mirror of https://github.com/status-im/EIPs.git
323 lines
14 KiB
Markdown
323 lines
14 KiB
Markdown
|
---
|
|||
|
|
eip: 2200
|
|||
|
|
title: Structured Definitions for Net Gas Metering
|
|||
|
|
author: Wei Tang (@sorpaas)
|
|||
|
|
discussions-to: https://github.com/sorpaas/EIPs/issues/1
|
|||
|
|
status: Draft
|
|||
|
|
type: Standards Track
|
|||
|
|
category: Core
|
|||
|
|
created: 2019-07-18
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Simple Summary
|
|||
|
|
|
|||
|
|
This is an EIP that implements net gas metering. It's a combined
|
|||
|
|
version of [EIP-1283] and [EIP-1706], with a structured definition so as
|
|||
|
|
to make it interoperable with other gas changes such as [EIP-1884].
|
|||
|
|
|
|||
|
|
## Abstract
|
|||
|
|
|
|||
|
|
This EIP provides a structured definition of net gas metering changes
|
|||
|
|
for `SSTORE` opcode, enabling new usages for contract storage, and
|
|||
|
|
reducing excessive gas costs where it doesn’t match how most
|
|||
|
|
implementation works.
|
|||
|
|
|
|||
|
|
This is a combination of [EIP-1283] and [EIP-1706].
|
|||
|
|
|
|||
|
|
## Motivation
|
|||
|
|
|
|||
|
|
This EIP proposes a way for gas metering on `SSTORE`, using information
|
|||
|
|
that is more universally available to most implementations, and
|
|||
|
|
require as little change in implementation structures as possible.
|
|||
|
|
|
|||
|
|
* Storage slot’s original value.
|
|||
|
|
* Storage slot’s current value.
|
|||
|
|
* Refund counter.
|
|||
|
|
|
|||
|
|
Usages that benefits from this EIP’s gas reduction scheme includes:
|
|||
|
|
|
|||
|
|
* Subsequent storage write operations within the same call frame. This
|
|||
|
|
includes reentry locks, same-contract multi-send, etc.
|
|||
|
|
* Exchange storage information between sub call frame and parent call
|
|||
|
|
frame, where this information does not need to be persistent outside
|
|||
|
|
of a transaction. This includes sub-frame error codes and message
|
|||
|
|
passing, etc.
|
|||
|
|
|
|||
|
|
The original definition of EIP-1283 created a danger of a new kind of
|
|||
|
|
reentrancy attacks on existing contracts as Solidity by default grants
|
|||
|
|
a "stipend" of 2300 gas to simple transfer calls. This danger is
|
|||
|
|
easily mitigated if `SSTORE` is not allowed in low gasleft state,
|
|||
|
|
without breaking the backward compatibility and the original intention
|
|||
|
|
of EIP-1283.
|
|||
|
|
|
|||
|
|
This EIP also replaces the original EIP-1283 value definitions of gas
|
|||
|
|
by parameters, so that it's more structured, and easier to define
|
|||
|
|
changes in the future.
|
|||
|
|
|
|||
|
|
## Specification
|
|||
|
|
|
|||
|
|
Define variables `SLOAD_GAS`, `SSTORE_SET_GAS`, `SSTORE_RESET_GAS` and
|
|||
|
|
`SSTORE_CLEARS_SCHEDULE`. The old and new values for those variables
|
|||
|
|
are:
|
|||
|
|
|
|||
|
|
* `SLOAD_GAS`: changed from `200` to `800`.
|
|||
|
|
* `SSTORE_SET_GAS`: `20000`, not changed.
|
|||
|
|
* `SSTORE_RESET_GAS`: `5000`, not changed.
|
|||
|
|
* `SSTORE_CLEARS_SCHEDULE`: `15000`, not changed.
|
|||
|
|
|
|||
|
|
Change the definition of EIP-1283 using those variables. The new
|
|||
|
|
specification, combining EIP-1283 and EIP-1706, will look like
|
|||
|
|
below. The terms *original value*, *current value* and *new value* are
|
|||
|
|
defined in EIP-1283.
|
|||
|
|
|
|||
|
|
Replace `SSTORE` opcode gas cost calculation (including refunds) with
|
|||
|
|
the following logic:
|
|||
|
|
|
|||
|
|
* If *gasleft* is less than or equal to gas stipend, fail the current
|
|||
|
|
call frame with 'out of gas' exception.
