ZkSync Compilation error

[wasim007choudhary]

❗ EXTCODECOPY Error When Compiling with forge build --zksync

🧩 Problem

When attempting to compile using:

forge build --zksync

the build fails with the following error:

Error
LLVM IR generator: 3731:17 The `EXTCODECOPY` instruction is not supported

However:

forge build

(compiling with standard solc) works fine — even after switching to foundryup-zksync.

But this is not useful because we specifically need compilation targeting zkSync EraVM, which requires --zksync.

---

🔍 Root Cause

The failure occurs because:

• forge build --zksync switches to zksolc

• zksolc targets EraVM

• EraVM does not support certain EVM opcodes, including:

  • EXTCODECOPY
  • Certain EXTCODESIZE patterns
  • Some low-level assembly behaviors

In this case, the issue originates from the ERC-4337 EntryPoint.sol dependency, specifically this modifier:

modifier nonReentrant() {
    require(
        tx.origin == msg.sender && msg.sender.code.length == 0,
        Reentrancy()
    );
    _;
}

The expression:

msg.sender.code.length

compiles into EVM instructions that rely on unsupported opcode behavior in EraVM.

So even though EXTCODECOPY is not explicitly written in the source code, it is generated internally during compilation.

---

🧠 Important Clarification

This error:

• ❌ Is not caused by viaIR settings
• ❌ Is not fixed by enabling optimizer
• ❌ Is not a Foundry configuration issue

It is an architectural incompatibility between:

System	Model
ERC-4337	Application-layer AA (EntryPoint-based)
zkSync Era	Protocol-native AA (Bootloader-based)

These systems are fundamentally different and cannot share the same dependency graph under --zksync.

---

⚠️ Why forge build Works

forge build

uses standard solc targeting EVM.

EVM supports EXTCODECOPY.

But this does not verify compatibility with zkSync Era.

---

✅ Correct Workaround (Clean Solution)

The proper fix is to separate projects entirely.(But will be too much of a hustle at the moment)

Recommended Structure

root/
│
├── erc4337/
│   ├── foundry.toml
│   ├── src/
│   ├── script/
│   └── lib/
│
└── zk-native/
    ├── foundry.toml
    ├── src/
    ├── script/
    └── lib/

Then compile independently:

cd erc4337
forge build

cd zk-native
forge build --zksync

This ensures:

• ERC-4337 compiles under EVM
• zk-native compiles under EraVM
• No incompatible libraries get compiled together

---

🏁 Conclusion

There is no compiler flag workaround for this issue.

The only correct architectural solution is:

🔥 Separate ERC-4337 and zk-native AA into distinct Foundry projects.

Attempting to compile ERC-4337 EntryPoint under zkSync’s EraVM will always fail due to unsupported opcodes.

---

If anyone has found a cleaner dependency-isolation strategy within a single monorepo, I’d be interested in hearing about it.

[EngrPips]

@PatrickAlphaC, your insight will be appreciated, sir.

[wasim007choudhary]

@EngrPips @PatrickAlphaC It turns out the issue had nothing to do with my folder structure or Foundry config. I was using a newer version of account-abstraction mainy in EntryPoint.sol that includes recent updates like EIP-7702 support and some internal refactoring . Those changes caused the compiler to generate low-level instructions that zkSync’s zksolc doesn’t currently handle properly, which is why I kept hitting the EXTCODECOPY error.

After downgrading to the older commit 7af70c8, the same one used in the Cyfrin repo, everything compiled without any issues. So in my case, it was simply a version compatibility mismatch between account-abstraction and zksolc.

If you want to stay on the newer version of account-abstraction, the more practical approach is to separate environments. For example, keep one setup (or folder) that uses the newer AA version with standard solc, and maintain a separate zkSync-specific setup with pinned, compatible dependencies for --zksync both having their separate foundry.toml and thus avoiding EntryPoint.sol compilation clash. That way we avoid forcing one compiler to work with a dependency version it doesn’t fully support.

[EngrPips]

I am glad you figured it out. Keep crushing it.