Add initial support for pluggable syscalls (#1922)

See: #1787

This PR adds initial support for pluggable syscall by allowing us to extend the default kernel and add new custom syscalls through a new kernel.

The implementation does this by moving the global bind_syscall function into kernel via a SyscallHandler trait where each kernel needs to add their new syscalls.

The implementation uses Ambassador crate which automatically create stubs for delegating kernel implementations we are not overriding in new kernels, minimizing the code we need to write.

fvm/Cargo.toml

@@ -41,6 +41,7 @@ minstant = "0.1.2"
 blake2b_simd = "1.0.0"
 byteorder = "1.4.3"
 static_assertions = "1.1.0"
+ambassador = "0.3.5"
 
 [dev-dependencies]
 pretty_assertions = "1.3.0"

fvm/src/engine/mod.rs

@@ -27,8 +27,7 @@ use crate::machine::limiter::MemoryLimiter;
 use crate::machine::{Machine, NetworkConfig};
 use crate::syscalls::error::Abort;
 use crate::syscalls::{
-    bind_syscalls, charge_for_exec, charge_for_init, record_init_time, update_gas_available,
-    InvocationData,
+    charge_for_exec, charge_for_init, record_init_time, update_gas_available, InvocationData,
 };
 use crate::Kernel;
 
@@ -514,10 +513,15 @@ impl Engine {
                 .expect("invalid instance cache entry"),
             Vacant(e) => &mut *e
                 .insert({
-                    let mut linker: Linker<InvocationData<K>> = Linker::new(&self.inner.engine);
+                    let mut linker = Linker::new(&self.inner.engine);
                     linker.allow_shadowing(true);
 
-                    bind_syscalls(&mut linker).map_err(Abort::Fatal)?;
+                    store
+                        .data()
+                        .kernel
+                        .bind_syscalls(&mut linker)
+                        .map_err(Abort::Fatal)?;
+
                     Box::new(Cache { linker })
                 })
                 .downcast_mut()

fvm/src/gas/price_list.rs

@@ -901,7 +901,6 @@ impl PriceList {
     }
 
     /// Returns the gas required for installing an actor.
-    #[cfg(feature = "m2-native")]
     pub fn on_install_actor(&self, wasm_size: usize) -> GasCharge {
         GasCharge::new(
             "OnInstallActor",