|
|||
|
|
* If *current value* equals *new value* (this is a no-op), `SLOAD_GAS`
|
|||
|
|
is deducted.
|
|||
|
|
* If *current value* does not equal *new value*
|
|||
|
|
* If *original value* equals *current value* (this storage slot has
|
|||
|
|
not been changed by the current execution context)
|
|||
|
|
* If *original value* is 0, `SSTORE_SET_GAS` is deducted.
|
|||
|
|
* Otherwise, `SSTORE_RESET_GAS` gas is deducted. If *new value* is
|
|||
|
|
0, add `SSTORE_CLEARS_SCHEDULE` gas to refund counter.
|
|||
|
|
* If *original value* does not equal *current value* (this storage
|
|||
|
|
slot is dirty), `SLOAD_GAS` gas is deducted. Apply both of the
|
|||
|
|
following clauses.
|
|||
|
|
* If *original value* is not 0
|
|||
|
|
* If *current value* is 0 (also means that *new value* is not
|
|||
|
|
0), remove `SSTORE_CLEARS_SCHEDULE` gas from refund
|
|||
|
|
counter.
|
|||
|
|
* If *new value* is 0 (also means that *current value* is not
|
|||
|
|
0), add `SSTORE_CLEARS_SCHEDULE` gas to refund counter.
|
|||
|
|
* If *original value* equals *new value* (this storage slot is
|
|||
|
|
reset)
|
|||
|
|
* If *original value* is 0, add `SSTORE_SET_GAS - SLOAD_GAS` to
|
|||
|
|
refund counter.
|
|||
|
|
* Otherwise, add `SSTORE_RESET_GAS - SLOAD_GAS` gas to refund
|
|||
|
|
counter.
|
|||
|
|
|
|||
|
|
An implementation should also note that with the above definition, if
|
|||
|
|
the implementation uses call-frame refund counter, the counter can go
|
|||
|
|
negative. If the implementation uses transaction-wise refund counter,
|
|||
|
|
the counter always stays positive.
|
|||
|
|
|
|||
|
|
## Rationale
|
|||
|
|
|
|||
|
|
This EIP mostly achieves what a transient storage tries to do
|
|||
|
|
([EIP-1087] and [EIP-1153]), but without the complexity of introducing the
|
|||
|
|
concept of "dirty maps", or an extra storage struct.
|
|||
|
|
|
|||
|
|
* We don't suffer from the optimization limitation of
|
|||
|
|
EIP-1087. EIP-1087 requires keeping a dirty map for storage changes,
|
|||
|
|
and implicitly makes the assumption that a transaction's storage
|
|||
|
|
changes are committed to the storage trie at the end of a
|
|||
|
|
transaction. This works well for some implementations, but not for
|
|||
|
|
others. After [EIP-658], an efficient storage cache implementation
|
|||
|
|
would probably use an in-memory trie (without RLP encoding/decoding)
|
|||
|
|
or other immutable data structures to keep track of storage changes,
|
|||
|
|
and only commit changes at the end of a block. For them, it is
|
|||
|
|
possible to know a storage's original value and current value, but
|
|||
|
|
it is not possible to iterate over all storage changes without
|
|||
|
|
incurring additional memory or processing costs.
|
|||
|
|
* It never costs more gas compared with the current scheme.
|
|||
|
|
* It covers all usages for a transient storage. Clients that are easy
|
|||
|
|
to implement EIP-1087 will also be easy to implement this
|
|||
|
|
specification. Some other clients might require a little bit extra
|
|||
|
|
refactoring on this. Nonetheless, no extra memory or processing cost
|
|||
|
|
is needed on runtime.
|
|||
|
|
|
|||
|
|
Regarding `SSTORE` gas cost and refunds, see Appendix for proofs of
|
|||
|
|
properties that this EIP satisfies.
|
|||
|
|
|
|||
|
|
* For *absolute gas used* (that is, actual *gas used* minus *refund*),
|
|||
|
|
this EIP is equivalent to EIP-1087 for all cases.
|
|||
|
|
* For one particular case, where a storage slot is changed, reset to
|
|||
|
|
its original value, and then changed again, EIP-1283 would move more
|
|||
|
|
gases to refund counter compared with EIP-1087.
