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Istanbul hardfork will break DepositableDelegateProxy #549

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ritzdorf opened this issue Aug 24, 2019 · 15 comments · Fixed by #551

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@ritzdorf
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commented Aug 24, 2019

Background

The upcoming Istanbul Ethereum hardfork contains the EIP-1884. EIP-1884 will, besides other things, raise the gas cost of the EVM SLOAD instruction from 200 to 800 gas.

Issue Description

The fallback function of DepositableDelegateProxy:

    function () external payable {
        // send / transfer
        if (gasleft() < FWD_GAS_LIMIT) {
            require(msg.value > 0 && msg.data.length == 0);
            require(isDepositable());
            emit ProxyDeposit(msg.sender, msg.value);
        } else { // all calls except for send or transfer
            address target = implementation();
            delegatedFwd(target, msg.data);
        }
    }

and the relevant isDepositable() function:

    function isDepositable() public view returns (bool) {
        return DEPOSITABLE_POSITION.getStorageBool();
    }

Basically, as the code comment says, in case the fallback function was triggered by a .send() or .transfer(), which only send along 2300 gas, the first branch will be executed. Then, isDepositable() will be executed and a ProxyDeposit event will be emitted.

Currently, the execution of this function consumes 1759 gas. During the execution one SLOAD is executed due to isDepositable(). Hence, the gas cost after the hardfork will be 1759 + 600 = 2359 which will run out of gas. Hence, the transaction will generally revert.

Example

The contract is deployed at address 0x0a74d136fafed0f8d58ce4b7307283695ec7a0b6 and its fallback function was recently executed with 2300 gas as part of the transaction 0x14a4a43b4e9759aac86bb0ae7e5926850406ff1c43ea571239563ff781474ae0.

Additional Information

ChainSecurity has conducted some analysis on the effects of EIP-1884. The intermediate results can be found here.

Martin Holst Swende has collected information on the effects of EIP-1884 here.

Contact

Feel free to contact hubert@chainsecurity.com or @HRitzdorf on Telegram in case of questions or comments.

@welcome

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commented Aug 24, 2019

Thanks for opening your first issue in aragonOS! Someone will circle back soon ⚡

@sohkai

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commented Aug 26, 2019

Hmm, this is problematic indeed. This has various ramifications throughout Aragon's existing smart contracts, the largest of which is an organization's Vault being able to receive ETH through simple contract transfers (e.g. Finance -> Vault deposit, Agent receiving ETH from CDPs, Compound, etc.).

Given that we are really close to the limit, we could optimize this a bit to have it fit inside 2300, but it presents a migration problem for all existing 600+ Aragon organizations deployed to date (and for the foreseeable future) as we can't upgrade the proxy contracts.

@ritzdorf

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commented Aug 26, 2019

Thank you for the explanation.

I agree that an optimization seems feasible. The easiest option might be to modify the event. Otherwise, the optimization becomes slightly harder. The current version of the event (counting only LOG1 not the necessary setup) consumes 1262 gas, together with the new cost of SLOAD (800) that is already 2062 gas spent.

@holiman

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commented Aug 27, 2019

it presents a migration problem for all existing 600+ Aragon organizations deployed to date (and for the foreseeable future) as we can't upgrade the proxy contracts.

Could you elaborate on this? I am not at all familiar with Aragon, really, so please outline how big of a problem, and what the impact or possible consequences could be.

@izqui

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commented Aug 27, 2019

@holiman the contracts that compose Aragon organizations use the DelegateProxy pattern for upgradeability. Thanks to this we can upgrade most of the logic of the contracts, except for the code in the proxy. The code that allows these contracts to receive ETH when sent with 2300 gas had to be implemented in the proxy code directly, as deferring this to the implementation code (performing the delegatecall) made it go over the 2300 gas limit.

The issue right now is that there are ~680 contracts (one per organization) that will no longer be able to receive ETH when sent from a smart contract, including receiving ETH from another Aragon organization, after EIP-1884 is activated.

