Added system call tracing when performing ProcessBeaconBlockRoot

Added a `start/end` system where tracer can be notified that processing of some Ethereum system calls is starting processing and also notifies it when the processing has completed.

Doing a `start/end` for system call will enable tracers to "route" incoming next tracing events to go to a separate bucket than other EVM calls. Those not interested by this fact can simply avoid registering the hooks.

The EVM call is going to be traced normally afterward between the signals provided by those 2 new hooks but outside of a transaction context `OnTxStart/End`. That something implementors of live tracers will need to be aware of (since only "trx tracers" are not concerned by `ProcessBeaconRoot`).

One thing of importance for tracers

core/state_processor.go

@@ -186,6 +186,13 @@ func ApplyTransaction(config *params.ChainConfig, bc ChainContext, author *commo
 // ProcessBeaconBlockRoot applies the EIP-4788 system call to the beacon block root
 // contract. This method is exported to be used in tests.
 func ProcessBeaconBlockRoot(beaconRoot common.Hash, vmenv *vm.EVM, statedb *state.StateDB) {
+	if vmenv.Config.Tracer != nil && vmenv.Config.Tracer.OnSystemCallStart != nil {
+		vmenv.Config.Tracer.OnSystemCallStart()
+	}
+	if vmenv.Config.Tracer != nil && vmenv.Config.Tracer.OnSystemCallEnd != nil {
+		defer vmenv.Config.Tracer.OnSystemCallEnd()
+	}
+
 	// If EIP-4788 is enabled, we need to invoke the beaconroot storage contract with
 	// the new root
 	msg := &Message{

core/tracing/hooks.go

@@ -81,6 +81,10 @@ type (
 	TxEndHook = func(receipt *types.Receipt, err error)
 
 	// EnterHook is invoked when the processing of a message starts.
+	//
+	// Take note that EnterHook, when in the context of a live tracer, can be invoked
+	// outside of the `OnTxStart` and `OnTxEnd` hooks when dealing with system calls,
+	// see [OnSystemCallStartHook] and [OnSystemCallEndHook] for more information.
 	EnterHook = func(depth int, typ byte, from common.Address, to common.Address, input []byte, gas uint64, value *big.Int)
 
 	// ExitHook is invoked when the processing of a message ends.
@@ -89,6 +93,10 @@ type (
 	// ran out of gas when attempting to persist the code to database did not
 	// count as a call failure and did not cause a revert of the call. This will
 	// be indicated by `reverted == false` and `err == ErrCodeStoreOutOfGas`.
+	//
+	// Take note that ExitHook, when in the context of a live tracer, can be invoked
+	// outside of the `OnTxStart` and `OnTxEnd` hooks when dealing with system calls,
+	// see [OnSystemCallStartHook] and [OnSystemCallEndHook] for more information.
 	ExitHook = func(depth int, output []byte, gasUsed uint64, err error, reverted bool)
 
 	// OpcodeHook is invoked just prior to the execution of an opcode.
@@ -125,6 +133,22 @@ type (
 	// GenesisBlockHook is called when the genesis block is being processed.
 	GenesisBlockHook = func(genesis *types.Block, alloc types.GenesisAlloc)
 
+	// OnSystemCallStartHook is called when a system call is about to be executed. Today,
+	// this hook is invoked when the EIP-4788 system call is about to be executed to set the
+	// beacon block root.
+	//
+	// After this hook, the EVM call tracing will happened as usual so you will receive a `OnEnter/OnExit`
+	// as well as state hooks between this hook and the `OnSystemCallEndHook`.
+	//
+	// Note that system call happens outside normal transaction execution, so the `OnTxStart/OnTxEnd` hooks
+	// will not be invoked.
+	OnSystemCallStartHook = func()
+
+	// OnSystemCallEndHook is called when a system call has finished executing. Today,
+	// this hook is invoked when the EIP-4788 system call is about to be executed to set the
+	// beacon block root.
+	OnSystemCallEndHook = func()
+
 	/*
 		- State events -
 	*/
@@ -155,12 +179,14 @@ type Hooks struct {
 	OnFault     FaultHook
 	OnGasChange GasChangeHook
 	// Chain events
-	OnBlockchainInit BlockchainInitHook
-	OnClose          CloseHook
-	OnBlockStart     BlockStartHook
-	OnBlockEnd       BlockEndHook
-	OnSkippedBlock   SkippedBlockHook
-	OnGenesisBlock   GenesisBlockHook
+	OnBlockchainInit  BlockchainInitHook
+	OnClose           CloseHook
+	OnBlockStart      BlockStartHook
+	OnBlockEnd        BlockEndHook
+	OnSkippedBlock    SkippedBlockHook
+	OnGenesisBlock    GenesisBlockHook
+	OnSystemCallStart OnSystemCallStartHook
+	OnSystemCallEnd   OnSystemCallEndHook
 	// State events
 	OnBalanceChange BalanceChangeHook
 	OnNonceChange   NonceChangeHook