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.