The migration path for existing organizations would be quite tedious, as each organization would need to deploy a new proxy contract, modify sensitive permissions in the organization and move all the funds to this new proxy contract that can execute the fallback in under 2300 gas.

Because we don't have control over any of the deployed organizations, each of them would have to execute the process on their own. Even though we could build tools for this, it would be a painful process.

@holiman

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commented Aug 27, 2019

Ok. Is this a correct assumption?

  • "all of those affected contracts will use exactly 2359 gas, in the affected code path"

If so, it seems that this issue could be resolved by simply lowering the cost of LOG operations by a little bit. It would be interesting to see a trace of the execution.

@ritzdorf

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commented Aug 28, 2019

@holiman Here is the gzipped trace of the example execution mentioned above (0x14a4a43b4e9759aac86bb0ae7e5926850406ff1c43ea571239563ff781474ae0). The relevant fallback function gets executed on depth 8.

I don't know if all affected contracts will use exactly this amount of gas as this is the only one where I know the exact address so that I could check. I currently do not see how to efficiently get all the vault addresses from the explorer, otherwise I would be happy to check.

@holiman

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commented Aug 28, 2019

Here is the execution trace with nicer formatting. The trace for some reason contains the wrong values for gasCost for many opcodes, I have no idea why.
Part one:

