VK_EXT_robustness2

Other Extension Metadata

Last Modified Date

2020-01-29

IP Status

No known IP claims.

Contributors

• Liam Middlebrook, NVIDIA
• Jeff Bolz, NVIDIA

Description

This extension adds stricter requirements for how out of bounds reads and writes are handled. Most accesses must be tightly bounds-checked, out of bounds writes must be discarded, out of bound reads must return zero. Rather than allowing multiple possible (0,0,0,x) vectors, the out of bounds values are treated as zero, and then missing components are inserted based on the format as described in Component Substitution and vertex input attribute extraction.

These additional requirements may be expensive on some implementations, and should only be enabled when truly necessary.

This extension also adds support for null descriptors, where VK_NULL_HANDLE can be used instead of a valid handle. Accesses to null descriptors have well-defined behavior, and do not rely on robustness.

Promotion to VK_KHR_robustness2

All functionality in this extension is included in VK_KHR_robustness2, with the suffix changed to KHR. The original type, enum, and command names are still available as aliases of the core functionality.

New Structures

• Extending VkPhysicalDeviceFeatures2, VkDeviceCreateInfo:
  • VkPhysicalDeviceRobustness2FeaturesEXT
• Extending VkPhysicalDeviceProperties2:
  • VkPhysicalDeviceRobustness2PropertiesEXT

New Enum Constants

• VK_EXT_ROBUSTNESS_2_EXTENSION_NAME
• VK_EXT_ROBUSTNESS_2_SPEC_VERSION
• Extending VkStructureType:
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_ROBUSTNESS_2_FEATURES_EXT
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_ROBUSTNESS_2_PROPERTIES_EXT

Issues

1. Why do VkPhysicalDeviceRobustness2PropertiesEXT::robustUniformBufferAccessSizeAlignment and VkPhysicalDeviceRobustness2PropertiesEXT::robustStorageBufferAccessSizeAlignment exist?

RESOLVED: Some implementations cannot efficiently tightly bounds-check all buffer accesses. Rather, the size of the bound range is padded to some power of two multiple, up to 256 bytes for uniform buffers and up to 4 bytes for storage buffers, and that padded size is bounds-checked. This is sufficient to implement D3D-like behavior, because D3D only allows binding whole uniform buffers or ranges that are a multiple of 256 bytes, and D3D raw and structured buffers only support 32-bit accesses.

Examples

None.

Version History

• Revision 1, 2019-11-01 (Jeff Bolz, Liam Middlebrook)
  • Initial draft