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CREATE opcode: what does it really do?

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2

I am looking at the docs, but cannot really understand what CREATE opcode does. I can tell that CREATE does create a new smart contract from a memory chunk, pass the gas value to this new contract, then returns. But before returning, does it execute the new contract?

This confuses me because looking at the disassembly code of the smart contract bytecode, after CREATE, I cannot see any call to CALL after that, but then I still see a call to RETURNDATASIZE, which I suppose only happen after CALL. Without CALL, where it get returned data from?

Any enlighten, please?

opcode create

share|improve this question

asked 1 hour ago

user311703user311703

1806

add a comment | 

2

I am looking at the docs, but cannot really understand what CREATE opcode does. I can tell that CREATE does create a new smart contract from a memory chunk, pass the gas value to this new contract, then returns. But before returning, does it execute the new contract?

This confuses me because looking at the disassembly code of the smart contract bytecode, after CREATE, I cannot see any call to CALL after that, but then I still see a call to RETURNDATASIZE, which I suppose only happen after CALL. Without CALL, where it get returned data from?

Any enlighten, please?

opcode create

share|improve this question

asked 1 hour ago

user311703user311703

1806

add a comment | 

I am looking at the docs, but cannot really understand what CREATE opcode does. I can tell that CREATE does create a new smart contract from a memory chunk, pass the gas value to this new contract, then returns. But before returning, does it execute the new contract?

This confuses me because looking at the disassembly code of the smart contract bytecode, after CREATE, I cannot see any call to CALL after that, but then I still see a call to RETURNDATASIZE, which I suppose only happen after CALL. Without CALL, where it get returned data from?

Any enlighten, please?

opcode create

share|improve this question

asked 1 hour ago

user311703user311703

1806

share|improve this question

asked 1 hour ago

user311703user311703

1806

share|improve this question

asked 1 hour ago

user311703user311703

1806

asked 1 hour ago

user311703user311703

1806

asked 1 hour ago

user311703user311703

1806

1 Answer
1

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5

CREATE, in a way, does a built in CALL. What actually happens is that the data passed to call isn't the contract bytecode, it's the init bytecode.

When CREATE opcode is executed, the EVM creates a call frame in the context of the new contract (e.g. address(this) is the new contracts address). This executes the data passed to CREATE as the code, which in higher level languages is basically the constructor. At the end of this init stuff, it returns the actual code of the contract that is stored in the state trie.

The easiest way to think about it, which is also fairly accurate, is that the Solidity compiler takes all the executional code of the contract, compiles it to bytecode, and adds it as a return statement at the end of the constructor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

flygoingflygoing

7,580931

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ah, so CREATE when creating a contract actually returns the contract bytecode, right? then after that, CALL will actually executes the contract?
  
  – user311703
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Please could you tell me what is the best way to track/trace what is really happening at bytecode level? Does Remix a good tool to do this?
  
  – user311703
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  CREATE executes the code passed to it, and that code returns the contact bytecode, yes. Just wanted to be clear on that
  
  – flygoing
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you need to a call a function after it's created, then yeah, there would be a CALL right after. Remix is a pretty good way to track/trace on the bytecode level, it has pretty good EVM debugging tools for stepping in/out of bytecode
  
  – flygoing
  54 mins ago
  

  
  
  
  

add a comment | 

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5

CREATE, in a way, does a built in CALL. What actually happens is that the data passed to call isn't the contract bytecode, it's the init bytecode.

When CREATE opcode is executed, the EVM creates a call frame in the context of the new contract (e.g. address(this) is the new contracts address). This executes the data passed to CREATE as the code, which in higher level languages is basically the constructor. At the end of this init stuff, it returns the actual code of the contract that is stored in the state trie.

The easiest way to think about it, which is also fairly accurate, is that the Solidity compiler takes all the executional code of the contract, compiles it to bytecode, and adds it as a return statement at the end of the constructor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

flygoingflygoing

7,580931

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ah, so CREATE when creating a contract actually returns the contract bytecode, right? then after that, CALL will actually executes the contract?
  
  – user311703
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Please could you tell me what is the best way to track/trace what is really happening at bytecode level? Does Remix a good tool to do this?
  
  – user311703
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  CREATE executes the code passed to it, and that code returns the contact bytecode, yes. Just wanted to be clear on that
  
  – flygoing
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you need to a call a function after it's created, then yeah, there would be a CALL right after. Remix is a pretty good way to track/trace on the bytecode level, it has pretty good EVM debugging tools for stepping in/out of bytecode
  
  – flygoing
  54 mins ago
  

  
  
  
  

add a comment | 

5

CREATE, in a way, does a built in CALL. What actually happens is that the data passed to call isn't the contract bytecode, it's the init bytecode.

When CREATE opcode is executed, the EVM creates a call frame in the context of the new contract (e.g. address(this) is the new contracts address). This executes the data passed to CREATE as the code, which in higher level languages is basically the constructor. At the end of this init stuff, it returns the actual code of the contract that is stored in the state trie.

The easiest way to think about it, which is also fairly accurate, is that the Solidity compiler takes all the executional code of the contract, compiles it to bytecode, and adds it as a return statement at the end of the constructor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

flygoingflygoing

7,580931

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ah, so CREATE when creating a contract actually returns the contract bytecode, right? then after that, CALL will actually executes the contract?
  
  – user311703
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Please could you tell me what is the best way to track/trace what is really happening at bytecode level? Does Remix a good tool to do this?
  
  – user311703
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  CREATE executes the code passed to it, and that code returns the contact bytecode, yes. Just wanted to be clear on that
  
  – flygoing
  55 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you need to a call a function after it's created, then yeah, there would be a CALL right after. Remix is a pretty good way to track/trace on the bytecode level, it has pretty good EVM debugging tools for stepping in/out of bytecode
  
  – flygoing
  54 mins ago
  

  
  
  
  

add a comment | 

CREATE, in a way, does a built in CALL. What actually happens is that the data passed to call isn't the contract bytecode, it's the init bytecode.

When CREATE opcode is executed, the EVM creates a call frame in the context of the new contract (e.g. address(this) is the new contracts address). This executes the data passed to CREATE as the code, which in higher level languages is basically the constructor. At the end of this init stuff, it returns the actual code of the contract that is stored in the state trie.

The easiest way to think about it, which is also fairly accurate, is that the Solidity compiler takes all the executional code of the contract, compiles it to bytecode, and adds it as a return statement at the end of the constructor.

share|improve this answer

edited 1 hour ago

answered 1 hour ago

flygoingflygoing

7,580931

share|improve this answer

edited 1 hour ago

answered 1 hour ago

flygoingflygoing

7,580931

answered 1 hour ago

flygoingflygoing

7,580931

answered 1 hour ago

flygoingflygoing

7,580931