Questions tagged [assembly]
The assembly tag has no usage guidance.
149
questions
0
votes
1answer
29 views
Encode data into a single bytes variable using assembly
I'm currently testing a few things using the Solidity assembly. Basically, what I want to do is
Pack several variables of different type together into one bytes array i.e. similar to what abi....
0
votes
0answers
26 views
How to pass a non-deployed Smart Contract to a deployed contract and call a function on it?
I'm currently trying to pass a Smart Contract (which is NOT deployed) in byte code format as an argument to another Smart Contract (which is deployed).
From within the deployed contract I want to run ...
0
votes
1answer
43 views
Is it possible to access struct field from in-line assembly (Yul) when using ABIEncoderV2?
Is it possible to access struct field from Yul? Ideally it could look like this:
pragma solidity ^0.7.0;
pragma experimental ABIEncoderV2;
contract Sample {
struct S {
uint256 n;
...
0
votes
2answers
50 views
Parameters for delegatecall in inline assembly
I am trying to perform a delegate call from inline-assembly and I am unable to wrap my head around how to access the memory variables assigned outside the assembly block.
function() external payable {
...
0
votes
0answers
9 views
How to deploy a compiled stateless contract and which doesn t have creation code/transaction?
I got a deployed contract bytecode from an internal project which I d like to publish on the mainnet.
The problem is it s just the bytecode without the creation code.
Is there a simpler way to deploy ...
4
votes
1answer
26 views
Copy and deploy a smart contract from opcodes without source code
I extracted opcodes from an already existing and deployed smart contract and I would like to know if it is possible to deploy an exact copy of this contract from its opcodes?
My extracted opcodes ...
0
votes
0answers
17 views
Unable to reference local variable in-line assembly
I am unable to compile a contract that references a local variable in in-line assembly.
Here is the code:
pragma solidity ^0.5.0;
/**
* @dev Contract module that helps prevent reentrant calls to a ...
2
votes
1answer
65 views
Most gas efficient way to check if byte array contains zeroes?
I have a contract that I pass data packed into an array of uint256 (as it's apparently cheaper to use uint256 over bytes32) and each byte in the uint256 contains positions referencing another array of ...
0
votes
1answer
30 views
how do i pass by reference?
I have a couple of questions.
First:
So, In a function, i created memory array. I want to pass this memory by reference to another function..
function test2() public returns(uint a) {
uint[2] ...
1
vote
0answers
37 views
copy array from storage to memory
uint[2] testStorage;
function assemblyStorage() public returns (uint a, uint b){
testStorage[0] = 5;
testStorage[1] = 10;
uint[2] memory testMemory = testStorage;
...
0
votes
1answer
29 views
why does this contract ask to increase gas limit?
string test;
function assemblyStorage() public payable returns (string memory a){
test = "good";
assembly {
a:=sload(0)
}
}
I am trying to return the string ...
1
vote
0answers
18 views
why do i have to specify memory in arguments?
My function body looks like this:
function element(uint a, uint b, uint[2] memory c) public returns(uint e, uint f, uint g, uint k) {
I am wondering why do I put memory keyword before c ? I know that ...
1
vote
0answers
17 views
why mload(0) returns wrong number?
int x; // Storage slot #0
mapping (uint => uint) y; // Storage slot #1
uint [] z; // Storage slot #2
function element() public returns (uint a, uint b, uint c) {
z.push(45);...
1
vote
0answers
47 views
how do storage and memory variable work?
So, in an ordinary programming language, we have stack and heap.
Reference types such as array gets stored in heap. and the variable which holds the address(pointer) of this array is stored in stack..
...
2
votes
1answer
26 views
where does function variables get created?
function element() public returns (uint) {
uint test = 20;
return test;
}
Where would test variable be created ? in memory or stack ?
The funny thing is from testing assembly, I can see that it'...
