JIT services

Revision as of 16:52, 15 April 2020 by Yellows8 (talk | contribs)

JIT is a sysmodule for run-time code generation (allowing for overlapping R-X and RW- views of memory). This was added to retail with [10.0.0+]. This was also supported in sdknso for a number of versions prior.

nnMain just initializes ro:1, then starts hosting the service from the main-thread with max_sessions=1 (threads are not created for service-hosting).

This is intended to only be used by Applications. The service-init in sdknso just uses PrepareForJit at the start, then gets the service.

sdknso CreateJitEnvironment implements the remaining initialization. After some validation, this uses svcCreateCodeMemory (can be called twice). Then #CreateJitEnvironment is used. TransferMemory with an user-specified buffer is created with permissions=None, which is then used with #LoadPlugin. When successful, this lastly uses #GetCodeAddress.

This loads the user-specified NRO into sysmodule-context ("DllPlugin"), and calls various symbols from that NRO. It seems the code writing (in cmd GenerateCode) is done via symbol-calling, allowing the NRO to handle input_buffer->code translation+writing.

jit:u

This is "nn::jitsrv::IJitService".

Cmd Name
0 #CreateJitEnvironment

CreateJitEnvironment

Takes two input u64s, 3 input handles, returns an #IJitEnvironment.

IJitEnvironment

This is "nn::jitsrv::IJitEnvironment".

Cmd Name
0 #GenerateCode
1 #Control
1000 #LoadPlugin
1001 #GetCodeAddress

GenerateCode

Takes an u32, an u64, a #CodeRange, a #CodeRange, a #Struct32, a type-0x5 input buffer, a type-0x6 output buffer, and returns an output s32, a #CodeRange, a #CodeRange.

Control

Takes an input u64, a type-0x5 input buffer, a type-0x6 output buffer, and returns an output s32.

LoadPlugin

Takes an input u64, a handle, two type-0x5 input buffers, no output.

GetCodeAddress

No input, returns two output u64s which are loaded from state.

CodeRange

This is "nn::jit::CodeRange". This is a 0x10-byte struct. This is 8-byte aligned.

Struct32

This is "nn::jitsrv::Struct32". This is a 0x20-byte struct. This is 8-byte aligned.