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docs: Add storage change status analysis #418

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docs: Add storage change status analysis #418

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928062b
Extend storage status
chfast Aug 4, 2022
3f8b64d
Refactor MockedHost's storage value
chfast Aug 10, 2022
d7a6ced
Add full EIP-2200 implementation to MockedHost
chfast Aug 11, 2022
d8611ac
rule → clause
chfast Aug 11, 2022
d2fd3f5
rule → clause
chfast Aug 11, 2022
abac5e6
docs: Add storage change status analysis
chfast Sep 6, 2019
8c8608c
docs: Name the storage change statuses
chfast Sep 6, 2019
d9b3250
docs: use canonical eips.ethereum.org link
axic May 7, 2020
3a095fa
docs: update it with the final 2200 version?
axic May 7, 2020
ab3a03b
docs update
chfast Aug 11, 2022
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14 changes: 9 additions & 5 deletions bindings/go/evmc/host.go
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Original file line number Diff line number Diff line change
Expand Up @@ -36,11 +36,15 @@ const (
type StorageStatus int

const (
StorageUnchanged StorageStatus = C.EVMC_STORAGE_UNCHANGED
StorageModified StorageStatus = C.EVMC_STORAGE_MODIFIED
StorageModifiedAgain StorageStatus = C.EVMC_STORAGE_MODIFIED_AGAIN
StorageAdded StorageStatus = C.EVMC_STORAGE_ADDED
StorageDeleted StorageStatus = C.EVMC_STORAGE_DELETED
StorageModifiedAgain StorageStatus = C.EVMC_STORAGE_MODIFIED_AGAIN
StorageAdded StorageStatus = C.EVMC_STORAGE_ADDED
StorageDeleted StorageStatus = C.EVMC_STORAGE_DELETED
StorageModified StorageStatus = C.EVMC_STORAGE_MODIFIED
StorageDeletedAdded StorageStatus = C.EVMC_STORAGE_DELETED_ADDED
StorageModifiedDeleted StorageStatus = C.EVMC_STORAGE_MODIFIED_DELETED
StorageDeletedRestored StorageStatus = C.EVMC_STORAGE_DELETED_RESTORED
StorageAddedDeleted StorageStatus = C.EVMC_STORAGE_ADDED_DELETED
StorageModifiedRestored StorageStatus = C.EVMC_STORAGE_MODIFIED_RESTORED
)

func goAddress(in C.evmc_address) Address {
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2 changes: 1 addition & 1 deletion bindings/go/evmc/host_test.go
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Expand Up @@ -20,7 +20,7 @@ func (host *testHostContext) GetStorage(addr Address, key Hash) Hash {
}

func (host *testHostContext) SetStorage(addr Address, key Hash, value Hash) (status StorageStatus) {
return StorageUnchanged
return StorageModifiedAgain
}

func (host *testHostContext) GetBalance(addr Address) Hash {
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4 changes: 2 additions & 2 deletions bindings/rust/evmc-vm/src/types.rs
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Expand Up @@ -99,8 +99,8 @@ mod tests {
#[test]
fn storage_status() {
assert_eq!(
StorageStatus::EVMC_STORAGE_UNCHANGED,
ffi::evmc_storage_status::EVMC_STORAGE_UNCHANGED
StorageStatus::EVMC_STORAGE_MODIFIED_AGAIN,
ffi::evmc_storage_status::EVMC_STORAGE_MODIFIED_AGAIN
);
assert_eq!(
StorageStatus::EVMC_STORAGE_MODIFIED,
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169 changes: 169 additions & 0 deletions docs/storage_change_status.md
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@@ -0,0 +1,169 @@
# Storage change status

> Analysis of possible storage change statuses in [EIP-2200].

## Specification

1. If *gasleft* is less than or equal to gas stipend, fail the current
call frame with 'out of gas' exception.
2. If *current value* equals *new value* (this is a no-op), `SLOAD_GAS`
is deducted.
3. If *current value* does not equal *new value*
1. If *original value* equals *current value* (this storage slot has
not been changed by the current execution context)
1. If *original value* is 0, `SSTORE_SET_GAS` is deducted.
2. Otherwise, `SSTORE_RESET_GAS` gas is deducted.
1. If *new value* is 0,
add `SSTORE_CLEARS_SCHEDULE` gas to refund counter.
2. If *original value* does not equal *current value* (this storage
slot is dirty), `SLOAD_GAS` gas is deducted. Apply both of the
following clauses.
1. If *original value* is not 0
1. If *current value* is 0 (also means that *new value* is not
0), remove `SSTORE_CLEARS_SCHEDULE` gas from refund
counter.
2. If *new value* is 0 (also means that *current value* is not
0), add `SSTORE_CLEARS_SCHEDULE` gas to refund counter.
2. If *original value* equals *new value* (this storage slot is
reset)
1. If *original value* is 0, add `SSTORE_SET_GAS - SLOAD_GAS` to
refund counter.
2. Otherwise, add `SSTORE_RESET_GAS - SLOAD_GAS` gas to refund
counter.

