Questions tagged [assembly]
The assembly tag has no usage guidance.
288
questions
1
vote
1
answer
37
views
how come loading the funcSig from data isn't enough, you have to shift it also to use it in the rest of the code/function
basically we have this function
function FlaggedMethods(
bytes memory data
) public returns (address) {
bytes4 funcSig;
assembly {
// Shift right by 224 bits ...
- 13
0
votes
2
answers
29
views
Make Uniswap v2 swap through inline assembly
I'm trying to make swap tokens in smart contract using Uniswap V2. My main goal is to make part where you need to work with Uniswap router as assembly block.
I'm not good in assembly, so I need your ...
- 23
1
vote
1
answer
23
views
Cannot getting a storage variable from another contract using inline-assembly
I am trying to develop myself on inline-assembly. There are two contracts: CryptoDevs and Whitelist. In the assembly, i copied the whole code of whitelist contract instance into cryptodevs memory. ...
2
votes
0
answers
10
views
How can i implement `MinimalBeaconProxy`?
I'm trying to make MinimalBeaconProxy. But seems like the assembly codes don't work. Can I get some advice of this codes?
Contracts
contract BeaconProxyCreator {
constructor(address beacon) ...
- 21
0
votes
0
answers
13
views
how this function do in the stack, calldata, and memory
I am not familiar with the inline assembly. May I ask what happened in the arrLength method and how it operates in stack, memory, and calldata
pragma solidity 0.4.5;
contract Test {
// for ...
- 61
0
votes
1
answer
53
views
Inline Assembly: RETURN opcode can't not work. Failed to decode output
I know that: return(p, s): end execution, return data mem[p…(p+s)).
I want to return something in memory but not a multiple of bytes32. For example, I want to return 1 byte:
pragma solidity 0.8.20;
...
- 61
2
votes
1
answer
89
views
Trying to use CREATE opcode to deploy a new contract instance using bytecode of a deployed contract
I am trying to get the bytecode from a deployed contract, then by using that bytecode, use the CREATE opcode to deploy a new instance of that contract.
Here is the code I'm trying out (but to no avail)...
- 41
1
vote
1
answer
68
views
How to shift elements in array using inline assembly?
Taking a memory array [1,2,3], is it possible to us shr/shl to make the array [2,3,1]?
- 598
3
votes
2
answers
81
views
Remix Assembly vs. Solidity Compiler Assembly
I am just diving into EVM assembly and am a little confused about the following.
I have the following simple contract:
pragma solidity >=0.8.1;
contract MyTest {}
When I compile it using Remix, I ...
- 729
2
votes
3
answers
203
views
How to decode a nested encodePacked?
The structure of the encoding is
abi.encodePacked(
abi.encodePacked(
address,
uint256,
uint256,
address,
uint256,
address,
...
- 598
1
vote
0
answers
31
views
I have low level method that calculates log2, but I don't exactly understand how it works
Somebody, please, can you explain step by step how it assembly code exactly works?
function log2(uint x) private pure returns(uint y) {
assembly {
let arg := x
x := sub(x,1)
...
1
vote
1
answer
517
views
Is it possible to reverse the gas used in case of using revert?
I try to refund gas to the minimum even after using revert with the following example.
uint A = IERC20(base).balanceOf(address(this));
IERC20(token).transfer(owner,1000000);
then I run swaps ...
0
votes
1
answer
23
views
I m trying to add additional parameter in fulfillBasicOrder but it gives me error
When I add additional parameter in fulfillBasicOrder it gives me error of InvalidBasicOrderParameterEncoding
Please help me out how can I add additional parameter in this function as I have less ...
- 31
1
vote
1
answer
56
views
Why doesn't the Yul instruction `div` work just like the high-level division operator?
I noticed that the following Solidity functions are not equivalent:
function a(int256 x) pure returns (uint256 result) {
assembly {
result := div(sub(0, x), x)
}
}
function b(int256 ...
- 16.8k
1
vote
2
answers
527
views
What is calldata offset for dynamic calldata arrays?
The Solidity docs say this about dynamic calldata arrays:
For dynamic calldata arrays, you can access their calldata offset (in bytes) and length (number of elements) using x.offset and x.length
But ...
- 16.8k
2
votes
0
answers
54
views
Is there any way to bubble up custom errors without using low-level assembly?
Is there any way to bubble up custom errors without using low-level assembly?
