Implement bignum system library using intx

src/eei.cpp

@@ -845,4 +845,35 @@ void WasmEngine::collectBenchmarkingData()
     }
     return ret;
   }
+
+  intx::uint256 EthereumInterface::loadBignum256(uint32_t srcOffset)
+  {
+    uint8_t data[32];
+    loadMemory(srcOffset, data, 32);
+    // FIXME: change this to little endian?
+    return intx::be::uint256(data);
+  }
+
+  void EthereumInterface::storeBignum256(intx::uint256 const& src, uint32_t dstOffset)
+  {
+    uint8_t data[32];
+    // FIXME: change this to little endian?
+    intx::be::store(data, src);
+    storeMemory(data, dstOffset, 32);
+  }
+
+  void EthereumInterface::mul256(uint32_t aOffset, uint32_t bOffset, uint32_t retOffset)
+  {
+    storeBignum256(loadBignum256(aOffset) * loadBignum256(bOffset), retOffset);
+  }
+
+  void EthereumInterface::umulmod256(uint32_t aOffset, uint32_t bOffset, uint32_t modOffset, uint32_t retOffset)
+  {
+    using intx::uint512;
+    auto a = loadBignum256(aOffset);
+    auto b = loadBignum256(bOffset);
+    auto mod = loadBignum256(modOffset);
+    auto ret = mod != 0 ? ((uint512{a} * uint512{b}) % uint512{mod}).lo : 0;
+    storeBignum256(ret, retOffset);
+  }
 }

src/eei.h

@@ -23,6 +23,8 @@
 #include <evmc/evmc.h>
 #include <evmc/evmc.hpp>
 
+#include <intx/intx.hpp>
+
 #include "exceptions.h"
 #include "helpers.h"
 
@@ -163,6 +165,10 @@ class EthereumInterface {
   uint32_t eeiCreate(uint32_t valueOffset, uint32_t dataOffset, uint32_t length, uint32_t resultOffset);
   void eeiSelfDestruct(uint32_t addressOffset);
 
+  // Bignum system library
+  void mul256(uint32_t aOffset, uint32_t bOffset, uint32_t retOffset);
+  void umulmod256(uint32_t aOffset, uint32_t bOffset, uint32_t modOffset, uint32_t retOffset);
+
 private:
   void eeiRevertOrFinish(bool revert, uint32_t offset, uint32_t size);
 
@@ -191,6 +197,9 @@ class EthereumInterface {
   evmc_uint256be loadUint128(uint32_t srcOffset);
   void storeUint128(evmc_uint256be const& src, uint32_t dstOffset);
 
+  intx::uint256 loadBignum256(uint32_t srcOffset);
+  void storeBignum256(intx::uint256 const& src, uint32_t dstOffset);
+
   inline int64_t maxCallGas(int64_t gas) { return gas - (gas / 64); }
 
   /* Checks for overflow and safely charges gas for variable length data copies */

src/wabt.cpp

@@ -584,6 +584,39 @@ ExecutionResult WabtEngine::execute(
     }
   );
 
+  // Create the bignum host module
+  // The lifecycle of this pointer is handled by `env`.
+  hostModule = env.AppendHostModule("bignum");
+  heraAssert(hostModule, "Failed to create host module.");
+
+  hostModule->AppendFuncExport(
+    "mul256",
+    {{Type::I32, Type::I32, Type::I32}, {}},
+    [&interface](
+      const interp::HostFunc*,
+      const interp::FuncSignature*,
+      const interp::TypedValues& args,
+      interp::TypedValues&
+    ) {
+      interface.mul256(args[0].value.i32, args[1].value.i32, args[2].value.i32);
+      return interp::Result::Ok;
+    }
+  );
+
+  hostModule->AppendFuncExport(
+    "umulmod256",
+    {{Type::I32, Type::I32, Type::I32, Type::I32}, {}},
+    [&interface](
+      const interp::HostFunc*,
+      const interp::FuncSignature*,
+      const interp::TypedValues& args,
+      interp::TypedValues&
+    ) {
+      interface.umulmod256(args[0].value.i32, args[1].value.i32, args[2].value.i32, args[3].value.i32);
+      return interp::Result::Ok;
+    }
+  );
+
 #if HERA_DEBUGGING
   // Create debug host module
   // The lifecycle of this pointer is handled by `env`.
@@ -1112,6 +1145,37 @@ void WabtEngine::verifyContract(bytes_view code) {
     }
   );
 
