Questions tagged [assembly]
The assembly tag has no usage guidance.
119
questions
0
votes
1answer
23 views
Factory contract to clone existing contracts
I am researching about Factory contract to clone existing contracts, First is the implementation present at https://github.com/optionality/clone-factory/blob/master/contracts/CloneFactory.sol. I don't ...
2
votes
1answer
35 views
How to get access to the storage mapping through the solidity assembler?
referencing the question How to get access to the storage array through the solidity assembler? I have been trying to figure out how to access the mapping (or variable y from the question). The ...
2
votes
1answer
34 views
is there any advantage of using inline assembly call over address.call?
Is there any advantage of using inline assembly call over address.call?
For example
// address addr
// uint value
// bytes memory data
// using inline assembly
assembly {
call(gas, addr, value,...
1
vote
1answer
23 views
Using assembly to create a fallback function with a return value?
Is it possible to use Solidity assembly to create a fallback function that makes a DELEGATECALL to another contract, and then uses assembly to correctly store the return value of the DELEGATECALL in ...
0
votes
1answer
20 views
why does keccak256 in assembly require 2 arguments?
Why does keccak256() in assembly require 2 arguments? What is the second argument?
assembly {
let foo := keccak256(4)
}
returns error
Function expects 2 arguments but got 1.
1
vote
1answer
15 views
get length of nested array in assembly
How to get length of foo[1] in example below in assembly?
uint[][] foo; // foo.length = 2, foo[1].length = 3
function getLength() returns (uint len) {
assembly {
len := sload(foo) // ...
0
votes
1answer
27 views
Listen to a solidity event from a smart contract function [duplicate]
I have the following event:
event WaitingPlayer2(address indexed player2);
Which I call through:
function partecipateAsPlayer2(address player2) public{
emit WaitingPlayer2(player2);
}
Is ...
1
vote
1answer
49 views
Clone factory and constructor arguments
In my project I'm using a Clone Factory:
https://github.com/optionality/clone-factory/tree/master/contracts
function createClone(address target) external returns (address result) {
bytes20 ...
1
vote
3answers
43 views
Passing constructor arguments to the CREATE assembly instruction in solidity
I have a contract which deploys other contracts by bytecode:
contract DeployContract {
function deploy(bytes calldata _bytecode) external returns(address addr) {
bytes memory bytecode = ...
2
votes
0answers
26 views
In solc 0.4.x assembly, how can I check if a non-constant function returns 'bool' or nothing?
I know how to do it for a constant function, for example:
pragma solidity 0.4.25;
contract Callee0 {function func() external pure returns (bool) {return false;}}
contract Callee1 {function func() ...
2
votes
1answer
42 views
Modifying simple function with inline assembly
I'm trying to write a super simple contract that's gas efficient utilizing inline assembly in solidity. All this function needs to do is create a child smart contract with one function, self destruct....
1
vote
1answer
69 views
Accessing struct fields from assembly block
Say we have the following structure:
struct MyStruct {
uint256 x;
uint256 y;
}
and that it is passed as an argument to some function. Inside that function, we have assembly block from where we ...
1
vote
0answers
44 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 ...
0
votes
1answer
53 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?
2
votes
0answers
24 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
vote
1answer
36 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....
0
votes
0answers
59 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
vote
1answer
79 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
votes
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
vote
1answer
55 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
vote
1answer
39 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
vote
1answer
128 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
vote
1answer
92 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
votes
1answer
105 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
votes
2answers
120 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
votes
2answers
135 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
vote
0answers
84 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
votes
1answer
61 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 ...
1
vote
2answers
95 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
vote
1answer
302 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
votes
1answer
161 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
vote
1answer
54 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).
...
2
votes
1answer
546 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
votes
1answer
20 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
votes
1answer
51 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
votes
1answer
225 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
vote
1answer
39 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
vote
1answer
51 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, ...
4
votes
1answer
218 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
votes
1answer
98 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
votes
1answer
38 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
vote
0answers
97 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
votes
1answer
414 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
votes
2answers
600 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
votes
1answer
223 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
votes
1answer
226 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
vote
1answer
179 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
vote
1answer
347 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
351 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
votes
1answer
305 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 ...
