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Questions tagged [assembly]

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0answers
27 views

Function selector computed differently for libraries?

As documented in various places, the function selector is computed as the first four bytes of the keccak256 hash of the function header, which consists of the function name followed by the list of ...
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1answer
27 views

How to call ecrecover() in pure assembly?

If I do remember correctly, it’s a contract built‑in in the Ethereum Virtual machine, isn’t it? if yes, what’s the address to call for it?
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0answers
22 views

How to get a call graph for the binary code of a contract?

I need a call graph generator for the assembler level of smart contract code in order to analyse solidity compiler bugs. In that way, porosity is excatly what I need ! However there are too much bugs ...
1
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1answer
33 views

Is the gast cost of '<=' lower than the gas cost of '<'?

I've been debating on whether I should use < or <= in a for loop. So I decided to conduct a small test and verify that their gas costs are the same. Here is my contract: pragma solidity 0.4....
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0answers
54 views

How to get the result from another contract's Optional method while return empty if it does not exist or throws?

For example I want to write a contract where when one passes the address of another contract to it, it will check whether this other contract has the name() function, and if the name() function ...
1
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1answer
38 views

How to construct deployable bytecode from runtime bytecode?

For example I want to redeploy/clone a contract to another address but don't have the original source code, so I only have the runtime bytecode stored on the blockchain. If I try to deploy the runtime ...
0
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1answer
22 views

Call to other contract method return false when two parameters are passed

Caller Contract Called.call(abi.encodeWithSignature("test(address, address)"),empAddress, empContAddress) Called Contract event ad(address); function test(address e, address f)public{ ...
1
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1answer
35 views

Solidity: Saving arbitrary data into bytes array and later parsing it

I want to create a function that receives two addresses and saves them into a bytes array. later a matching function will receive this bytes array and parse the two addresses. function ...
1
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1answer
28 views

Upgradability Proxy ADMIN_SLOT assembly sstore does not update

I'm currently playing around with Proxy Upgradability, and noticed the use of assembly in terms of the new upgraded contract and the slot assigned. Real implementation can be seen here. I have ...
1
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1answer
73 views

Solidity: Raise events via Assembly using log3

I want to raise events from inside a piece of assembly code. I've extended the answer here with the function AssemblyEvent() which currently causes a runtime error. Working example: pragma ...
1
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1answer
57 views

Converting from Assembly to Solidity

I am trying to convert the assembly code into Solidity given at the link: What is a function Selector The code is trying to invoke the function func(...) of Contract1 given below: contract Contract1 ...
2
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1answer
77 views

Using 'call' from a constant function

I am trying to determine the behavior of call when executed from a constant function. Of course, the compiler issues a warning on that: Warning: Function declared as view, but this expression (...
2
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2answers
76 views

Where is the length of an array located in terms of memory layout?

For example, given the following cases: uint[3] memory arr; uint[] memory arr = new uint[](3); Suppose I try to access arr from within an assembly block (using mload, for example). Where (...
2
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2answers
101 views

How can I peek into the stack using inline assembly?

I am specifically interested in calling a function whose return-type is unknown to me. More precisely: The contract which owns the function has had several versions over time My contract may call ...
1
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0answers
63 views

delegatecall (assembly) didn't change state variable in Remix with Web3 Provider

I am trying to test proxy pattern in Remix, which connected to my private chain with Web3 Provider. By the way, miner is working all the time. After invoking add function of Proxy contract, the state ...
0
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1answer
37 views

How does this assembly function work?

From the Docs, how does this operation create a new "memory end"? mstore(0x40, add(o_code, and(add(add(size, 0x20), 0x1f), not(0x1f))) Context: library GetCode { function at(address _addr) public ...
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2answers
58 views

Accessing private variables using assembly

I would like program an oracle service which I would like to charge a fee for. Therefore, I would store the data of interest as a private variable in my oracle contract. This private variable should ...
1
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1answer
125 views

How to get access to the storage array through the solidity assembler?

