Implement EIP-2046 in LegacyVM

Reduced gas cost for static calls made to precompiles.
ethereum · Jul 25, 2019 · f2d070e · f2d070e
1 parent 5bf79e5
commit f2d070e
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Showing 3 changed files with 14 additions and 3 deletions.
diff --git a/libethcore/EVMSchedule.h b/libethcore/EVMSchedule.h
@@ -58,6 +58,7 @@ struct EVMSchedule
     unsigned logTopicGas = 375;
     unsigned createGas = 32000;
     unsigned callGas = 40;
+    unsigned precompileStaticCallGas = 700;
     unsigned callStipend = 2300;
     unsigned callValueTransferGas = 9000;
     unsigned callNewAccountGas = 25000;
@@ -151,6 +152,7 @@ static const EVMSchedule IstanbulSchedule = [] {
     EVMSchedule schedule = ConstantinopleFixSchedule;
     schedule.accountVersion = 1;
     schedule.txDataNonZeroGas = 16;
+    schedule.precompileStaticCallGas = 40;
     return schedule;
 }();
 

diff --git a/libevm/LegacyVMCalls.cpp b/libevm/LegacyVMCalls.cpp
@@ -204,13 +204,16 @@ bool LegacyVM::caseCallSetup(CallParameters *callParams, bytesRef& o_output)
     assert(callParams->valueTransfer == 0);
     assert(callParams->apparentValue == 0);
 
-    m_runGas = toInt63(m_schedule->callGas);
-
     callParams->staticCall = (m_OP == Instruction::STATICCALL || m_ext->staticCall);
+    Address const destinationAddr = asAddress(m_SP[1]);
+
+    if (callParams->staticCall && isPrecompiledContract(destinationAddr))
+        m_runGas = toInt63(m_schedule->precompileStaticCallGas);
+    else
+        m_runGas = toInt63(m_schedule->callGas);
 
     bool const haveValueArg = m_OP == Instruction::CALL || m_OP == Instruction::CALLCODE;
 
-    Address destinationAddr = asAddress(m_SP[1]);
     if (m_OP == Instruction::CALL &&
         (m_SP[2] > 0 || m_schedule->zeroValueTransferChargesNewAccountGas()) &&
         !m_ext->exists(destinationAddr))

diff --git a/libevm/VMFace.h b/libevm/VMFace.h
@@ -87,5 +87,11 @@ inline u256 fromAddress(Address _a)
 	return (u160)_a;
 }
 
+// Checks whether address is in the address range for precompiles according to EIP-1352
+inline bool isPrecompiledContract(Address const& _addr) noexcept
+{
+    static Address const c_maxPrecompiledAddress{0xffff};
+    return _addr <= c_maxPrecompiledAddress;
+}
 }
 }