Say you have a custom error defined like this:
contract For {
error Unauthorized();
function reverWithError() ...
- 16.8k
1
vote
2
answers
249
views
Is it safe to open SLOAD to any contract?
I am running into issue of contract size over the limit when deploying my contract. So, I have decided to open SLOAD in my getter so that any contract can read from it.
function readBySlot(uint256 ...
- 405
0
votes
0
answers
99
views
How to use keccak256 in assembly instead of keccack256(abi.encodePacked(address))?
I'm trying to use assembly to compare the gas usage of two implementations of the same function.
The following works correctly:
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.17;
import ...
0
votes
0
answers
24
views
Difference between TIMESTAMP and block.timestamp
I have two questions:
I went to the link:
https://ethervm.io/
and saw TIMESTAMP in the Mnemonic column and block.timestamp in Stack output. Please guide me what is the difference between Mnemonic ...
- 1,406
0
votes
0
answers
21
views
How to shift an array of structs so that the first index is the last— with Yul?
Is it possible to use Yul to shift an array of structs? Have been trying (including by encoding the struct array) to no success.
Using this for a an array of struct with 2 uint256 members:
assembly { ...
- 598
0
votes
2
answers
209
views
Convert bytes20 to address in assembly
Can you convert a bytes20 to address in assembly (not solidity-typecasting)?
If so, how?
- 675
1
vote
0
answers
48
views
How to values in mapping type struct with solidity assembly?
I have a special needs, store the mapping type struct with assembly code. thank you very for everyone who can response this question.
Need your help how to write something in assembly
Here is how I am ...
- 11
0
votes
1
answer
128
views
Grab last 12 bytes of a bytes32
How do I grab the last 12 bytes of a bytes32 in assembly?
For example, the last 12 bytes of bytes32 num = 0xdeb02111e4e5fa8c7c05e983a3446893a36d12ad6d79206163636f756e740000
Thanks!
- 675
0
votes
1
answer
29
views
how to return tightly packed storage values in assembly
I have a contract with 2 tightly packed values in storage slot1, how do I return the second address value with assembly?
Contract MyContract{
bool a;
address b;
function getAddress() public ...
- 283
0
votes
1
answer
44
views
Grab the last 32 bytes of 64-bytes input
In assembly, how do I grab the last 32 bytes in a 64-bytes input?
I know that this code is for grabbing the first 32:
bytes32 half;
assembly {
half := mload(add(accData2, 32))
}
- 675
0
votes
1
answer
71
views
How to understand the difference between transfer and function call using assembly call(g,a,v,in,insize,out,outsize)
I understand that if there is an external function call, it will use all 7 parameters of the call(g,a,v,in,insize,out,outsize). However, I got a question I know low-level transfers like .transfer() ...
- 15
3
votes
2
answers
779
views
Yul/Inline Assembly: Revert with a custom error message
I am learning Yul for my Bachelor's thesis and I am currently stuck on understanding a small code segment with require and revert functions.
A simple require function in Solidity ...
require(...
- 33
1
vote
2
answers
203
views
How to get internal calls Calldata in solidity?
How to get signature of setA() when user is calling setB() for below code snippet ?
contract Sig {
function setA() public {
// How to get function signature of `setA()` at this location while ...
- 11
0
votes
1
answer
289
views
How could you replicate foundry's vm.load cheatcode with solidity code?
I assume it would need assembly and potentially a delegatecall function, but I have been stuck trying to get anything that could work. The idea is that we would input the contract address and the ...
- 302
0
votes
2
answers
120
views
Appending address array through assembly
I have an assembly part which creates an address which I want to append to an array in an address => address[] mapping. The code works if I use push() but I am trying to reduce gas usage and have ...
- 1
2
votes
1
answer
80
views
Does the free memory pointer need padding?
This code is taken from the solidity documentation.
library GetCode {
function at(address addr) public view returns (bytes memory code) {
assembly {
// retrieve the size of the ...
- 23
1
vote
2
answers
106
views
Why does storing values at non-32 multiple memory locations spill over to next location?
Take this line for example (Yul):
mstore(0x24, 0x0443455243)
If it was mstore(0x20, 0x0443455243), then the entire value would have been stored at location 0x20.
However, if 0x24 is used, I'd expect ...
- 111
0
votes
1
answer
39
views
Most gas efficient way to convert uint256 into a handful of uint8s
I am working on a card game. I have a problem where I am choosing to store a representation of 32 uint8s inside one uint256 word in order to save on gas. I store the uint256 word and then want to ...
