Implement CODESIZE and CODECOPY

Author: sz-piotr

packages/evm/src/Memory.ts

@@ -15,7 +15,7 @@ export class Memory {
   }
 
   getBytes (offset: number, length: number) {
-    this.onMemoryAccess(offset, length)
+    this.useGasForAccess(offset, length)
     if (length === 0) {
       return []
     }
@@ -24,7 +24,7 @@ export class Memory {
   }
 
   setBytes (offset: number, bytes: Byte[]) {
-    this.onMemoryAccess(offset, bytes.length)
+    this.useGasForAccess(offset, bytes.length)
     if (bytes.length === 0) {
       return
     }
@@ -34,7 +34,7 @@ export class Memory {
     }
   }
 
-  private onMemoryAccess (offset: number, length: number) {
+  useGasForAccess (offset: number, length: number) {
     if (length === 0) {
       return
     }

packages/evm/src/opcodes/code.ts

@@ -0,0 +1,25 @@
+import { ExecutionContext } from '../ExecutionContext'
+import { GasCost } from './gasCosts'
+import { Bytes32 } from '../Bytes32'
+import { Byte } from '../Byte'
+
+export function opCODESIZE (ctx: ExecutionContext) {
+  ctx.useGas(GasCost.BASE)
+  ctx.stack.push(Bytes32.fromNumber(ctx.message.code.length))
+}
+
+export function opCODECOPY (ctx: ExecutionContext) {
+  const memoryOffset = ctx.stack.pop().toUnsignedNumber()
+  const codeOffset = ctx.stack.pop().toUnsignedNumber()
+  const memorySize = ctx.stack.pop().toUnsignedNumber()
+
+  ctx.useGas(GasCost.VERYLOW + GasCost.COPY * Math.ceil(memorySize / 32))
+  // we subtract the gas early in case of OutOfGas
+  ctx.memory.useGasForAccess(memoryOffset, memorySize)
+
+  const code = ctx.message.code.slice(codeOffset, codeOffset + memorySize)
+  while (code.length < memorySize) {
+    code.push(0x00 as Byte)
+  }
+  ctx.memory.setBytes(memoryOffset, code)
+}

packages/evm/src/opcodes/gasCosts.ts

@@ -2,6 +2,7 @@ export const GasCost = {
   ZERO: 0,
   BASE: 2,
   VERYLOW: 3,
+  COPY: 3,
   LOW: 5,
   MID: 8,
   HIGH: 10,

packages/evm/src/opcodes/index.ts

@@ -39,6 +39,7 @@ import { makeOpDUP, makeOpSWAP, opPOP } from './stack'
 import { opMSIZE, opMLOAD, opMSTORE, opMSTORE8 } from './memory'
 import { opSSTORE, opSLOAD } from './storage'
 import { Byte } from '../Byte'
+import { opCODESIZE, opCODECOPY } from './code'
 
 export { opUnreachable } from './invalid'
 export { makeOpPUSH } from './stack'
@@ -76,6 +77,8 @@ const OP_CODES: Record<number, Opcode | undefined> = {
   0x1b: opSHL,
   0x1c: opSHR,
   0x1d: opSAR,
+  0x38: opCODESIZE,
+  0x39: opCODECOPY,
   0x50: opPOP,
   0x51: opMLOAD,
   0x52: opMSTORE,

packages/evm/test/helpers/executeAssembly.ts

@@ -29,7 +29,7 @@ export function executeAssembly (
   return executeCode({ ...DEFAULT_MESSAGE, ...params, code }, state)
 }
 
-function assemblyToBytecode (code: string): Byte[] {
+export function assemblyToBytecode (code: string): Byte[] {
   const instructions = code.trim().split(/\s+/)
   const result: Byte[] = []
   for (const instruction of instructions) {

packages/evm/test/opcodes/code.test.ts

@@ -0,0 +1,57 @@
+import {
+  expectStorage,
+  Int256,
+  expectGas,
+  expectReturn,
+  assemblyToBytecode,
+  memoryGas,
+  expectUnderflow,
+} from '../helpers'
+import { GasCost } from '../../src/opcodes'
+
+describe('CODESIZE opcode', () => {
+  it('returns the code size of the current environment', () => {
+    expectStorage('CODESIZE PUSH1 00 SSTORE', {
+      [Int256.of(0)]: Int256.of(4),
+    })
+  })
+
+  it(`costs ${GasCost.BASE} gas`, () => {
+    expectGas('CODESIZE', GasCost.BASE)
+  })
+})
+
+describe('CODECOPY opcode', () => {
+  it('copies the code to the memory', () => {
+    const assembly = `
+      PUSH1 0C
+      PUSH1 00
+      PUSH1 42
+      CODECOPY
+      PUSH1 0C
+      PUSH1 42
+      RETURN
+    `
+    expectReturn(assembly, assemblyToBytecode(assembly))
+  })
+
+  it('uses a formula to calculate gas cost', () => {
+    const assembly = `
+      PUSH1 42
+      PUSH1 00
+      PUSH1 69
+      CODECOPY
+    `
+    const gas = (
+      GasCost.VERYLOW * 3 +
+      GasCost.VERYLOW +
+      GasCost.COPY * Math.ceil(0x42 / 32) +
+      memoryGas(0x69 + 0x42)
+    )
+    expectGas(assembly, gas)
+  })
+
+  it('can cause stack underflow', () => {
+    expectUnderflow('CODECOPY', 3)
+  })
+})