fix: allow negative gas refund propagation (#333)

Author: abmcar

src/compiler/evm_frontend/evm_imported.cpp

@@ -794,6 +794,7 @@ const uint8_t *evmHandleCreateInternal(zen::runtime::EVMInstance *Instance,
   if (GasUsed != 0) {
     Instance->chargeGas(GasUsed);
   }
+  // Track subcall refund (may be negative)
   Instance->addGasRefund(Result.gas_refund);
 
   std::vector<uint8_t> ReturnData(Result.output_data,
@@ -956,6 +957,7 @@ static uint64_t evmHandleCallInternal(zen::runtime::EVMInstance *Instance,
     Instance->chargeGas(GasUsed);
   }
 
+  // Track subcall refund (may be negative)
   Instance->addGasRefund(Result.gas_refund);
 
   // Copy return data to memory if output area is specified.

src/evm/interpreter.h

@@ -30,7 +30,7 @@ struct EVMFrame {
   evmc_message Msg = {};
   evmc::Host *Host = nullptr;
   evmc_tx_context MTx = {};
-  uint64_t GasRefundSnapshot = 0;
+  int64_t GasRefundSnapshot = 0;
 
   size_t Sp = 0;
   uint64_t Pc = 0;

src/evm/opcode_handlers.cpp

@@ -1461,11 +1461,8 @@ void CallHandler::doExecute() {
     return;
   }
 
-  if (Result.gas_refund > 0) {
-    // Track subcall refund at Instance level
-    Context->getInstance()->addGasRefund(Result.gas_refund);
-  }
-
+  // Track subcall refund at Instance level (may be negative)
+  Context->getInstance()->addGasRefund(Result.gas_refund);
   Context->setStatus(EVMC_SUCCESS);
 }
 

src/runtime/evm_instance.h

@@ -59,9 +59,9 @@ class EVMInstance final : public RuntimeObject<EVMInstance> {
   void chargeGas(uint64_t GasCost);
   void addGas(uint64_t GasAmount);
 
-  void addGasRefund(uint64_t Amount) { GasRefund += Amount; }
-  void setGasRefund(uint64_t Amount) { GasRefund = Amount; }
-  uint64_t getGasRefund() const { return GasRefund; }
+  void addGasRefund(int64_t Amount) { GasRefund += Amount; }
+  void setGasRefund(int64_t Amount) { GasRefund = Amount; }
+  int64_t getGasRefund() const { return GasRefund; }
   void restoreGasRefundSnapshot() {
     if (!GasRefundStack.empty()) {
       GasRefund = GasRefundStack.back();
@@ -288,7 +288,7 @@ class EVMInstance final : public RuntimeObject<EVMInstance> {
   newEVMInstance(Isolation &Iso, const EVMModule &Mod, uint64_t GasLimit = 0);
 
   const EVMModule *Mod = nullptr;
-  uint64_t GasRefund = 0;
+  int64_t GasRefund = 0;
   // memory
   uint8_t *MemoryBase = nullptr;
   uint64_t MemorySize = 0;