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Document the possibility of high-level external calls to precompiled contracts #14931

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Document the possibility of high-level external calls to precompiled contracts #14931

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dfa4d1a
Adding clarity on extcalls with precompiled contracts.
mattaereal Mar 8, 2024
b0b73bf
Update docs/introduction-to-smart-contracts.rst
mattaereal Mar 14, 2024
1bf9bcc
Fix on warning structure content in introduction
mattaereal Mar 14, 2024
98de257
Removing recently added suggestion about precompiled contracts from t…
mattaereal Mar 18, 2024
605d6ec
Adding note on high level external calls allowed on precompiled contr…
mattaereal Mar 18, 2024
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34 changes: 25 additions & 9 deletions docs/control-structures.rst
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Expand Up @@ -111,22 +111,38 @@ otherwise, the ``value`` option would not be available.
the ``value`` and ``gas`` settings are lost, only
``feed.info{value: 10, gas: 800}()`` performs the function call.

Due to the fact that the EVM considers a call to a non-existing contract to
always succeed, Solidity uses the ``extcodesize`` opcode to check that
the contract that is about to be called actually exists (it contains code)
and causes an exception if it does not. This check is skipped if the return
data will be decoded after the call and thus the ABI decoder will catch the
case of a non-existing contract.
.. warning::
Due to the fact that the EVM considers a call to a non-existing contract to
always succeed, Solidity uses the ``extcodesize`` opcode to check that
the contract that is about to be called actually exists (it contains code)
and causes an exception if it does not. This check is skipped if the return
data will be decoded after the call and thus the ABI decoder will catch the
case of a non-existing contract.

Note that this check is not performed in case of :ref:`low-level calls <address_related>` which
operate on addresses rather than contract instances.
This check is not performed in case of :ref:`low-level calls <address_related>` which
operate on addresses rather than contract instances.

.. note::
.. warning::
Be careful when using high-level calls to
:ref:`precompiled contracts <precompiledContracts>`,
since the compiler considers them non-existing according to the
above logic even though they execute code and can return data.

.. note::
Since the 0.8.10 release the compiler does not check ``extcodesize`` on
high-level external calls if return data is expected, because an empty code
will be unable to return data, and the ABI decoder will revert.
As a consequence, this allows high-level external calls to precompiled
contracts possible, since they can return data despite having no code
associated with their addresses.

Read about :ref:`precompiled contracts <precompiledContracts>` and
:ref:`low-level calls <address_related>`
for more information.




Function calls also cause exceptions if the called contract itself
throws an exception or goes out of gas.

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