Questions tagged [assembly]
The assembly tag has no usage guidance.
128
questions
1
vote
1answer
18 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
37 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 ...
0
votes
1answer
17 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
35 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'...
0
votes
1answer
23 views
How to call sha256 in assembly
I wanna compute sha256 in Solidity Assembly for hash of getting bytes slice.
3
votes
1answer
101 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
30 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
27 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
64 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
74 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
42 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
51 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
27 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
23 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
45 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
92 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
119 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
32 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
51 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
84 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
69 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
74 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
32 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
52 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
42 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
66 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
120 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
30 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
77 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
67 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
168 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
114 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
125 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
153 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
147 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
101 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
81 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
137 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
396 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
228 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
70 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
738 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
31 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
60 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
289 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
47 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
69 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
303 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
142 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
59 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(...