╔════════════════════════════════════Operations═════════════════════════════════════╗│┌──────────────────────────────────────Op──────────────────────────────────────┐│
│║STEP       PC          OPNAME    OPCODE  GAS   GASCOST DEPTH REFUND                ║││                                                                              ││
│║12176 5094 (0x13e6) CALL         0xf1   164370 9700    7     0                     ║││ pc      5094 (0x13e6)                                                        ││
│║12177 0 (0x0)       PUSH1        0x60   2300   0       8     0                     ║││ opcode  0xf1                                                                 ││
│║12178 2 (0x2)       PUSH1        0x60   2297   0       8     0                     ║││ opName  CALL                                                                 ││
│║12179 4 (0x4)       MSTORE       0x52   2294   12      8     0                     ║││ gasCost 9700                                                                 ││
│║12180 5 (0x5)       PUSH1        0x60   2282   12      8     0                     ║││ gas     164370                                                               ││
│║12181 7 (0x7)       CALLDATASIZE 0x36   2279   12      8     0                     ║││ memSize 0                                                                    ││
│║12182 8 (0x8)       LT           0x10   2277   12      8     0                     ║││ addr    NA                                                                   ││
│║12183 9 (0x9)       PUSH2        0x61   2274   12      8     0                     ║││ Pops    gas,address,value,in offset,in size,out offset,out size              ││
│║12184 12 (0xc)      JUMPI        0x57   2271   12      8     0                     ║││ Pushes  exitcode (1 for success)                                             ││
│║12185 108 (0x6c)    JUMPDEST     0x5b   2261   12      8     0                     ║││                                                                              ││
│║12186 109 (0x6d)    PUSH1        0x60   2260   12      8     0                     ║││                                                                              ││
│║12187 111 (0x6f)    PUSH2        0x61   2257   12      8     0                     ║││                                                                              ││
│║12188 114 (0x72)    GAS          0x5a   2254   12      8     0                     ║││                                                                              ││
│║12189 115 (0x73)    LT           0x10   2252   12      8     0                     ║││                                                                              ││
│║12190 116 (0x74)    ISZERO       0x15   2249   12      8     0                     ║││                                                                              ││
│║12191 117 (0x75)    PUSH2        0x61   2246   12      8     0                     ║││                                                                              ││
│║12192 120 (0x78)    JUMPI        0x57   2243   12      8     0                     ║││                                                                              ││
│║12193 121 (0x79)    PUSH1        0x60   2233   12      8     0                     ║││                                                                              ││
│║12194 123 (0x7b)    CALLVALUE    0x34   2230   12      8     0                     ║││                                                                              ││
│║12195 124 (0x7c)    GT           0x11   2228   12      8     0                     ║││                                                                              ││
│║12196 125 (0x7d)    DUP1         0x80   2225   12      8     0                     ║││                                                                              ││
│║12197 126 (0x7e)    ISZERO       0x15   2222   12      8     0                     ║││                                                                              ││
│║12198 127 (0x7f)    PUSH2        0x61   2219   12      8     0                     ║││                                                                              ││
│║12199 130 (0x82)    JUMPI        0x57   2216   12      8     0                     ║││                                                                              ││
│║12200 131 (0x83)    POP          0x50   2206   12      8     0                     ║││                                                                              ││
│║12201 132 (0x84)    CALLDATASIZE 0x36   2204   12      8     0                     ║││                                                                              ││
│║12202 133 (0x85)    ISZERO       0x15   2202   12      8     0                     ║││                                                                              ││
│║12203 134 (0x86)    JUMPDEST     0x5b   2199   12      8     0                     ║││                                                                              ││
│║12204 135 (0x87)    ISZERO       0x15   2198   12      8     0                     ║││                                                                              ││
│║12205 136 (0x88)    ISZERO       0x15   2195   12      8     0                     ║││                                                                              ││
│║12206 137 (0x89)    PUSH2        0x61   2192   12      8     0                     ║││                                                                              ││
│║12207 140 (0x8c)    JUMPI        0x57   2189   12      8     0                     ║││                                                                              ││
│║12208 145 (0x91)    JUMPDEST     0x5b   2179   12      8     0                     ║││                                                                              ││
│║12209 146 (0x92)    PUSH2        0x61   2178   12      8     0                     ║││                                                                              ││
│║12210 149 (0x95)    PUSH2        0x61   2175   12      8     0                     ║││                                                                              ││
│║12211 152 (0x98)    JUMP         0x56   2172   12      8     0                     ║││                                                                              ││
│║12212 483 (0x1e3)   JUMPDEST     0x5b   2164   12      8     0                     ║││                                                                              ││
│║12213 484 (0x1e4)   PUSH1        0x60   2163   12      8     0                     ║││                                                                              ││
│║12214 486 (0x1e6)   PUSH2        0x61   2160   12      8     0                     ║││                                                                              ││
│║12215 489 (0x1e9)   PUSH32       0x7f   2157   12      8     0                     ║││                                                                              ││
│║12216 522 (0x20a)   PUSH2        0x61   2154   12      8     0                     ║││                                                                              ││
│║12217 525 (0x20d)   JUMP         0x56   2151   12      8     0                     ║││                                                                              ││
│║12218 701 (0x2bd)   JUMPDEST     0x5b   2143   12      8     0                     ║││                                                                              ││
│║12219 702 (0x2be)   SLOAD        0x54   2142   200     8     0                     ║││                                                                              ││
│╚═══════════════════════════════════════════════════════════════════════════════════╝│└──────────────────────────────────────────────────────────────────────────────┘│
├─────────────────────────────────────────────────────────────────────────────────────┼────────────────────────────────────────────────────────────────────────────────┤
│┌───────────────────────────────────────Stack───────────────────────────────────────┐│┌────────────────────────────────────Memory────────────────────────────────────┐│
││POS                                                             DATA DESC          │││         00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f [ -- ascii -- ]      ││
││00                                                                 0 gas           │││00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││01                           a74d136fafed0f8d58ce4b7307283695ec7a0b6 address       │││00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││02                                                  10a741a462780000 value         │││00000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││03                                                               180 in offset     │││00000030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││04                                                                 0 in size       │││00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││05                                                               180 out offset    │││00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 80 ................     ││
││06                                                                 0 out size      │││00000060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││07                                                               180               │││00000070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││08                                                  10a741a462780000               │││00000080 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││09                                                                 0               │││00000090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 60 ...............`     ││
││10                           a74d136fafed0f8d58ce4b7307283695ec7a0b6               │││000000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││11                                                                80               │││000000b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
│└───────────────────────────────────────────────────────────────────────────────────┘│└──────────────────────────────────────────────────────────────────────────────┘│

