @c vkGetInstanceProcAddr() function pointer.
      */
     PFN_vkGetInstanceProcAddr nlayerGetProcAddress;
 
diff --git a/source_common/framework/device_dispatch_table.hpp b/source_common/framework/device_dispatch_table.hpp
@@ -51,9 +51,14 @@ struct DeviceInterceptTableEntry
      * @brief The layer function pointer.
      */
     PFN_vkVoidFunction function;
+
+    /**
+     * @brief The layer default function pointer.
+     */
+    PFN_vkVoidFunction defaultFunction;
 };
 
-#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>) }
+#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<default_tag>) }
 
 /**
  * @brief The device dispatch table used to call the driver.
diff --git a/source_common/framework/instance_dispatch_table.hpp b/source_common/framework/instance_dispatch_table.hpp
@@ -52,9 +52,14 @@ struct InstanceInterceptTableEntry
      * @brief The layer function pointer.
      */
     PFN_vkVoidFunction function;
+
+    /**
+     * @brief The layer default function pointer.
+     */
+    PFN_vkVoidFunction defaultFunction;
 };
 
-#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>) }
+#define ENTRY(fnc) { STR(fnc), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<user_tag>), reinterpret_cast<PFN_vkVoidFunction>(layer_##fnc<default_tag>) }
 
 /**
  * @brief The instance dispatch table used to call the driver.
diff --git a/source_common/framework/manual_functions.cpp b/source_common/framework/manual_functions.cpp
@@ -29,6 +29,7 @@
  * implemented as library code which can be swapped for alternative
  * implementations on a per-layer basis if needed.
  */
+
 #include <vulkan/utility/vk_struct_helper.hpp>
 
 #include "framework/manual_functions.hpp"
@@ -111,7 +112,35 @@ VkLayerDeviceCreateInfo* getChainInfo(const VkDeviceCreateInfo* pCreateInfo)
 }
 
 /* See header for documentation. */
-std::pair<bool, PFN_vkVoidFunction> getInstanceLayerFunction(const char* name)
+bool isFunctionAlwaysExported(const char* name)
+{
+    const std::array<const char*, 11> alwaysExportedFunctions {
+        "vkGetInstanceProcAddr",
+        "vkGetDeviceProcAddr",
+        "vkEnumerateInstanceExtensionProperties",
+        "vkEnumerateDeviceExtensionProperties",
+        "vkEnumerateInstanceLayerProperties",
+        "vkEnumerateDeviceLayerProperties",
+        "vkCreateInstance",
+        "vkDestroyInstance",
+        "vkCreateDevice",
+        "vkDestroyDevice",
+        "vkGetDeviceImageMemoryRequirementsKHR",
+    };
+
+    for (const char* functionName : alwaysExportedFunctions)
+    {
+        if (!strcmp(functionName, name))
+        {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+/* See header for documentation. */
+std::tuple<bool, PFN_vkVoidFunction, PFN_vkVoidFunction> getInstanceLayerFunction(const char* name)
 {
     const std::array<const char*, 5> globalFunctions {
         // Supported since Vulkan 1.0
@@ -125,7 +154,7 @@ std::pair<bool, PFN_vkVoidFunction> getInstanceLayerFunction(const char* name)
     };
 
     bool isGlobal {false};
-    for (const auto* globalName : globalFunctions)
+    for (const char* globalName : globalFunctions)
     {
         if (!strcmp(globalName, name))
         {
@@ -138,25 +167,25 @@ std::pair<bool, PFN_vkVoidFunction> getInstanceLayerFunction(const char* name)
     {
         if (!strcmp(function.name, name))
         {
-            return {isGlobal, function.function};
+            return std::make_tuple(isGlobal, function.function, function.defaultFunction);
         }
     }
 
-    return {isGlobal, nullptr};
+    return std::make_tuple(isGlobal, nullptr, nullptr);
 }
 
 /* See header for documentation. */
-PFN_vkVoidFunction getDeviceLayerFunction(const char* name)
+std::pair<PFN_vkVoidFunction, PFN_vkVoidFunction> getDeviceLayerFunction(const char* name)
 {
     for (auto& function : deviceIntercepts)
     {
         if (!strcmp(function.name, name))
         {
-            return function.function;
+            return {function.function, function.defaultFunction};
         }
     }
 
-    return nullptr;
+    return {nullptr, nullptr};
 }
 
 /* See header for documentation. */
@@ -497,7 +526,7 @@ void enableDeviceVkExtImageCompressionControl(Instance& instance,
 /** See Vulkan API for documentation. */
 PFN_vkVoidFunction layer_vkGetInstanceProcAddr_default(VkInstance instance, const char* pName)
 {
-    auto [isGlobal, layerFunction] = getInstanceLayerFunction(pName);
+    auto [isGlobal, layerFunction, layerDefaultFunction] = getInstanceLayerFunction(pName);
 
     // Global functions must be exposed and do not require the caller to pass
     // a valid instance pointer, although it is required to be nullptr in
@@ -507,6 +536,15 @@ PFN_vkVoidFunction layer_vkGetInstanceProcAddr_default(VkInstance instance, cons
         return layerFunction;
     }
 
+    // Function is not exported because layer doesn't implement it at all
+    bool exportLayerFunction { layerFunction != nullptr };
+
+    // Function is not exported because layer doesn't specialize a user_tag version
+    if (!isFunctionAlwaysExported(pName) && layerFunction == layerDefaultFunction)
+    {
+        exportLayerFunction = false;
+    }
+
     // For other functions, only expose functions that the driver exposes to
     // avoid changing queryable interface behavior seen by the application
     if (instance)
@@ -519,7 +557,7 @@ PFN_vkVoidFunction layer_vkGetInstanceProcAddr_default(VkInstance instance, cons
         PFN_vkVoidFunction driverFunction = layer->nlayerGetProcAddress(instance, pName);
 