|
|||
|
|
|
|||
|
|
Examine examples provided in EIP-1087's Motivation (with `SLOAD_GAS` being
|
|||
|
|
`200`):
|
|||
|
|
|
|||
|
|
* If a contract with empty storage sets slot 0 to 1, then back to 0,
|
|||
|
|
it will be charged `20000 + 200 - 19800 = 400` gas.
|
|||
|
|
* A contract with empty storage that increments slot 0 5 times will be
|
|||
|
|
charged `20000 + 5 * 200 = 21000` gas.
|
|||
|
|
* A balance transfer from account A to account B followed by a
|
|||
|
|
transfer from B to C, with all accounts having nonzero starting and
|
|||
|
|
ending balances, it will cost `5000 * 3 + 200 - 4800 = 10400` gas.
|
|||
|
|
|
|||
|
|
In order to keep in place the implicit reentrancy protection of
|
|||
|
|
existing contracts, transactions should not be allowed to modify state
|
|||
|
|
if the remaining gas is lower then the gas stipend given to
|
|||
|
|
"transfer"/"send" in Solidity. These are other proposed remediations
|
|||
|
|
and objections to implementing them:
|
|||
|
|
|
|||
|
|
* Drop EIP-1283 and abstain from modifying `SSTORE` cost
|
|||
|
|
* EIP-1283 is an important update
|
|||
|
|
* It was accepted and implemented on test networks and in clients.
|
|||
|
|
* Add a new call context that permits LOG opcodes but not changes to state.
|
|||
|
|
* Adds another call type beyond existing regular/staticcall
|
|||
|
|
* Raise the cost of `SSTORE` to dirty slots to >=2300 gas
|
|||
|
|
* Makes net gas metering much less useful.
|
|||
|
|
* Reduce the gas stipend
|
|||
|
|
* Makes the stipend almost useless.
|
|||
|
|
* Increase the cost of writes to dirty slots back to 5000 gas, but add
|
|||
|
|
4800 gas to the refund counter
|
|||
|
|
* Still doesn’t make the invariant explicit.
|
|||
|
|
* Requires callers to supply more gas, just to have it refunded
|
|||
|
|
* Add contract metadata specifying per-contract EVM version, and only
|
|||
|
|
apply `SSTORE` changes to contracts deployed with the new version.
|
|||
|
|
|
|||
|
|
## Backwards Compatibility
|
|||
|
|
|
|||
|
|
This EIP requires a hard fork to implement. No gas cost increase is
|
|||
|
|
anticipated, and many contracts will see gas reduction.
|
|||
|
|
|
|||
|
|
Performing `SSTORE` has never been possible with less than 5000 gas, so
|
|||
|
|
it does not introduce incompatibility to the Ethereum mainnet. Gas
|
|||
|
|
estimation should account for this requirement.
|
|||
|
|
|
|||
|
|
## Test Cases
|
|||
|
|
|
|||
|
|
| Code | Used Gas | Refund | Original | 1st | 2nd | 3rd |
|
|||
|
|
|------------------------------------|----------|--------|----------|-----|-----|-----|
|
|||
|
|
| `0x60006000556000600055` | 1612 | 0 | 0 | 0 | 0 | |
|
|||
|
|
| `0x60006000556001600055` | 20812 | 0 | 0 | 0 | 1 | |
|
|||
|
|
| `0x60016000556000600055` | 20812 | 19200 | 0 | 1 | 0 | |
|
|||
|
|
| `0x60016000556002600055` | 20812 | 0 | 0 | 1 | 2 | |
|
|||
|
|
| `0x60016000556001600055` | 20812 | 0 | 0 | 1 | 1 | |
|
|||
|
|
| `0x60006000556000600055` | 5812 | 15000 | 1 | 0 | 0 | |
|
|||
|
|
| `0x60006000556001600055` | 5812 | 4200 | 1 | 0 | 1 | |
|
|||
|
|
| `0x60006000556002600055` | 5812 | 0 | 1 | 0 | 2 | |
|
|||
|
|
| `0x60026000556000600055` | 5812 | 15000 | 1 | 2 | 0 | |
|
|||
|
|
| `0x60026000556003600055` | 5812 | 0 | 1 | 2 | 3 | |
|
|||
|
|
| `0x60026000556001600055` | 5812 | 4200 | 1 | 2 | 1 | |
|
|||
|
|
| `0x60026000556002600055` | 5812 | 0 | 1 | 2 | 2 | |
|
|||
|
|
| `0x60016000556000600055` | 5812 | 15000 | 1 | 1 | 0 | |
|
|||
|
|
| `0x60016000556002600055` | 5812 | 0 | 1 | 1 | 2 | |
|
|||
|
|
| `0x60016000556001600055` | 1612 | 0 | 1 | 1 | 1 | |
|
|||
|
|
| `0x600160005560006000556001600055` | 40818 | 19200 | 0 | 1 | 0 | 1 |
|
|||
|
|
| `0x600060005560016000556000600055` | 10818 | 19200 | 1 | 0 | 1 | 0 |
|
|||
|
|
|
|||
|
|
## Implementation
|
|||
|
|
|
|||
|
|
To be added.
