Consolidation for communication structs/defines

[Gregor Haas]

Hi all,

I'm working on a PR that would deduplicate the definitions of various structs and definitions across the Keystone stack. These changes could potentially be breaking (i.e. lead to merge and rebase conflicts) in your forks -- if you've implemented custom syscalls, driver extensions, SDK features, etc please read on for a quick summary.

Specifically, this PR is concerned with structs/defines which are used in inter-component communication -- that is, from between the SDK to the driver or the eapp to the runtime. Currently these are scattered around in a few places, and if you wish to implement e.g. a new Eyrie syscall, you must make sure to add your syscall number in multiple places. Instead, thisgoog_1561791967 PR would centralize these definitions in various headers under the SDK; specifically, at sdk/include/shared. Each pair of Keystone subcomponents wishing to communicate would then include a mutual header from this directory.

The PR is at https://github.com/keystone-enclave/keystone/pull/407; I welcome any questions, comments, concerns, etc! If none come up, I plan to land this sometime early next week.

Thanks,

Gregor