If the array is located in memory, then all the elements are in sequence, for example: uint256 arrLength = arr.length; assembly{ let offset := sload(arrLength) res:= mload(...
0
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1answer
89 views

Difference in “delegate call via assembly”

I came across a different version of delegate call via assembly and also tried all of them - no different result so far. How does it differ and which is the best version to use? OpenZepplin version: ...
1
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1answer
44 views

Read more than 32 bytes from memory (Assembly)

Assume I am passing a variable bytes (memory) to a function. This variable corresponds to A concatenated with B where A is of size 32 and B is 96 bytes, how can I return A (bytes32) and B (bytes). ...
1
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1answer
299 views

In-line assembly error

I am checking if an address is a smart contract. Similarly to many articles and example-codes out there, i do this within my function: uint32 size; assembly{ size := extcodesize(_to) } if(size &...
2
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1answer
17 views

What is the alternative to using **label** in solidity inline assembly code?

What is the alternative to using label in Solidity inline assembly code? Label is deprecated in new version.
2
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1answer
36 views

Understanding first evm word of reference types in assembly

Given the following function: function getArrayItems(bytes calldata) external returns ( bytes4 _signature, bytes32 _wutIsThis, bytes32 _length, bytes32 _firstItem ) { assembly { ...
2
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1answer
150 views

Solidity assembly function call parameter alignment

I am trying to call a function using assembly. The called function has address parameters. How to use address in assembly call? Called function example: function isSameAddress(address a, address b) ...
1
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1answer
36 views

Is it possible to get a function's original returndata if it is wrapped in an interface that doesn't return anything?

Will a function's returndata persist through a wrapper, even if the wrapper does not support a return value? An example would be as follows: contract OriginalContract { function originalFunction()...
1
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1answer
41 views

why use up all the gasLimit when use assembly and revert together?

try to call erc20 token's transferFrom() using assembly(to save some gas), code like this: pragma solidity ^0.4.24; contract TestAssemblyAndRevert { function test(address from, address to, ...
3
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1answer
118 views

can anyone help to explain calldataload

In the Solidity documentation, the definition of calldataload is: calldataload(p) call data starting from position p (32 bytes) But I am really confused by what is call data. Is the call data of ...
0
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1answer
63 views

How to split bytes32 into multiples of 8 in solidity

I want to split bytes32 into multiples of 8 (in assembly). I have the following code(After referring here): function testAssembly(bytes32 _msg) public pure returns (bytes8 i, bytes8 j, bytes8 k, ...
0
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1answer
32 views

How to get the last n bytes of a bytes32 in assembly?

I have the following code: function getBytes5() public returns (bytes5) { uint256 x = now; bytes memory inBytes = new bytes(32); bytes5 outBytes5; assembly { mstore(...
1
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0answers
64 views

Proxy contract DELEGATECALL to pass a DYNAMIC array to a function in the target contract

I'm trying to get a Proxy contract to correctly do a delegatecall to a function in another 'target' contract. The problem is, that I need to pass a dynamic array as the parameter to this function. Q: ...
0
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0answers
130 views

How to use solidity assembly Opcodes (returndatacopy) to assigning into a variable

I want to write a generic getData function like this below. But I can only return string data or bytes32 data. When I return bytes32 string type data got vanished. When I return string type data ...
0
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1answer
326 views

Convert bytes to uint256[]

I am writing an implementation of ERC777TokensRecipient. So that means a function function tokensReceived(address operator, address from, address to, uint256 amount, bytes data, bytes operatorData) ...
2
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2answers
378 views

how to join two bytes32 values in solidity?

