Add missing 63/64 rule documentation and a test (#462)

- Prominently point out the important differences of the `pallet-revive`
runtime.
- Add a test case illustrating the problem.

See also: https://github.com/paritytech/contract-issues/issues/257

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

book/src/user_guide/differences.md

@@ -18,6 +18,10 @@ Therefore, in EVM terminology, the deploy code equals the runtime code.
 
 We are aware of the following differences in the translation of Solidity code.
 
+### The `63/64` gas rule
+
+`pallet-revive` **doesn't apply the `63/64` gas rule**. We strongly advice to change any code calling untrusted contracts to supply a limited amount of gas only!
+
 ### `address.creationCode`
 
 This returns the bytecode keccak256 hash instead.
@@ -28,7 +32,7 @@ The below list contains noteworthy differences in the translation of YUL functio
 
 > [!NOTE]
 >
-> Many functions receive memory buffer offset pointer or size arguments. Since the PVM pointer size is 32 bit, supplying memory offset or buffer size values above `2^32-1` will trap the contract immediately.
+> Many functions receive memory buffer offset pointer or size arguments. The PVM pointer size is 32 bit, supplying memory offset or buffer size values above `2^32-1` may lead to `OutOfGas` errors trap contract execution.
 
 The `solc` compiler ought to always emit valid memory references, so Solidity dApp authors don't need to worry about this unless they deal with low level `assembly` code.
 
@@ -43,6 +47,10 @@ In general, revive preserves the memory layout, meaning low level memory operati
 
 In the constructor code, the offset is ignored and this always returns `0`.
 
+> [!WARNING]
+>
+> `pallet-revive` restricts the calldata size (to 128kb at the time of writing).
+
 ### `codecopy`
 
 Only supported in constructor code.
@@ -70,6 +78,10 @@ Returns the contract hash.
 
 Returns the contract hash size (constant value of `32`).
 
+### `revert`, `return`
+
+`pallet-revive` restricts the returndata size (to 128kb at the time of writing).
+
 ### `prevrandao`, `difficulty`
 
 Translates to a constant value of `2500000000000000`.

book/src/welcome.md

@@ -2,6 +2,18 @@
 
 Hello and a warm welcome to the `revive` Solidity compiler book!
 
+> [!WARNING]
+>
+> Solidity on PVM is running on the `pallet-revive` runtime. This introduces **observable semantic differences** in comparison with the EVM.
+> 
+> Study the [differences](https://paritytech.github.io/revive/user_guide/differences.html) section carefully. **Ignoring these differences may lead to defunct contracts.**
+> 
+> Notable examples:
+> - The 63/64 gas rule isn't implemented in the pallet (introduces potential DoS vector when calling other contracts)
+> - Contract instantiation works differently (by hash instead of by code)
+> - The gas model implemented by `pallet-revive` differs from Ethereum 
+> - The heap size is fixed instead of gas-metered and there's a fixed amount of stack size (contracts working fine on EVM may trap on PVM)
+
 ## Target audience
 
 - **Solidity dApp developers** should read the [user guide](./user_guide.md). Solidity on PolkaVM introduces important differences to EVM which should be well understood.