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EIP-2315: updates (#2599)

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Martin Holst Swende 2020-04-16 13:30:18 +02:00 committed by GitHub
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@ -36,25 +36,28 @@ pushes: `0`
1. Pops `1` value from the `stack`, hereafter referred to as `location`.
- 1.1 If the opcode at `location` is not a `BEGINSUB`, abort with error.
2. Pushes the current `pc+1` to the `return_stack`.
2. Pushes the current `pc+1` to the `return_stack`. (See Note 1 below)
- 2.1 If the `return_stack` already has `1023` items, abort with error.
3. Sets the `pc` to `location`.
pops: `1`
pushes: `0` (`return_stack` pushes: `1`)
**Note 1:** The description above lays out the _semantics_ of the `JUMPSUB`. It's up to node implementations to decide the internal representation. For example, a node may decide
to place `PC` on the `return_stack` at `JUMPSUB`, as long as the `RETURNSUB` correctly returns to the `PC+1` location. The internals of the `return_stack` is not one of the
"observable"/consensus-critical parts of the EVM.
##### `RETURNSUB`
1. Pops `1` value form the `return_stack`.
1.1 If the `return_stack` is empty, abort with error
2. Sets `pc` to the popped value
2. Sets `pc` to the popped value (See Note 1 above)
pops: `0` (`return_stack` pops: `1`)
pushes: `0`
**Note:** Values popped from `return_stack` do not need to be validated, since they cannot be set arbitrarily from code, only implicitly by the evm.
**Note2:** A value popped from `return_stack` _may_ be outside of the code length, if the last `JUMPSUB` was the last byte of the `code`. In this case the next opcode is implicitly a `STOP`, which is not an error.
**Note 2:** Values popped from `return_stack` do not need to be validated, since they cannot be set arbitrarily from code, only implicitly by the evm.
**Note 3:** A value popped from `return_stack` _may_ be outside of the code length, if the last `JUMPSUB` was the last byte of the `code`. In this case the next opcode is implicitly a `STOP`, which is not an error.
## Rationale
@ -142,6 +145,25 @@ Bytecode: `0xb75858` (`RETURNSUB`, `PC`, `PC`)
Error: at pc=0, op=RETURNSUB: evm: invalid retsub
```
### Subroutine at end of code
In this example. the JUMPSUB is on the last byte of code. When the subroutine returns, it should hit the 'virtual stop' _after_ the bytecode, and not exit with error
Bytecode: `0x600556b2b75b6003b3`
| Pc | Op | Cost | Stack | RStack |
|-------|-------------|------|-----------|-----------|
| 0 | PUSH1 | 3 | [] | [] |
| 2 | JUMP | 8 | [5] | [] |
| 5 | JUMPDEST | 1 | [] | [] |
| 6 | PUSH1 | 3 | [] | [] |
| 8 | JUMPSUB | 8 | [3] | [] |
| 3 | BEGINSUB | 1 | [] | [ 8] |
| 4 | RETURNSUB | 2 | [] | [ 8] |
| 9 | STOP | 0 | [] | [] |
Consumed gas: `26`
## Implementations
No clients have implemented this proposal as of yet, but there are Draft PRs for