| 438fc938 | 25-Nov-2024 |
Alex Crichton <[email protected]> |
pulley: Implement interpreter-to-host calls (#9665)
* pulley: Implement interpreter-to-host calls
This commit is an initial stab at implementing interpreter-to-host
communication in Pulley. The bas
pulley: Implement interpreter-to-host calls (#9665)
* pulley: Implement interpreter-to-host calls
This commit is an initial stab at implementing interpreter-to-host
communication in Pulley. The basic problem is that Pulley needs the
ability to call back into Wasmtime to implement tasks such as
`memory.grow`, imported functions, etc. For native platforms this is a
simple `call_indirect` operation in Cranelift but the story for Pulley
must be different because it's effectively switching from interpreted
code to native code.
The initial idea for this in #9651 is replaced here and looks mostly
similar but with a few changes. The overall structure of how this works
is:
* A new `call_indirect_host` opcode is added to Pulley.
* Function signatures that can be called from Pulley bytecode are
statically enumerated at build-time.
* This enables the implementation of `call_indirect_host` to take an
immediate of which signature is being used and cast the function
pointer to the right type.
* A new pulley-specific relocation is added to Cranelift for this opcode.
* `RelocDistance::Far` calls to a name trigger the use of
`call_indirect_host`.
* The relocation is filled in by Wasmtime after compilation where the
signature number is inserted.
* A new `NS_*` value for user-function namespaces is reserved in
`wasmtime-cranelift` for this new namespace of functions.
* Code generation for Pulley in `wasmtime-cranelift` now has
Pulley-specific handling of the wasm-to-host transition where all
previous `call_indirect` instructions are replaced with a call to a
"backend intrinsic" which gets lowered to a `call_indirect_host`.
Note that most of this still isn't hooked up everywhere in Wasmtime.
That means that the testing here is pretty light at this time. It'll
require a fair bit more work to get everything fully integrated from
Wasmtime in Pulley. This is expected to be one of the significant
remaining chunks of work and should help unblock future testing (or make
those diffs smaller ideally).
* Review comments
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