Part two:

╔════════════════════════════════════Operations═════════════════════════════════════╗│┌──────────────────────────────────────Op──────────────────────────────────────┐│
│║STEP       PC        OPNAME   OPCODE  GAS   GASCOST DEPTH REFUND                   ║││                                                                              ││
│║12219 702 (0x2be)   SLOAD     0x54   2142   200     8     0                        ║││ pc      298 (0x12a)                                                          ││
│║12220 703 (0x2bf)   SWAP1     0x90   1942   200     8     0                        ║││ opcode  0x0                                                                  ││
│║12221 704 (0x2c0)   JUMP      0x56   1939   200     8     0                        ║││ opName  STOP                                                                 ││
│║12222 526 (0x20e)   JUMPDEST  0x5b   1931   200     8     0                        ║││ gasCost 1262                                                                 ││
│║12223 527 (0x20f)   SWAP1     0x90   1930   200     8     0                        ║││ gas     541                                                                  ││
│║12224 528 (0x210)   POP       0x50   1927   200     8     0                        ║││ memSize 0                                                                    ││
│║12225 529 (0x211)   SWAP1     0x90   1925   200     8     0                        ║││ addr    NA                                                                   ││
│║12226 530 (0x212)   JUMP      0x56   1922   200     8     0                        ║││ Pops                                                                         ││
│║12227 153 (0x99)    JUMPDEST  0x5b   1914   200     8     0                        ║││ Pushes                                                                       ││
│║12228 154 (0x9a)    ISZERO    0x15   1913   200     8     0                        ║││                                                                              ││
│║12229 155 (0x9b)    ISZERO    0x15   1910   200     8     0                        ║││                                                                              ││
│║12230 156 (0x9c)    PUSH2     0x61   1907   200     8     0                        ║││                                                                              ││
│║12231 159 (0x9f)    JUMPI     0x57   1904   200     8     0                        ║││                                                                              ││
│║12232 164 (0xa4)    JUMPDEST  0x5b   1894   200     8     0                        ║││                                                                              ││
│║12233 165 (0xa5)    PUSH1     0x60   1893   200     8     0                        ║││                                                                              ││
│║12234 167 (0xa7)    DUP1      0x80   1890   200     8     0                        ║││                                                                              ││
│║12235 168 (0xa8)    MLOAD     0x51   1887   3       8     0                        ║││                                                                              ││
│║12236 169 (0xa9)    CALLER    0x33   1884   3       8     0                        ║││                                                                              ││
│║12237 170 (0xaa)    DUP2      0x81   1882   3       8     0                        ║││                                                                              ││
│║12238 171 (0xab)    MSTORE    0x52   1879   9       8     0                        ║││                                                                              ││
│║12239 172 (0xac)    CALLVALUE 0x34   1870   9       8     0                        ║││                                                                              ││
│║12240 173 (0xad)    PUSH1     0x60   1868   9       8     0                        ║││                                                                              ││
│║12241 175 (0xaf)    DUP3      0x82   1865   9       8     0                        ║││                                                                              ││
│║12242 176 (0xb0)    ADD       0x1    1862   9       8     0                        ║││                                                                              ││
│║12243 177 (0xb1)    MSTORE    0x52   1859   6       8     0                        ║││                                                                              ││
│║12244 178 (0xb2)    DUP2      0x81   1853   6       8     0                        ║││                                                                              ││
│║12245 179 (0xb3)    MLOAD     0x51   1850   3       8     0                        ║││                                                                              ││
│║12246 180 (0xb4)    PUSH32    0x7f   1847   3       8     0                        ║││                                                                              ││
│║12247 213 (0xd5)    SWAP3     0x92   1844   3       8     0                        ║││                                                                              ││
│║12248 214 (0xd6)    SWAP2     0x91   1841   3       8     0                        ║││                                                                              ││
│║12249 215 (0xd7)    DUP2      0x81   1838   3       8     0                        ║││                                                                              ││
│║12250 216 (0xd8)    SWAP1     0x90   1835   3       8     0                        ║││                                                                              ││
│║12251 217 (0xd9)    SUB       0x3    1832   3       8     0                        ║││                                                                              ││
│║12252 218 (0xda)    SWAP1     0x90   1829   3       8     0                        ║││                                                                              ││
│║12253 219 (0xdb)    SWAP2     0x91   1826   3       8     0                        ║││                                                                              ││
│║12254 220 (0xdc)    ADD       0x1    1823   3       8     0                        ║││                                                                              ││
│║12255 221 (0xdd)    SWAP1     0x90   1820   3       8     0                        ║││                                                                              ││
│║12256 222 (0xde)    LOG1      0xa1   1817   1262    8     0                        ║││                                                                              ││
│║12257 223 (0xdf)    PUSH2     0x61   555    1262    8     0                        ║││                                                                              ││
│║12258 226 (0xe2)    JUMP      0x56   552    1262    8     0                        ║││                                                                              ││
│║12259 296 (0x128)   JUMPDEST  0x5b   544    1262    8     0                        ║││                                                                              ││
│║12260 297 (0x129)   POP       0x50   543    1262    8     0                        ║││                                                                              ││
│║12261 298 (0x12a)   STOP      0x0    541    1262    8     0                        ║││                                                                              ││
│║12262 5095 (0x13e7) SWAP4     0x93   155211 9700    7     0                        ║││                                                                              ││
│╚═══════════════════════════════════════════════════════════════════════════════════╝│└──────────────────────────────────────────────────────────────────────────────┘│

