Questions tagged [assembly]
The assembly tag has no usage guidance.
111
questions
2
votes
0answers
23 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
31 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
59 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
29 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
38 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
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
vote
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....
0
votes
0answers
55 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
49 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
38 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
30 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
91 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
65 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
81 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
94 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
109 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
66 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
43 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 ...
0
votes
2answers
64 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
155 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
100 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
45 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
vote
1answer
376 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
18 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
37 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
173 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
37 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
44 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
141 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
74 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
34 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
72 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
0answers
147 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
votes
1answer
357 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
462 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
185 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
190 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
156 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
302 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
320 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
283 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
vote
1answer
42 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
vote
1answer
97 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
votes
2answers
263 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
vote
1answer
245 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
votes
1answer
267 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
vote
2answers
69 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
votes
1answer
62 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
votes
1answer
311 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 ...