## Cost constants

| Constant | Value |
| -------- | ----- |
| SLOAD | 800 |
| SET | 20000 |
| RESET | 5000 |
| CLEARS | 15000 |

## Storage change statuses

- `0` - a zero storage value,
- `X` - non-zero storage value,
- `Y` - non-zero storage value different from `X`,
- `Z` - non-zero storage value different form `X` and `Y`,

<table>
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Show resolved Hide resolved
<thead>
<tr>
<th>name</th>
<th>o</th>
<th>c</th>
<th>v</th>
<th>dirty?</th>
<th>clause</th>
<th>gas cost</th>
<th>gas refund</th>
</tr>
</thead>
<tbody>
<tr>
<td rowspan="7">NOOP</td>
<td>0</td><td>0</td><td>0</td>
<td>no</td>
<td>2</td>
<td rowspan="7">800 = SLOAD</td>
<td rowspan="7">0</td>
</tr>
<tr>
<td>X</td><td>0</td><td>0</td>
<td>yes</td>
<td>2</td>
</tr>
<tr>
<td>0</td><td>Y</td><td>Y</td>
<td>yes</td>
<td>2</td>
</tr>
<tr>
<td>X</td><td>Y</td><td>Y</td>
<td>yes</td>
<td>2</td>
</tr>
<tr>
<td>Y</td><td>Y</td><td>Y</td>
<td>no</td>
<td>2</td>
</tr>
<tr>
<td>0</td><td>Y</td><td>Z</td>
<td>yes</td>
<td>3.2</td>
</tr>
<tr>
<td>X</td><td>Y</td><td>Z</td>
<td>yes</td>
<td>3.2</td>
</tr>
<tr>
<td>ADDED</td>
<td>0</td><td>0</td><td>Z</td>
<td>no</td>
<td>3.1.1</td>
<td>20000 = SET</td>
<td>0</td>
</tr>
<tr>
<td>DELETED</td>
<td>X</td><td>X</td><td>0</td>
<td>no</td>
<td>3.1.2.1</td>
<td>5000 = RESET</td>
<td>15000 = CLEARS</td>
</tr>
<tr>
<td>MODIFIED</td>
<td>X</td><td>X</td><td>Z</td>
<td>no</td>
<td>3.1.2</td>
<td>5000 = RESET</td>
<td>0</td>
</tr>
<tr>
<td>deleted added</td>
<td>X</td><td>0</td><td>Z</td>
<td>yes</td>
<td>3.2.1.1</td>
<td>800 = SLOAD</td>
<td>-15000 = -CLEARS</td>
</tr>
<tr>
<td>MODIFIED_DELETED</td>
<td>X</td><td>Y</td><td>0</td>
<td>yes</td>
<td>3.2.1.2</td>
<td>800 = SLOAD</td>
<td>15000 = CLEARS</td>
</tr>
<tr>
<td>DELETED_RESTORED</td>
<td>X</td><td>0</td><td>X</td>
<td>yes</td>
<td>3.2.1.1 + 3.2.2.2</td>
<td>800 = SLOAD</td>
<td>-15000 = -CLEARS</td>
</tr>
<tr>
<td>ADDED_DELETED</td>
<td>0</td><td>Y</td><td>0</td>
<td>yes</td>
<td>3.2.2.1</td>
<td>800 = SLOAD</td>
<td>19200 = SET - SLOAD</td>
</tr>
<tr>
<td>MODIFIED_RESTORED</td>
<td>X</td><td>Y</td><td>X</td>
<td>yes</td>
<td>3.2.2.2</td>
<td>800 = SLOAD</td>
<td>4200 = RESET - SLOAD</td>
</tr>
</tbody>
</table>

[EIP-2200]: https://eips.ethereum.org/EIPS/eip-2200
2 changes: 1 addition & 1 deletion examples/example_host.cpp
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Expand Up @@ -77,7 +77,7 @@ class ExampleHost : public evmc::Host
auto prev_value = account.storage[key];
account.storage[key] = value;

return (prev_value == value) ? EVMC_STORAGE_UNCHANGED : EVMC_STORAGE_MODIFIED;
return (prev_value == value) ? EVMC_STORAGE_MODIFIED_AGAIN : EVMC_STORAGE_MODIFIED;
}