The bulk of the cost is from

LOG1      0xa1   1817   1262

The LOG1 operation details:

│┌───────────────────────────────────────Stack───────────────────────────────────────┐│┌────────────────────────────────────Memory────────────────────────────────────┐│
││POS                                                             DATA DESC          │││         00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f [ -- ascii -- ]      ││
││00                                                                80 mStart        │││00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││01                                                                40 mSize         │││00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││02  15eeaa57c7bd188c1388020bcadc2c436ec60d647d36ef5b9eb3c742217ddee1 topic         │││00000020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││03                                                                 0               │││00000030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││                                                                                   │││00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││                                                                                   │││00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80 ................     ││
││                                                                                   │││00000060 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││                                                                                   │││00000070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││                                                                                   │││00000080 00 00 00 00 00 00 00 00 00 00 00 00 e2 7c af 89 .............|..     ││
││                                                                                   │││00000090 51 7a 33 da be 83 6b b7 40 ff 96 cc 37 51 a0 86 Qz3...k.@...7Q..     ││
││                                                                                   │││000000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................     ││
││                                                                                   │││000000b0 00 00 00 00 00 00 00 00 10 a7 41 a4 62 78 00 00 ..........A.bx..     ││
│└───────────────────────────────────────────────────────────────────────────────────┘│└──────────────────────────────────────────────────────────────────────────────┘

So it uses 1 topic, and 0x40 bytes of memory. There is no memory expansion, but 375 + 1 * 375 (topics) + 0x40 * 8 (logdata) = 1262 gas.

@sohkai

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commented Aug 28, 2019

Ok. Is this a correct assumption?

"all of those affected contracts will use exactly 2359 gas, in the affected code path"

Yes, this should be correct.

I currently do not see how to efficiently get all the vault addresses from the explorer, otherwise I would be happy to check.

If this is necessary we can send a list of addresses, although they will all act the same as the one you used.

