Pad code to multiple of 32 bytes.

Changelog.md

@@ -1,6 +1,7 @@
 ### 0.5.4 (unreleased)
 
 Bugfixes:
+ * Code generator: Defensively pad allocation of creationCode and runtimeCode to multiples of 32 bytes.
  * Parser: Disallow empty import statements.
  * Type system: Properly report packed encoded size for arrays and structs (mostly unused until now).
 

libsolidity/codegen/ExpressionCompiler.cpp

@@ -1348,7 +1348,7 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 			m_context.appendInlineAssembly(
 				Whiskers(R"({
 					mstore(start, sub(end, add(start, 0x20)))
-					mstore(<free>, end)
+					mstore(<free>, and(add(end, 31), not(31)))
 				})")("free", to_string(CompilerUtils::freeMemoryPointer)).render(),
 				{"start", "end"}
 			);

test/libsolidity/SolidityEndToEndTest.cpp

@@ -14275,6 +14275,25 @@ BOOST_AUTO_TEST_CASE(code_access)
 	ABI_CHECK(codeRuntime1, codeRuntime2);
 }
 
+BOOST_AUTO_TEST_CASE(code_access_padding)
+{
+	char const* sourceCode = R"(
+		contract C {
+			function diff() public pure returns (uint remainder) {
+				bytes memory a = type(D).creationCode;
+				bytes memory b = type(D).runtimeCode;
+				assembly { remainder := mod(sub(b, a), 0x20) }
+			}
+		}
+		contract D {
+			function f() public pure returns (uint) { return 7; }
+		}
+	)";
+	compileAndRun(sourceCode, 0, "C");
+	// This checks that the allocation function pads to multiples of 32 bytes
+	ABI_CHECK(callContractFunction("diff()"), encodeArgs(0));
+}
+
 BOOST_AUTO_TEST_CASE(code_access_create)
 {
 	char const* sourceCode = R"(