|
|||
|
|
|
|||
|
|
## Appendix: Proof
|
|||
|
|
|
|||
|
|
Because the *storage slot's original value* is defined as the value
|
|||
|
|
when a reversion happens on the *current transaction*, it's easy to
|
|||
|
|
see that call frames won't interfere `SSTORE` gas calculation. So
|
|||
|
|
although the below proof is discussed without call frames, it applies
|
|||
|
|
to all situations with call frames. We will discuss the case
|
|||
|
|
separately for *original value* being zero and not zero, and use
|
|||
|
|
*induction* to prove some properties of `SSTORE` gas cost.
|
|||
|
|
|
|||
|
|
*Final value* is the value of a particular storage slot at the end of
|
|||
|
|
a transaction. *Absolute gas used* is the absolute value of *gas used*
|
|||
|
|
minus *refund*. We use `N` to represent the total number of `SSTORE`
|
|||
|
|
operations on a storage slot. For states discussed below, refer to
|
|||
|
|
*State Transition* in *Explanation* section.
|
|||
|
|
|
|||
|
|
Below we do the proof under the assumption that all parameters are
|
|||
|
|
unchanged, meaning `SLOAD_GAS` is `200`. However, note that the proof
|
|||
|
|
still applies no matter how `SLOAD_GAS` is changed.
|
|||
|
|
|
|||
|
|
### Original Value Being Zero
|
|||
|
|
|
|||
|
|
When *original value* is 0, we want to prove that:
|
|||
|
|
|
|||
|
|
* **Case I**: If the *final value* ends up still being 0, we want to charge `200 *
|
|||
|
|
N` gases, because no disk write is needed.
|
|||
|
|
* **Case II**: If the *final value* ends up being a non-zero value, we want to
|
|||
|
|
charge `20000 + 200 * (N-1)` gas, because it requires writing this
|
|||
|
|
slot to disk.
|
|||
|
|
|
|||
|
|
#### Base Case
|
|||
|
|
|
|||
|
|
We always start at state A. The first `SSTORE` can:
|
|||
|
|
|
|||
|
|
* Go to state A: 200 gas is deducted. We satisfy *Case I* because
|
|||
|
|
`200 * N == 200 * 1`.
|
|||
|
|
* Go to state B: 20000 gas is deducted. We satisfy *Case II* because
|
|||
|
|
`20000 + 200 * (N-1) == 20000 + 200 * 0`.
|
|||
|
|
|
|||
|
|
#### Inductive Step
|
|||
|
|
|
|||
|
|
* From A to A. The previous gas cost is `200 * (N-1)`. The current
|
|||
|
|
gas cost is `200 + 200 * (N-1)`. It satisfy *Case I*.
|
|||
|
|
* From A to B. The previous gas cost is `200 * (N-1)`. The current
|
|||
|
|
gas cost is `20000 + 200 * (N-1)`. It satisfy *Case II*.
|
|||
|
|
* From B to B. The previous gas cost is `20000 + 200 * (N-2)`. The
|
|||
|
|
current gas cost is `200 + 20000 + 200 * (N-2)`. It satisfy
|
|||
|
|
*Case II*.
|
|||
|
|
* From B to A. The previous gas cost is `20000 + 200 * (N-2)`. The
|
|||
|
|
current gas cost is `200 - 19800 + 20000 + 200 * (N-2)`. It satisfy
|
|||
|
|
*Case I*.
|
|||
|
|
|
|||
|
|
### Original Value Not Being Zero
|
|||
|
|
|
|||
|
|
When *original value* is not 0, we want to prove that:
|
|||
|
|
|
|||
|
|
* **Case I**: If the *final value* ends up unchanged, we want to
|
|||
|
|
charge `200 * N` gases, because no disk write is needed.