1
vote
1answer
32 views
sload. assembly with struct - not working in solidity
struct S {
uint128 a;
uint128 b;
}
S test1;
function assemblyStorage() public returns (uint a, uint b, uint c, uint d, uint f, uint g){
test1 = S(5,10);
assembly {
a:=sload(0)
}
}
...
1
vote
0answers
17 views
Trying to understand the ethereum stack
I've been trying to understand the limits of the stack and how it works. It seems like the "Stack too deep" error only happens if there is an assembly block in the function. Without an ...
0
votes
1answer
21 views
Solidity 0.6.x - when is it mandatory to use assembly (with examples)?
Solidity's development is very active and, if compared to several other codes, stable releases are updated quite frequently. Which cases need assembly as mandatory feature for Solidity release 0.6.x? ...
0
votes
0answers
11 views
Can I put the inline assembly code as function argument string?
Assume there is an example as below:
pragma solidity >=0.4.11 <0.6.0;
contract C {
uint b;
function f(uint x) public view returns (uint r) {
assembly {
r := mul(x, ...
1
vote
0answers
25 views
Conditional in assembly
I am trying to use a conditional (like an if statement) in assembly. The only assembly reference site I have ever been able to find says the opcode JUMPI is the way to do this.
Using solc 0.7.0, the ...
0
votes
1answer
87 views
How to get data location for string > 31 length
The documentation says:
bytes and string are encoded identically. For byte arrays that store
data which is 32 or more bytes long, the main slot stores length * 2 +
1 and the data is stored as usual ...
1
vote
2answers
74 views
In assembly… can't get delegatecall to work
Delegatecall can be used in either solidity or assembly.
In solidity, I can get it working with the following code:
bytes memory payload = abi.encodeWithSignature ("get_value(uint16,uint16)",...
0
votes
2answers
45 views
How do i retrieve Eth from a contact that i created?
New to blockchain.. havent a clue.. I managed to create a new contract with Eth. I moved money from MyEtherum Wallet to Metamask and into a contract, somehow? I have no coding experience but need ...
1
vote
1answer
40 views
Parameters on evm opcode create
Why the usual way to create a contract with evm opcodes use add and mload, for example:
bytes memory bytecode = hex"600580600c6000396000b800602a600052b8";
...
assembly {
_address := ...
2
votes
1answer
47 views
Get return value of a low level call
I'd like to get the return value of a low level call.
(bool success, ) = address(0x1234...7890).call{value:0}(callData);
This post discusses a solution that sounds like it should work, but it doesn'...
1
vote
1answer
31 views
How to call sha256 in assembly
I wanna compute sha256 in Solidity Assembly for hash of getting bytes slice.
3
votes
1answer
122 views
Why does Gnosis' MultiSig passes less gas than available in external_call?
Gnosis' MultiSig Wallet substract a fixed amount of gas (34710) when calling an external address.
function external_call(address destination, uint value, uint dataLength, bytes data) internal returns ...
0
votes
1answer
42 views
Calling another contract's state-changing function as view function
In Web3 we can do TestContract.methods.myMethod(myParam).call() to call a state changing function without executing it. But I am wondering if this is possible in Solidity or inline-assembly? So in ...
0
votes
1answer
40 views
Write uints as bytes to create one larger bytes
I would like to take three uints and essentially concatenate them together as one bytes variable. What's the simplest way I can do that? I've seen many posts about people writing full-blown code to ...
0
votes
1answer
128 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
138 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
46 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
91 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
34 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
24 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
49 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
135 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 ...
2
votes
3answers
265 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
33 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
73 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
122 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
86 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
88 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
38 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
0answers
54 views
When I call tranfer_from function, remix saids gas limit exceed
I am owner of the token contract, And when I call transfer_from() function,
remix saids gas limit exceed. my gas limit is 300000.
this is same contract, and call transfer_from() successfully.
"https:/...
1
vote
1answer
45 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
69 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
181 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
31 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{
...
2
votes
1answer
111 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 ...