- 1,710
1
vote
0
answers
41
views
Why evm assembly push4 sometimes doesn't push the value in parameter?
I'm analyzing the fail of this tx on goerli
My question is not really about the tx, but about a strange behaviour when I debug it on remix.
I'm calling a proxy who called the implementation with ...
- 41
1
vote
1
answer
177
views
Is there a way of getting the stateRoot of the last block in a contract?
So i was curious if you could write a contract, that retrieves the StateRoot from the last mined block. I found a Repo from Keydonix, who used the stateRoot from previous blocks to calculate a more ...
- 13
0
votes
0
answers
16
views
Accessing an internal function in my contract via assembly in another function
I have this block of code that compares hashes of bytes and I would like to convert directly into assembly:
uint skipPointer; // prevents excess search if a match has been found
uint ...
- 31
0
votes
0
answers
86
views
Gnosis sqrt function vs Uniswap sqrt function
The Uniswap sqrt function makes sense to me. I can input 100 and it returns 10. Gnosis on the other hand has a gnarly 368 lines of code expressing the same function (I think) but the return value is ...
- 144
1
vote
1
answer
176
views
How do I manipulate the elements of a memory array in assembly?
Simple example:
Let's say I have a function that takes a fixed size array, finds the largest number in it, and returns another fixed size array in memory with the largest number as the last index:
...
- 31
0
votes
1
answer
58
views
Free memory point manipulation in solmate library
I am trying to learn a little bit of yul and came across a scenario in the solmate library I don't quite understand. In all of the instances when they are appending addresses to the free memory ...
0
votes
1
answer
48
views
get uint value inside a bytes32 slice
I have the following code:
function test_bytes(bytes32 test) external pure returns(bytes3 idx,uint256 idx2)
{
//test = ...
- 1
0
votes
1
answer
19
views
Problem with expensive function
I have next code :
struct Data
{
uint id;
string name;
string Surname
string moreInfo;
}
mapping(address => Data[]) private ownerauto;
address[] private owners
string[] ...
- 11
1
vote
0
answers
328
views
Solidity assembly code - calldatacopy, delegatecall
I have been trying to understand how assembly code works,spending lots of hours, but I could not.
Please help me
Basically, I am digging into a proxy contract, and I do not really understand ...
- 199
1
vote
2
answers
36
views
What is the return value of this asembly code?
Taken from this repository
/// @notice Generate number
function asmbl() public view returns (uint8 b) {
assembly {
let c := add(27, 16)
mstore(0x80, c)
{ let d := add(...
- 195
0
votes
0
answers
74
views
Solidity assembly function returns false on forked blockchain
I try to simulate submitting transaction to Multisig contract and confirming transaction by other multisig members by impersonating their account on Hardhat with forking.
I managed submitting and ...
- 1
1
vote
1
answer
31
views
Transalte Assembly(Solidity)
I want translate code to assembly, but i don't understand , how i can get data from string ( or bytes)
Example String: 123 --> uint 123
for (uint256 i = 0; i < bytes(_str).length; i++)
{
...
- 11
0
votes
1
answer
31
views
Why is memory used by RETURN misaligned compared to how it was allocated?
I am experimenting with evmone and evmc to execute some simple assembly code snippets on EVM. I wrote a test that is supposed to return 0x42 as output data. The code goes as follows:
PUSH 0x42
PUSH ...
- 103
1
vote
1
answer
265
views
What are the two arguments in revert opcode?
I am trying to understand the revert opcode and how it works . I understood that it will stop the execution of current context and return 0 to the calling context.
It seems it also takes in 2 ...
- 123
0
votes
1
answer
97
views
Finding max of a memory array in assembly
Practicing my solidity assembly skills and I'm using foundry to test this function. For most inputs it works, but fails when
There is a 0 present in the array
Possibly duplicate values present in the ...
- 1
2
votes
2
answers
497
views
Solidity Assembly Code create2 function
I am new to solidity, can you please explain the create2 function?
assembly {
pair := create2(0, add(bytecode, 32), mload(bytecode), salt)
}
- 25
0
votes
1
answer
159
views
What is the "solidity scratch pad"?
I'm reading up on upgradable proxies, came across this in openzeppelin.
//solium-disable-next-line
assembly {
// Copy msg.data. We take full control of memory in this inline assembly
...
- 867