Add mode/option to validate dispatchable handles... about vulkan-loader HOT 7 CLOSED

To avoid a performance impact, maybe we could provide an alternative libvulkan.so to link against?
The debug library could do the validation check on the dispatch object before calling down the chain.
And for production the application use the standard library that does not include the check.

from vulkan-loader.

This seems to be a corner case even for debugging and validation. But certainly a separate build of the loader, or a mode of operation for the loader would be among the ways to implement it.

from vulkan-loader.

@jzulauf-lunarg How would app code enable such a mode? Through a new validation layer? Or did you have something else in mind?

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Can't be a layer AFAICT. The loader itself is trying to use these handles in order to dispatch to the layers. As for enabling, the usual suspects would be reasonable choices: configuration file/registry/environment variable/loader specific proc query/compile time config.

From a developer point of view, how would one want to control such a mode?

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I agree, the loader needs to do something. I think we should log and throw an acceptable error.

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After thinking about this, I think the loader should always check. If the developer is using the loader entrypoints, then they are already in a slower path for everything but instance extensions. And in the case of instance extensions, it doesn't need to be very fast since there's already a lot of work the loader is performing (and even perhaps emulating in the case of some drivers supporting a given instance extension and others not).

My reasoning is that if the dispatch handle is wrong, we're going to be going off in la-la-land anyway. So I'll add logging to at least catch the case of bad handles before we die. I'm also planning on trying to add the VUID in the message so that if anyone ever turns on debug utils with validation, they will catch these as well.

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Added. It will abort still, but it will at least output a message on abort indicating that the handle is invalid.

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