Below is work example of joining two bytes arrays. I wonder how I can join two bytes32 using assembly or solidity? two bytes32 values should serve as an input and a joined bytes32 is an output. ...
7
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1answer
171 views

When did the Ethereum “free memory pointer” change? (6060… -> 6080…)

I have been digging a bit deeper into the Ethereum bytecode with the specific goal to do contract verification from the source code. I noticed, while doing some tests, that the initial bytes of the ...
0
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1answer
182 views

Assembly call instruction address as single integer

The following function is a function of a library (The code is written in Solidity). It has an assembly instruction that I do not understand. Specifically at line call(sub(gas, 2000), 6, 0, input, ...
1
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1answer
147 views

Concatenating byte strings in assembly for call input data

I have the following piece of code in my contract. It's supposed to take in a byte string composed of a uint flag that is followed by a variable list of uint numbers and contruct a call using those ...
1
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1answer
281 views

Assembly opcodes

I need some help understanding assembly functions pragma solidity ^0.4.23; contract Test { function addTest() public pure returns (uint c) { bytes memory b = new bytes(1024); assembly { c:...
2
votes
1answer
304 views

Get return data from delegatecall

I'm using a low level delegatecall to forward my calls to a library. I need to (in this order) : load bytes4 sig into _message from memory load bounty (STRUCT) into _message from storage load bytes ...
2
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1answer
268 views

Optional Multi-Parameter Call to External Contract

I would like to half implement ERC223 for business reasons. This means being able to notify other contracts when they receive tokens, but not revert if the recipient is a contract that doesn't ...
1
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1answer
41 views

Why is mstore not working here? (assembly)

function debug() returns (bytes) { bytes memory ret = new bytes(6); bytes memory word = new bytes(6); word = hex"61626f757400"; assembly { mstore(add(ret, ...
1
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1answer
89 views

Compile standalone assembly

The solidity wiki explains that standalone assembly is also possible. However, I cannot compile it. For example: { mstore(0x40, 0x60) // store the "free memory pointer" // function dispatcher ...
0
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2answers
247 views

Combining two 32 byte values (bytes32) into a 64 byte value

I am passing 64 byte public keys into my solidity function as two 32 byte parts, high 32 bytes and low 32 bytes. How do I combine them back to a 64 byte value in Solidity (cost efficiently)? Looping ...
1
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1answer
228 views

How do I construct a call to contract return string using inline assembly?

pragma solidity ^0.4.21; contract Test1 { function add(int a, int b) returns(string){ //Simply add the two arguments and return return "Qmrwokdkeoiudkeooiskelpdislpeosj;sd[opek;s[pkfe,;...
0
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1answer
254 views

Is there a difference between the call stack and the “normal” stack?

I cannot find any good source on this. The "normal" stack is where all PUSH opcodes put their bytes on. The "call stack" could be some other stack where either call data or addresses are put on - ...
1
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2answers
67 views

Using mstore to copy bytes32 does not work, why?

Why does mstore(c, p) not copy p to c? function test()returns (bytes32) { bytes32 c; bytes32 p = 0xFF; assembly { mstore(c, p) } return c; }
0
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1answer
59 views

Convert two int128 variables to Bytes32 and back

For Bytes32 to 2x int128 I have working code. I've adapted code from this stack Exchange answer function bytes32to2xint128(bytes32 z) pure public returns (int128 x, int128 y){ bytes16[2] memory ...
0
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1answer
289 views

How can assembly be used to add bytes together? [duplicate]

To store data on the blockchain, a storage container bytes[6] data is used, each array stores maximum amount based on block gas limit. Can assembly be used to add those 6 arrays together, and return ...
5
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2answers
2k views

How to convert bytes to uint in Solidity

Hey is there a way to convert bytes to uint in Solidity?
3
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2answers
364 views

Returning values from Solidity function that does not define a return?

I'm a bit confused by the code at this smart contract, which is part of the Aragon project code: function delegatedFwd( address _dst, bytes _calldata, uint256 _minReturnSize) internal { ...
0
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1answer
142 views

Forward call to another smart contract

I have created a smart contract using a factory method pattern as follows: contract MyContractFactory is Ownable { function create(...) onlyOwner public returns (MyContract) { return new ...