Library Forwarding/vulkan: Reload pointers for extension functions more aggressively

Some applications create multiple Vulkan instances with different sets of
extensions. We might hence miss some of these pointers during the initial
function pointer query.

ThunkLibs/libvulkan/Host.cpp

@@ -37,7 +37,7 @@ static void DoSetupWithInstance(VkInstance instance) {
     std::abort();
   }
 
-  // Query pointers for functions customized below
+  // Query pointers for non-EXT functions customized below
   (void*&)LDR_PTR(vkCreateDevice) = (void*)LDR_PTR(vkGetInstanceProcAddr)(instance, "vkCreateDevice");
 
   // Only do this lookup once.
@@ -240,6 +240,25 @@ static PFN_vkVoidFunction FEXFN_IMPL(vkGetInstanceProcAddr)(VkInstance a_0, cons
 
   // Check for functions with custom implementations first
   if (auto ptr = LookupCustomVulkanFunction(a_1)) {
+    // If this function belongs to an instance extension, requery its address.
+    // This ensures fexldr_ptr_* is valid if the application creates a minimal
+    // VkInstance with no extensions before creating its actual instance.
+    using namespace std::string_view_literals;
+    if (a_1 == "vkGetRandROutputDisplayEXT"sv && !LDR_PTR(vkGetRandROutputDisplayEXT)) {
+      (void*&)LDR_PTR(vkGetRandROutputDisplayEXT) = (void*)LDR_PTR(vkGetInstanceProcAddr)(a_0, "vkGetRandROutputDisplayEXT");
+    }
+    if (a_1 == "vkAcquireXlibDisplayEXT"sv && !LDR_PTR(vkAcquireXlibDisplayEXT)) {
+      (void*&)LDR_PTR(vkAcquireXlibDisplayEXT) = (void*)LDR_PTR(vkGetInstanceProcAddr)(a_0, "vkAcquireXlibDisplayEXT");
+    }
+    const char* XcbPresent = "vkGetPhysicalDeviceXcbPresentationSupportKHR";
+    if (a_1 == std::string_view {XcbPresent} && !LDR_PTR(vkGetPhysicalDeviceXcbPresentationSupportKHR)) {
+      (void*&)LDR_PTR(vkGetPhysicalDeviceXcbPresentationSupportKHR) = (void*)LDR_PTR(vkGetInstanceProcAddr)(a_0, XcbPresent);
+    }
+    const char* XlibPresent = "vkGetPhysicalDeviceXlibPresentationSupportKHR";
+    if (a_1 == std::string_view {XlibPresent} && !LDR_PTR(vkGetPhysicalDeviceXlibPresentationSupportKHR)) {
+      (void*&)LDR_PTR(vkGetPhysicalDeviceXlibPresentationSupportKHR) = (void*)LDR_PTR(vkGetInstanceProcAddr)(a_0, XlibPresent);
+    }
+
     return ptr;
   }