+  // Create the bignum host module
+  // The lifecycle of this pointer is handled by `env`.
+  hostModule = env.AppendHostModule("bignum");
+  heraAssert(hostModule, "Failed to create host module.");
+
+  hostModule->AppendFuncExport(
+    "mul256",
+    {{Type::I32, Type::I32, Type::I32}, {}},
+    [&](
+      const interp::HostFunc*,
+      const interp::FuncSignature*,
+      const interp::TypedValues&,
+      interp::TypedValues&
+    ) {
+      return interp::Result::Ok;
+    }
+  );
+
+  hostModule->AppendFuncExport(
+    "umulmod256",
+    {{Type::I32, Type::I32, Type::I32, Type::I32}, {}},
+    [&](
+      const interp::HostFunc*,
+      const interp::FuncSignature*,
+      const interp::TypedValues&,
+      interp::TypedValues&
+    ) {
+      return interp::Result::Ok;
+    }
+  );
+
 #if HERA_DEBUGGING
   // Create debug host module
   // The lifecycle of this pointer is handled by `env`.

src/wavm.cpp

@@ -249,6 +249,20 @@ namespace wavm_host_module {
     interface.top()->eeiSelfDestruct(addressOffset);
   }
 
+  // the host module is called 'bignum'
+  DEFINE_INTRINSIC_MODULE(bignum)
+
+  // host functions follow
+  DEFINE_INTRINSIC_FUNCTION(bignum, "mul256", void, mul256, U32 a, U32 b, U32 ret)
+  {
+    interface.top()->mul256(a, b, ret);
+  }
+
+  DEFINE_INTRINSIC_FUNCTION(bignum, "umulmod256", void, umulmod246, U32 a, U32 b, U32 mod, U32 ret)
+  {
+    interface.top()->umulmod256(a, b, mod, ret);
+  }
+
   // this is needed for resolving names of imported host functions
   struct HeraWavmResolver : Runtime::Resolver {
     HashMap<string, Runtime::ModuleInstance*> moduleNameToInstanceMap;
@@ -349,10 +363,14 @@ ExecutionResult WavmEngine::internalExecute(
   Runtime::GCPointer<Runtime::ModuleInstance> ethereumHostModule = Intrinsics::instantiateModule(compartment, wavm_host_module::INTRINSIC_MODULE_REF(ethereum), "ethereum", {});
   heraAssert(ethereumHostModule, "Failed to create host module.");
 
+  Runtime::GCPointer<Runtime::ModuleInstance> bignumHostModule = Intrinsics::instantiateModule(compartment, wavm_host_module::INTRINSIC_MODULE_REF(bignum), "bignum", {});
+  heraAssert(bignumHostModule, "Failed to create host module.");
+
   // prepare contract module to resolve links against host module
   wavm_host_module::HeraWavmResolver resolver;
   // TODO: move this into the constructor?
   resolver.moduleNameToInstanceMap.set("ethereum", ethereumHostModule);
+  resolver.moduleNameToInstanceMap.set("bignum", bignumHostModule);
   Runtime::LinkResult linkResult = Runtime::linkModule(moduleIR, resolver);
   ensureCondition(linkResult.success, ContractValidationFailure, "Couldn't link contract against host module.");
 
@@ -457,7 +475,7 @@ void WavmEngine::verifyContract(bytes_view code)
 
   for (auto const& import: moduleIR.functions.imports) {
 #if HERA_DEBUGGING
-    if (import.moduleName == "debug")
+    if (import.moduleName == "debug" || import.moduleName == "bignum")
       continue;
 #endif