@tkstanczak

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commented Aug 28, 2019

pasting here the solution I proposed on AllCoreDev(for reference)
I also think that in this particular scenario LOG, LOG_TOPIC cost reduction to 300, 375 would suffice

EIP-1884
Solution 1) (stipend fix only)

The idea is to use the fact that when calling with a non-zero value, 9000 gas is used instead of 700.
Moreover this 9000 is calculated as a cost of the caller and callee account balance updates (two state updates).
Since these accounts will be cached by the clients, an attacker would have to keep calling a different predeployed contract each time to take advantage of the discounts proposed below in a loop and (in order to cause clients to load and update non-cached accounts). Attacker would have to pay 9000 for each call and significant amount of gas for each of the target contract deployments before the attack and additional gas for storing the target contract addresses in the calling contract storage before executing an attack. In such scenario, the attack should be prohibitively expensive.

(in such attack we get 9000 (non-zero value call) - 700 (standard call cost) gas for free to minimize the impact of the proposed stipend discount.

Let us introduce a short (2-byte) STIPEND_USE counter on EVM state (state at the current EVM call).
Let us introduce a boolean STIPEND_AVAILABLE variable on EVM state (for better performance of gas updates).

At the beginning of any call set STIPEND_AVAILABLE to true when TRANSFER_VALUE > 0 && CALL_DEPTH > 0.

STIPEND_USE starts at 0
each time GAS_USED is increased
if (STIPEND_AVAILABLE) increase the STIPEND_USE by the same amount
then if STIPEND_USE >= 2300 SET STIPEND_AVAILABLE to false
if (!STIPEND_AVAILABLE) do nothing
Now set price of SLOAD to:

800 if NOT(STIPEND_AVAILABLE)
200 otherwise
Now set price of BALANCE to:

700 if NOT(STIPEND_AVAILABLE)
400 otherwise
Now set price of EXTCODEHASH to:

700 if NOT(STIPEND_AVAILABLE)
400 otherwise


The client memory cost is ~3 bytes per call depth
The client performance cost is a ulong to short cast + short addition + short comparison when STIPEND_USE is below 2300, then one boolean check for each gas update
Maintenance cost - amortized since we can use this solution for any repricing in the future, additional logic in GAS_USED updates.

@ritzdorf

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commented Aug 28, 2019

@holiman's proposal of lowering the cost of LOG seems to be a very convenient solution for this particular contract.

@holiman : I don't see LOG as risky in your vmstats analysis. So was LOG currently overpriced?

@MicahZoltu

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commented Aug 30, 2019

Regardless of the immediate term solution to this problem, dapp developers (e.g., Aragon) should not assume that gas costs will remain constant over time. They are designed to change as operational costs of various operations change over time relative to each other. You should not be using .transfer and .send and instead protect against reentrancy via other patterns.

On top of that, .transfer and .send do not give enough of a gas stipend for smart wallets to execute advanced functionality on receipt, so along with the fact that they may break in some future fork, they currently break when interacting with any smart wallet that is actually smart (e.g., a smart wallet that proxies funds on receipt).

@holiman

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commented Aug 30, 2019

they currently break when interacting with any smart wallet that is actually smart (e.g., a smart wallet that proxies funds on receipt).

Well, it's not been easy for contract devs. This is also considered an anti-pattern, where the more recommended route has been to let the final recipient(s) pull, instead of "pushing" it to them.

An underlying problem is that there hasn't existed an CALL type that means "no state changes but log is allowed". Otherwise "STATICCALLWITHLOGS" could have been a great primitive for transfer

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commented Aug 30, 2019

@holiman : I don't see LOG as risky in your vmstats analysis. So was LOG currently overpriced?

So LOG is one of those which aren't well covered by vmstats, like SSTORE. They have post-execution side-effects, which aren't captured at runtime. So their cost needs to take that into account, not just the speed of executing the op.

@MicahZoltu

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commented Aug 30, 2019

Yes, I'm a big fan of the mailbox pattern and encourage its use when it makes sense to solve the problem. This way you can let the transfer happen with as much gas as the recipient needs to do whatever accounting it wants to on receipt. I don't know enough about this particular situation in Aragon to know whether that is an appropriate solution here, but I do think something along those lines should be used instead of gas stipends.

@izqui izqui closed this in #551 Sep 3, 2019

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