|
|||
|
|
* **Case II**: If the *final value* ends up being zero, we want to
|
|||
|
|
charge `5000 - 15000 + 200 * (N-1)` gas. Note that `15000` is the
|
|||
|
|
refund in actual definition.
|
|||
|
|
* **Case III**: If the *final value* ends up being a changed non-zero
|
|||
|
|
value, we want to charge `5000 + 200 * (N-1)` gas.
|
|||
|
|
|
|||
|
|
#### Base Case
|
|||
|
|
|
|||
|
|
We always start at state X. The first `SSTORE` can:
|
|||
|
|
|
|||
|
|
* Go to state X: 200 gas is deducted. We satisfy *Case I* because
|
|||
|
|
`200 * N == 200 * 1`.
|
|||
|
|
* Go to state Y: 5000 gas is deducted. We satisfy *Case III* because
|
|||
|
|
`5000 + 200 * (N-1) == 5000 + 200 * 0`.
|
|||
|
|
* Go to state Z: The absolute gas used is `5000 - 15000` where 15000
|
|||
|
|
is the refund. We satisfy *Case II* because `5000 - 15000 + 200 *
|
|||
|
|
(N-1) == 5000 - 15000 + 200 * 0`.
|
|||
|
|
|
|||
|
|
#### Inductive Step
|
|||
|
|
|
|||
|
|
* From X to X. The previous gas cost is `200 * (N-1)`. The current gas
|
|||
|
|
cost is `200 + 200 * (N-1)`. It satisfy *Case I*.
|
|||
|
|
* From X to Y. The previous gas cost is `200 * (N-1)`. The current gas
|
|||
|
|
cost is `5000 + 200 * (N-1)`. It satisfy *Case III*.
|
|||
|
|
* From X to Z. The previous gas cost is `200 * (N-1)`. The current
|
|||
|
|
absolute gas cost is `5000 - 15000 + 200 * (N-1)`. It satisfy *Case
|
|||
|
|
II*.
|
|||
|
|
* From Y to X. The previous gas cost is `5000 + 200 * (N-2)`. The
|
|||
|
|
absolute current gas cost is `200 - 4800 + 5000 + 200 * (N-2)`. It
|
|||
|
|
satisfy *Case I*.
|
|||
|
|
* From Y to Y. The previous gas cost is `5000 + 200 * (N-2)`. The
|
|||
|
|
current gas cost is `200 + 5000 + 200 * (N-2)`. It satisfy *Case
|
|||
|
|
III*.
|
|||
|
|
* From Y to Z. The previous gas cost is `5000 + 200 * (N-2)`. The
|
|||
|
|
current absolute gas cost is `200 - 15000 + 5000 + 200 * (N-2)`. It
|
|||
|
|
satisfy *Case II*.
|
|||
|
|
* From Z to X. The previous gas cost is `5000 - 15000 + 200 *
|
|||
|
|
(N-2)`. The current absolute gas cost is `200 + 10200 + 5000 -
|
|||
|
|
15000 + 200 * (N-2)`. It satisfy *Case I*.
|
|||
|
|
* From Z to Y. The previous gas cost is `5000 - 15000 + 200 *
|
|||
|
|
(N-2)`. The current absolute gas cost is `200 + 15000 + 5000 -
|
|||
|
|
15000 + 200 * (N-2)`. It satisfy *Case III*.
|
|||
|
|
* From Z to Z. The previous gas cost is `5000 - 15000 + 200 *
|
|||
|
|
(N-2)`. The current absolute gas cost is `200 + 5000 - 15000 + 200 *
|
|||
|
|
(N-2)`. It satisfy *Case II*.
|
|||
|
|
|
|||
|
|
## Copyright
|
|||
|
|
|
|||
|
|
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
|
|||
|
|
|
|||
|
|
[EIP-1283]: https://eips.ethereum.org/EIPS/eip-1283
|
|||
|
|
[EIP-1706]: https://eips.ethereum.org/EIPS/eip-1706
|
|||
|
|
[EIP-1884]: https://eips.ethereum.org/EIPS/eip-1884
|
|||
|
|
[EIP-1087]: https://eips.ethereum.org/EIPS/eip-1087
|
|||
|
|
[EIP-1153]: https://eips.ethereum.org/EIPS/eip-1153
|
|||
|
|
[EIP-658]: https://eips.ethereum.org/EIPS/eip-658
|