evmc::uint256be get_balance(const evmc::address& addr) const noexcept final
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104 changes: 91 additions & 13 deletions include/evmc/evmc.h
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Expand Up @@ -502,36 +502,114 @@ typedef evmc_bytes32 (*evmc_get_storage_fn)(struct evmc_host_context* context,
* notation is used:
* - 0 is zero value,
* - X != 0 (X is any value other than 0),
* - Y != X, Y != 0 (Y is any value other than X and 0),
* - Z != Y (Z is any value other than Y),
* - the "->" means the change from one value to another.
* - Y != 0, Y != X, (Y is any value other than X and 0),
* - Z != 0, Z != X, Z != X (Z is any value other than Y and X and 0),
* - the "o -> c -> v" triple describes the change status in the context of:
* - o: original value (cold value before a transaction started),
* - c: current storage value,
* - v: new storage value to be set.
*
* The order of elements follows EIPs introducing net storage gas costs:
* - EIP-2200: https://eips.ethereum.org/EIPS/eip-2200,
* - EIP-1283: https://eips.ethereum.org/EIPS/eip-1283.
*/
enum evmc_storage_status
{
/**
* The value of a storage item has been left unchanged: 0 -> 0 and X -> X.
* The value of a storage item has been left unchanged or has been modified again
* in the transaction context. This is the group of "no-op" cases related to
* minimal gas cost.
* 0|X -> 0 -> 0 (current value unchanged)
* 0|X|Y -> Y -> Y (current value unchanged)
* 0|X -> Y -> Z (modified previously added/modified value)
*
* This is "catch all remaining" status. I.e. if all other statuses are correctly matched
* this status should be assigned to all remaining cases.
*
* This corresponds to the EIP-2200 clause 2 or clause 3.2 without sub-clauses, where:
* c == v or (c != v, o != c, (o == 0 or (o != 0, c != 0, v != 0)), o != v)
*/
EVMC_STORAGE_MODIFIED_AGAIN = 0,

/**
* A new storage item is added by changing
* the current clean zero to a nonzero value.
* 0 -> 0 -> Z
*
* This corresponds to the EIP-2200 clause 3.1.1 where:
* c != v, o == c, c == 0.
*/
EVMC_STORAGE_UNCHANGED = 0,
EVMC_STORAGE_ADDED = 1,

/**
* The value of a storage item has been modified: X -> Y.
* A storage item is deleted by changing
* the current clean nonzero to the zero value.
* X -> X -> 0
*
* This corresponds to the v == 0 variant of the EIP-2200 clause 3.1.2 where:
* c != v, o == c, c != 0, v == 0.
*/
EVMC_STORAGE_MODIFIED = 1,
EVMC_STORAGE_DELETED = 2,

/**
* A storage item has been modified after being modified before: X -> Y -> Z.
* A storage item is modified by changing
* the current clean nonzero to other nonzero value.
* X -> X -> Z
*
* This corresponds to the v != 0 variant of the EIP-2200 clause 3.1.2 where:
* c != v, o == c, c != 0, v != 0.
*/
EVMC_STORAGE_MODIFIED_AGAIN = 2,
EVMC_STORAGE_MODIFIED = 3,

/**
* A new storage item has been added: 0 -> X.
* A storage item is added by changing
* the current dirty zero to a nonzero value other than the original value.
* X -> 0 -> Z
*
* This corresponds to the EIP-2200 clause 3.2.1.1 without the clause 3.2.2, where:
* c != v, o != c, o != 0, c == 0, o != v.
*/
EVMC_STORAGE_ADDED = 3,
EVMC_STORAGE_DELETED_ADDED = 4,

/**
* A storage item has been deleted: X -> 0.
* A storage item is deleted by changing
* the current dirty nonzero to the zero value and the original value is not zero.
* X -> Y -> 0
*
* This corresponds to the EIP-2200 clause 3.2.1.2 where:
* c != v, o != c, o != 0, v == 0 (therefore o != v).
*/
EVMC_STORAGE_MODIFIED_DELETED = 5,

/**
* A storage item is added by changing
* the current dirty zero to the original value.
* X -> 0 -> X
*
* This corresponds to the EIP-2200 clauses 3.2.1.1 and 3.2.2.2 combined, where:
* c != v, o != c, o != 0, c == 0, o == v.
*/
EVMC_STORAGE_DELETED_RESTORED = 6,

/**
* A storage item is deleted by changing
* the current dirty nonzero to the original zero value.
* 0 -> Y -> 0
*
* This corresponds to the EIP-2200 clause 3.2.2.1 where:
* c != v, o != c, o == 0, c != 0, o == v, v == 0.
*/
EVMC_STORAGE_ADDED_DELETED = 7,

/**
* A storage item is modified by changing
* the current dirty nonzero to the original nonzero value other than the current value.
* X -> Y -> X
*
* This corresponds to the EIP-2200 clause 3.2.2.2 where:
* c != v, o != c, o != 0, c != 0, o == v, v != 0.
*/
EVMC_STORAGE_DELETED = 4
EVMC_STORAGE_MODIFIED_RESTORED = 8
};


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