Missing vulkan symbols from standard linux vulkan library?


#1

Some of the symbols declared in the vulkan headers (/usr/include/vulkan/*) are not defined in the vulkan library (libvulkan.so.1.1.82). (I’m on Ubuntu 18.04 using the standard vulkan packages, libvulkan1 and libvulkan-dev)

For example:

vkCreateInstance is declared in the vulkan headers, and defined in the vulkan library
vkCmdBeginConditionalRenderingEXT is declared in the vulkan headers, but is not defined in the vulkan library.

Why is that?

$ cat > t.cc 
#include <vulkan/vulkan.h>
int main() {
    { constexpr auto x = vkCmdBeginConditionalRenderingEXT; (void)x; }
}
^D
$ g++ t.cc -lvulkan
/tmp/cczuSwiY.o: In function `main':
t.cc:(.text+0x7): undefined reference to `vkCmdBeginConditionalRenderingEXT'
collect2: error: ld returned 1 exit status

The full list of such missing commands is: vkCmdBeginConditionalRenderingEXT, vkCmdBeginDebugUtilsLabelEXT, vkCmdBeginRenderPass2KHR, vkCmdDebugMarkerBeginEXT, vkCmdDebugMarkerEndEXT, vkCmdDebugMarkerInsertEXT, vkCmdDrawIndexedIndirectCountAMD, vkCmdDrawIndexedIndirectCountKHR, vkCmdDrawIndirectCountAMD, vkCmdDrawIndirectCountKHR, vkCmdEndConditionalRenderingEXT, vkCmdEndDebugUtilsLabelEXT, vkCmdEndRenderPass2KHR, vkCmdInsertDebugUtilsLabelEXT, vkCmdNextSubpass2KHR, vkCmdProcessCommandsNVX, vkCmdPushDescriptorSetKHR, vkCmdPushDescriptorSetWithTemplateKHR, vkCmdReserveSpaceForCommandsNVX, vkCmdSetCheckpointNV, vkCmdSetDiscardRectangleEXT, vkCmdSetSampleLocationsEXT, vkCmdSetViewportWScalingNV, vkCmdWriteBufferMarkerAMD, vkCreateDebugReportCallbackEXT, vkCreateDebugUtilsMessengerEXT, vkCreateIndirectCommandsLayoutNVX, vkCreateObjectTableNVX, vkCreateRenderPass2KHR, vkCreateValidationCacheEXT, vkDebugMarkerSetObjectNameEXT, vkDebugMarkerSetObjectTagEXT, vkDebugReportMessageEXT, vkDestroyDebugReportCallbackEXT, vkDestroyDebugUtilsMessengerEXT, vkDestroyIndirectCommandsLayoutNVX, vkDestroyObjectTableNVX, vkDestroyValidationCacheEXT, vkDisplayPowerControlEXT, vkGetFenceFdKHR, vkGetMemoryFdKHR, vkGetMemoryFdPropertiesKHR, vkGetMemoryHostPointerPropertiesEXT, vkGetPastPresentationTimingGOOGLE, vkGetPhysicalDeviceExternalImageFormatPropertiesNV, vkGetPhysicalDeviceGeneratedCommandsPropertiesNVX, vkGetPhysicalDeviceMultisamplePropertiesEXT, vkGetPhysicalDeviceSurfaceCapabilities2EXT, vkGetPhysicalDeviceSurfaceCapabilities2KHR, vkGetPhysicalDeviceSurfaceFormats2KHR, vkGetQueueCheckpointDataNV, vkGetRefreshCycleDurationGOOGLE, vkGetSemaphoreFdKHR, vkGetShaderInfoAMD, vkGetSwapchainCounterEXT, vkGetSwapchainStatusKHR, vkGetValidationCacheDataEXT, vkImportFenceFdKHR, vkImportSemaphoreFdKHR, vkMergeValidationCachesEXT, vkQueueBeginDebugUtilsLabelEXT, vkQueueEndDebugUtilsLabelEXT, vkQueueInsertDebugUtilsLabelEXT, vkRegisterDeviceEventEXT, vkRegisterDisplayEventEXT, vkRegisterObjectsNVX, vkReleaseDisplayEXT, vkSetDebugUtilsObjectNameEXT, vkSetDebugUtilsObjectTagEXT, vkSetHdrMetadataEXT, vkSubmitDebugUtilsMessageEXT, vkUnregisterObjectsNVX.


#2

My guess is because vkCreateInstance() is a core function that is always present. The other one is a conditional extension, and should really be obtained by dynamically asking for the pointer at run time. If the extension is not active there will never be a valid pointer for that function. Ideally, you should be dynamically asking the instance or device for all of their function pointer. A good driver will reduce the CUP calling overhead.