Add an extra note about EEI imports and disallowing a start function #114
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contract_interface.md
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| @@ -24,6 +25,8 @@ On successful execution, the code should return via a normal code path. | |||
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| If it needs to abort due to a failure, an *unreachable* instruction should be executed. | |||
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| Further more, the ewasm spec disallows the use of a 'start' function in an ewasm contract, because it is executed upon module instantiation. | |||
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In pwasm we decided to leave it as is. The reason for that we don't want to introduce unnecessary complication s since start function might still be used by the wasm producer. On the other hand, the logic is pretty much the same, consider this pseudo-code:
// let's say `env` is a EEI analog
try {
// this will implicitly run the `start` function
instance = instantiate_module(module, env)
instance.invoke(env, "entrypoint")
} catch {
// ...
}
there is almost no difference between running or not running the start function.
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Our decision to remove the start function was based on some detail that came up in implementing ewasm-kernel that required something to be done between instantiation and execution. @axic can elaborate a bit more on this.
I think that it seems to be a bit of a workaround that should be streamlined, so it may be revisited in the future.
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@pepyakin meanwhile I am working on a tool that checks the ECI properties (and later amends them) using the parity-wasm library. It is located at jakelang/libecic. If you have time, could you take a look and give some comments about what could be done better? I am somewhat new to Rust :)
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because it is executed upon module instantiation
This explanation is a little vague, and I can foresee it being the source of future confusion if left as-is. @axic could you perhaps flesh this out?
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@lrettig I was not involved in writing ewasm-kernel, hence the shallowness of the explanation :)
contract_interface.md
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| @@ -9,6 +9,7 @@ Every contract must be stored in the [WebAssembly Binary Encoding](https://githu | |||
| ### Imports | |||
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| A contract can only import symbols specified in the [Ethereum Environment Interface](./eth_interface.md). | |||
| In practice, this means that all imports specified by an ewasm module must be from the `ethereum` namespace, and having a function signature and name directly correspondent to a function specified in the EEI. | |||
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On-chain code does not, but I will make note anyway
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| The use of a [start function](https://webassembly.github.io/spec/core/syntax/modules.html#start-function) is disallowed. | ||
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| The reason for this is that an eWASM VM would need to have access to the memory space of a contract and that must be acquired prior to executing it. |
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I kept it intentionally the old styling in this PR. There's the other PR changing all.
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ok I will update that PR when this is merged
contract_interface.md
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| In the [Webassembly Javascript API](https://webassembly.org/docs/js/) however the start function is executed right during instantiation, which | ||
| leaves no time for the client to acquire the memory area. | ||
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| *Note:* This decision was made on Webassembly version 0xb (pre version 1) and should be revisited. |
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The first 'a' in Webassembly should be capitalized
contract_interface.md
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| The use of a [start function](https://webassembly.github.io/spec/core/syntax/modules.html#start-function) is disallowed. | ||
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| The reason for this is that an eWASM VM would need to have access to the memory space of a contract and that must be acquired prior to executing it. | ||
| In the [Webassembly Javascript API](https://webassembly.org/docs/js/) however the start function is executed right during instantiation, which |
| A contract can only import symbols specified in the [Ethereum Environment Interface](./eth_interface.md). | ||
| A contract can only import symbols specified in the [Ethereum Environment Interface or EEI](./eth_interface.md). | ||
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| In practice, this means that all imports specified by an eWASM module must be from the `ethereum` namespace, |
while implementing my ECI tool, these implicit features of the ECI seemed to be important to explicitly note.