Merge pull request #5222 from ethereum-optimism/qbzzt/230321-predeploy

feat(docs/op-stack): Show how to modify predeploys

docs/op-stack/src/.vuepress/config.js

@@ -166,6 +166,7 @@ module.exports = {
                 children: [
                   "/docs/build/tutorials/add-attr.md",
                   "/docs/build/tutorials/new-precomp.md",
+                  "/docs/build/tutorials/predeploys.md"
                 ]
               }  // End of tutorials
             ],

docs/op-stack/src/docs/build/tutorials/predeploys.md

+---
+title: Modifying Predeployed Contracts
+lang: en-US
+---
+
+::: warning 🚧 OP Stack Hacks are explicitly things that you can do with the OP Stack that are *not* currently intended for production use
+
+OP Stack Hacks are not for the faint of heart. You will not be able to receive significant developer support for OP Stack Hacks — be prepared to get your hands dirty and to work without support.
+
+:::
+
+
+OP Stack blockchains have a number of [predeployed contracts](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/src/constants.ts) that provide important functionality. 
+Most of those contracts are proxies that can be upgraded using the `proxyAdminOwner` which was configured when the network was initially deployed.
+
+The predeploys are controlled from a predeploy called [`ProxyAdmin`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/contracts/universal/ProxyAdmin.sol), whose address is `0x4200000000000000000000000000000000000018`. 
+The function to call is [`upgrade(address,address)`](https://github.com/ethereum-optimism/optimism/blob/develop/packages/contracts-bedrock/contracts/universal/ProxyAdmin.sol#L211-L229).
+The first parameter is the proxy to upgrade, and the second is the address of a new implementation.
+
+For example, the legacy `L1BlockNumber` contract is at `0x420...013`. 
+To disable this function, we'll set the implementation to `0x00...00`.
+We do this using the [Foundry](https://book.getfoundry.sh/) command `cast`.
+
+1. We'll need several constants.
+
+    - Set these addresses as variables in your terminal.
+
+        ```sh
+        L1BLOCKNUM=0x4200000000000000000000000000000000000013
+        PROXY_ADMIN=0x4200000000000000000000000000000000000018
+        ZERO_ADDR=0x0000000000000000000000000000000000000000
+        ```
+
+    - Set `PRIVKEY` to the private key of your ADMIN account.
+
+    - Set `ETH_RPC_URL`. If you're on the computer that runs the blockchain, use this command.
+
+        ```sh
+        export ETH_RPC_URL=http://localhost:8545
+        ```
+
+1. Verify `L1BlockNumber` works correctly.
+   See that when you call the contract you get a block number, and twelve seconds later you get the next one (block time on L1 is twelve seconds).
+
+   ```sh
+   cast call $L1BLOCKNUM 'number()' | cast --to-dec
+   sleep 12 && cast call $L1BLOCKNUM 'number()' | cast --to-dec
+   ```
+
+1. Get the current implementation for the contract.
+
+   ```sh
+   L1BLOCKNUM_IMPLEMENTATION=`cast call $L1BLOCKNUM "implementation()" | sed 's/000000000000000000000000//'`
+   echo $L1BLOCKNUM_IMPLEMENTATION 
+   ```
+
+1. Change the implementation to the zero address   
+
+   ```sh
+   cast send --private-key $PRIVKEY $PROXY_ADMIN "upgrade(address,address)" $L1BLOCKNUM $ZERO_ADDR
+   ```
+
+1. See that the implementation is address zero, and that calling it fails.
+
+   ```sh
+   cast call $L1BLOCKNUM 'implementation()'
+   cast call $L1BLOCKNUM 'number()'
+   ```
+
+1. Fix the predeploy by returning it to the previous implementation, and verify it works. 
+
+
+   ```sh
+   cast send --private-key $PRIVKEY $PROXY_ADMIN "upgrade(address,address)" $L1BLOCKNUM $L1BLOCKNUM_IMPLEMENTATION
+   cast call $L1BLOCKNUM 'number()' | cast --to-dec
+   ```
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