# Hardforks and EIPs

The hardfork is a comptime parameter. `Eips` (`src/eips_and_hardforks/eips.zig`)
turns a `Hardfork` into a concrete EIP set, and handlers query that set at
comptime, so a Berlin build contains no London code.

```zig
const Evm = @import("evm").Evm;
const eips = @import("evm").Eips;

const London = Evm(.{ .eips = eips{ .hardfork = .LONDON } });
```

## The `Hardfork` enum

Declared in `lib/voltaire/src/primitives/hardfork.zig` and re-exported as
`@import("evm").Hardfork`:

| Variant | Date | EVM-visible change |
| --- | --- | --- |
| `FRONTIER` | Jul 2015 | Base instruction set |
| `HOMESTEAD` | Mar 2016 | `DELEGATECALL` (EIP-7), EIP-2, EIP-8 |
| `DAO` | Jul 2016 | State-only; no EVM changes |
| `TANGERINE_WHISTLE` | Oct 2016 | EIP-150 gas repricing for IO-heavy ops |
| `SPURIOUS_DRAGON` | Nov 2016 | EIP-155/160/161 — replay protection, empty-account removal |
| `BYZANTIUM` | Oct 2017 | `REVERT`, `RETURNDATASIZE`, `RETURNDATACOPY`, `STATICCALL`, BN254 precompiles |
| `CONSTANTINOPLE` | Feb 2019 | `CREATE2`, `SHL`/`SHR`/`SAR`, `EXTCODEHASH`, EIP-1283 |
| `PETERSBURG` | Feb 2019 | Reverts EIP-1283 (reentrancy risk) |
| `ISTANBUL` | Dec 2019 | `CHAINID`, `SELFBALANCE`, EIP-2200, EIP-1108, EIP-152 |
| `MUIR_GLACIER` | Jan 2020 | Difficulty bomb delay only |
| `BERLIN` | Apr 2021 | EIP-2929 warm/cold gas, EIP-2930 access lists, EIP-2565 |
| `LONDON` | Aug 2021 | EIP-1559 `BASEFEE`, EIP-3529 refund reduction, EIP-3541 |
| `ARROW_GLACIER` | Dec 2021 | Difficulty bomb delay only |
| `GRAY_GLACIER` | Jun 2022 | Difficulty bomb delay only |
| `MERGE` | Sep 2022 | EIP-4399 `PREVRANDAO` replaces `DIFFICULTY` |
| `SHANGHAI` | Apr 2023 | `PUSH0` (EIP-3855), EIP-3860 initcode cap, EIP-4895 withdrawals |
| `CANCUN` | Mar 2024 | `TLOAD`/`TSTORE` (EIP-1153), `MCOPY` (EIP-5656), EIP-4844 blobs, EIP-6780, EIP-4788, EIP-7516 |
| `PRAGUE` | — | EIP-7702 delegation, EIP-2537 BLS12-381, EIP-2935, EIP-6110, EIP-7002 |
| `OSAKA` | — | EIP-7883, EIP-7823, EIP-7825, EIP-7934 |

**`CANCUN` is the default.** `build.zig` accepts a subset of these via
`-Devm-hardfork=`: `FRONTIER`, `HOMESTEAD`, `BYZANTIUM`, `BERLIN`, `LONDON`,
`SHANGHAI`, `CANCUN`. The remaining variants are reachable from Zig by naming the
config directly.

## EIP sets

`Eips.get_active_eips()` returns the exact list per fork. As of Cancun that is:

```
2, 7, 8, 100, 140, 145, 150, 152, 155, 160, 161, 196, 197, 198, 211, 214,
649, 658, 1014, 1052, 1108, 1153, 1283, 1344, 1559, 1884, 2028, 2200, 2565,
2718, 2929, 2930, 3198, 3529, 3541, 3651, 3675, 3855, 3860, 4345, 4399,
4788, 4844, 4895, 5133, 5656, 6780, 7516
```

Prague adds `2537, 2935, 3074, 6110, 7002, 7702`. Osaka adds `7883, 7823, 7825,
7934` (and drops 3074).

Query it at comptime:

```zig
const eips = @import("evm").Eips;
const cancun = eips{ .hardfork = .CANCUN };

comptime {
    // Fails to compile if EIP-1153 (TLOAD/TSTORE) is not active.
    if (!cancun.is_eip_active(1153)) @compileError("expected TSTORE");
}
```

### Overriding individual EIPs

`eip_overrides` lets you activate or deactivate one EIP independently of the fork
— useful for testnets, for L2s that diverge on a single EIP, and for bisecting a
spec-test failure to a specific EIP:

```zig
const Custom = @import("evm").Evm(.{
    .eips = eips{ .hardfork = .SHANGHAI },
    .eip_overrides = &.{
        .{ .eip = 1153, .enabled = true },   // TLOAD/TSTORE before Cancun
    },
});
```

## Precompiles

Addresses are defined in `lib/voltaire/src/precompiles/root.zig`:

| Address | Name | Since |
| --- | --- | --- |
| `0x01` | `ECRECOVER` | Frontier |
| `0x02` | `SHA256` | Frontier |
| `0x03` | `RIPEMD160` | Frontier |
| `0x04` | `IDENTITY` | Frontier |
| `0x05` | `MODEXP` | Byzantium (EIP-198) |
| `0x06` | `ECADD` (BN254) | Byzantium (EIP-196) |
| `0x07` | `ECMUL` (BN254) | Byzantium (EIP-197) |
| `0x08` | `ECPAIRING` (BN254) | Byzantium |
| `0x09` | `BLAKE2F` | Istanbul (EIP-152) |
| `0x0A` | `POINT_EVALUATION` (KZG) | Cancun (EIP-4844) |

The BN254 and BLS12-381 implementations come from the vendored arkworks Rust
crate in `lib/voltaire`; KZG comes from `c-kzg-4844` and `blst`. That is why a
build needs Cargo and a C compiler, and why dropping precompiles
(`-Dno_precompiles=true`) is the biggest single lever on binary size.

:::warning[Known weak spot]
The repository's own README reports that most Ethereum spec-test failures are
concentrated in the `ecmul`/BN254 tests. If your workload leans on `0x06`–`0x08`,
verify against another implementation before trusting results. See
[Project status](/status).
:::

### Replacing a precompile

```zig
const PrecompileOutput = struct { output: []const u8, gas_used: u64, success: bool };

const Custom = @import("evm").Evm(.{
    .precompile_overrides = &.{
        .{ .address = my_address, .execute = &myPrecompile },
    },
});
```

The `execute` signature is
`fn (allocator: std.mem.Allocator, input: []const u8, gas_limit: u64) anyerror!PrecompileOutput`.