Transaction: Run all computations via EVMC `execute`

1. Send all EVM executions through the EVMC `execute` function.

   It leads to the same place in the end as calling `Computation` before, but
   `execute` is the API function used by all EVMC implementations, and it is
   very explicit what data is passed back and forth.

2. As a consequence this starts using the new `host_services` code from EVM, so
   this is a significant change to the paths used for account state processing.

3. Because we will have to remove the `newComputation` call on the host side,
   anticipating that the contract code is now saved in `host` instead of being
   copied around.  As it's saved in `host`, there is no need to pass it
   separately to `evmcExecComputation`.

Signed-off-by: Jamie Lokier <jamie@shareable.org>

nimbus/transaction/call_common.nim

@@ -45,7 +45,7 @@ type
     memory*:          Memory            # EVM memory on return (for test only).
     error*:           Error             # Error if `isError` (for test only).
 
-proc hostToComputationMessage(msg: EvmcMessage): Message =
+proc hostToComputationMessage*(msg: EvmcMessage): Message =
   Message(
     kind:            CallKind(msg.kind),
     depth:           msg.depth,
@@ -162,6 +162,7 @@ proc setupHost(call: CallParams): TransactionHost =
 
     let cMsg = hostToComputationMessage(host.msg)
     host.computation = newComputation(vmState, cMsg, code)
+    shallowCopy(host.code, code)
 
   else:
     if call.input.len > 0:
@@ -176,6 +177,26 @@ proc setupHost(call: CallParams): TransactionHost =
 
   return host
 
+proc doExec(host: TransactionHost, call: CallParams) =
+  let c = host.computation
+  if call.noTransfer:
+    # TODO: This isn't doing `noTransfer` properly yet, just enough for
+    # fixtures tests.
+    executeOpcodes(c)
+    doAssert c.continuation.isNil
+    doAssert c.child.isNil
+  else:
+    execComputation(c)
+
+when defined(evmc_enabled):
+  import ./host_services
+  proc doExecEvmc(host: TransactionHost, call: CallParams) =
+    if call.noTransfer:
+      let c = host.computation
+      c.setError("Unable to perform noTransfer computations in EVMC mode", true)
+    else:
+      let callResult = evmcExecComputation(host)
+
 proc runComputation*(call: CallParams): CallResult =
   let host = setupHost(call)
   let c = host.computation
@@ -189,14 +210,10 @@ proc runComputation*(call: CallParams): CallResult =
     host.vmState.mutateStateDB:
       db.subBalance(call.sender, call.gasLimit.u256 * call.gasPrice.u256)
 
-  if call.noTransfer:
-    # TODO: This isn't doing `noTransfer` properly yet, just enough for
-    # fixtures tests.
-    executeOpcodes(c)
-    doAssert c.continuation.isNil
-    doAssert c.child.isNil
+  when defined(evmc_enabled):
+    doExecEvmc(host, call)
   else:
-    execComputation(c)
+    doExec(host, call)
 
   # Calculated gas used, taking into account refund rules.
   var gasRemaining: GasInt = 0

nimbus/transaction/evmc_host_glue.nim

@@ -90,7 +90,7 @@ proc evmc_create_nimbus_evm(): ptr evmc_vm {.cdecl, importc.}
 # a separate library yet.
 import ./evmc_vm_glue
 
-proc evmcExecComputation*(host: TransactionHost, code: seq[byte]): EvmcResult =
+proc evmcExecComputation*(host: TransactionHost): EvmcResult =
   let vm = evmc_create_nimbus_evm()
   if vm.isNil:
     echo "Warning: No EVM"
@@ -119,5 +119,5 @@ proc evmcExecComputation*(host: TransactionHost, code: seq[byte]): EvmcResult =
   {.gcsafe.}:
     vm.execute(vm, hostInterface[].addr, hostContext,
                evmc_revision(host.vmState.fork), host.msg,
-               if code.len > 0: code[0].unsafeAddr else: nil,
-               code.len.csize_t)
+               if host.code.len > 0: host.code[0].unsafeAddr else: nil,
+               host.code.len.csize_t)

nimbus/transaction/host_types.nim

@@ -55,6 +55,7 @@ type
     computation*:     Computation
     msg*:             EvmcMessage
     input*:           seq[byte]
+    code*:            seq[byte]
     cachedTxContext*: bool
     txContext*:       EvmcTxContext
     logEntries*:      seq[Log]