         // If driver exposes it and the layer has one, use the layer function
-        if (driverFunction && layerFunction)
+        if (driverFunction && exportLayerFunction)
         {
             return layerFunction;
         }
@@ -542,10 +580,19 @@ PFN_vkVoidFunction layer_vkGetDeviceProcAddr_default(VkDevice device, const char
     // Only expose functions that the driver exposes to avoid changing
     // queryable interface behavior seen by the application
     auto driverFunction = layer->driver.vkGetDeviceProcAddr(device, pName);
-    auto layerFunction = getDeviceLayerFunction(pName);
+    auto [layerFunction, layerDefaultFunction] = getDeviceLayerFunction(pName);
+
+    // Function is not exported because layer doesn't implement it at all
+    bool exportLayerFunction { layerFunction != nullptr };
+
+    // Function is not exported because layer doesn't specialize a user_tag version
+    if (!isFunctionAlwaysExported(pName) && layerFunction == layerDefaultFunction)
+    {
+        exportLayerFunction = false;
+    }
 
     // If driver exposes it and the layer has one, use the layer function
-    if (driverFunction && layerFunction)
+    if (driverFunction && exportLayerFunction)
     {
         return layerFunction;
     }
diff --git a/source_common/framework/manual_functions.hpp b/source_common/framework/manual_functions.hpp
@@ -44,6 +44,7 @@
 #include <mutex>
 #include <string>
 #include <thread>
+#include <tuple>
 #include <utility>
 #include <vector>
 
@@ -66,17 +67,18 @@ VkLayerInstanceCreateInfo* getChainInfo(const VkInstanceCreateInfo* pCreateInfo)
 VkLayerDeviceCreateInfo* getChainInfo(const VkDeviceCreateInfo* pCreateInfo);
 
 /**
- * @brief Fetch the function for a given static instance entrypoint name.
+ * @brief Is this function always exported by the layer?
  *
- * This function is used for finding the fixed entrypoints that must exist and
- * that can return a valid function pointer without needing a created instance.
+ * When optimizing entrypoints the layer will not use the layer function
+ * if no user_tag variant exists, unless the function is marked as always
+ * exported.
  *
  * @param name   The Vulkan function name.
  *
- * @return The layer function pointer, or \c nullptr if the layer doesn't
- *         intercept the function.
+ * @return @c true if default implementation is always exported, @c false if
+ *         only @c <user_tag> specializations are exported .
  */
-PFN_vkVoidFunction getFixedInstanceLayerFunction(const char* name);
+bool isFunctionAlwaysExported(const char* name);
 
 /**
  * @brief Fetch the function for a given dynamic instance entrypoint name.
@@ -86,11 +88,12 @@ PFN_vkVoidFunction getFixedInstanceLayerFunction(const char* name);
  *
  * @param name   The Vulkan function name.
  *
- * @return Boolean indicating if this is a globally accessible function, and
- *         the layer function pointer, or \c nullptr if the layer doesn't
- *         intercept the function.
+ * @return Boolean indicating if this is a globally accessible function, the
+ *         active the layer function pointer, and the default layer function
+ *         pointer. Returns @c nullptr for the function pointers if the layer
+ *         doesn't implement an intercept for the function.
  */
-std::pair<bool, PFN_vkVoidFunction> getInstanceLayerFunction(const char* name);
+std::tuple<bool, PFN_vkVoidFunction, PFN_vkVoidFunction> getInstanceLayerFunction(const char* name);
 
 /**
  * @brief Fetch the function for a given dynamic instance entrypoint name.
@@ -100,10 +103,11 @@ std::pair<bool, PFN_vkVoidFunction> getInstanceLayerFunction(const char* name);
  *
  * @param name   The Vulkan function name.
  *
- * @return The layer function pointer, or \c nullptr if the layer doesn't
- *         intercept the function.
+ * @return The active the layer function pointer, and the default layer
+ *         function pointer. Returns @c nullptr for the function pointers if
+ *         the layer doesn't implement an intercept for the function.
  */
-PFN_vkVoidFunction getDeviceLayerFunction(const char* name);
+std::pair<PFN_vkVoidFunction, PFN_vkVoidFunction> getDeviceLayerFunction(const char* name);
 
 /**
  * @brief Fetch the maximum supported instance API version.
diff --git a/source_common/framework/utils.hpp b/source_common/framework/utils.hpp
@@ -61,11 +61,22 @@
 using APIVersion = std::pair<uint32_t, uint32_t>;
 
 /**
- * @brief Tag type used for template function dispatch;
+ * @brief Tag type used for template function dispatch.
+ *
+ * Layer-specified intercepts implemented for a specific layer must use
+ * user_tag type for their specializations to ensure that their version of
+ * the function is selected.
  */
-struct user_tag
-{
-};
+struct user_tag {};
+
+/**
+ * @brief Tag type used for template function dispatch.
+ *
+ * Layer-specified intercepts implemented for a specific layer must NOT use
+ * default_tag type for their specializations. This is a dummy tag used in the
+ * dispatch logic that will not match a layer-specific specialization.
+ */
+struct default_tag {};
 
 /**
  * @brief Convert a dispatchable API handle to the underlying dispatch key.
