I was curious so I took a look: It seems they're implementing a new system; there are shared libraries in /vendor/lib/hw on my Pixel running O that aren't there on my Pixel XL running 7.1.

  sailfish:/ $ ls /vendor/lib/hw                                                                                                                   
  [email protected]        [email protected]  [email protected]  
  [email protected]               [email protected]    [email protected]        
  [email protected]                [email protected]          flp.default.so                         
  [email protected]     [email protected]              gatekeeper.msm8996.so                  
  [email protected]         [email protected]           keystore.msm8996.so                    
  [email protected]          [email protected]                sensors.vl530l0.tof.so                 
  [email protected]                 [email protected]              sound_trigger.primary.msm8996.so       
  [email protected]          [email protected]            vulkan.msm8996.so                      
  [email protected]                [email protected]       
  [email protected]  [email protected]

You can see some development in the AOSP repos (follow https://r.android.com) that supports this. For example, libhwbinder (https://android.googlesource.com/platform/system/libhwbinder...) looks to be an interface for talking with a /dev/hwbinder device, and the kernel seems to have been updated recently to support multiple Binder device instances. HAL interfaces are defined in HIDL, which looks to be implemented here: https://android.googlesource.com/platform/system/libhidl/+/m... (along with a separate hidl tool in another repo).