mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
Merge pull request #11212 from ethereum/docs-asm
[DOCS] Added documentation about --asm flag
This commit is contained in:
Harikrishnan Mulackal
GitHub
commit
ecf9a44dac
192
docs/analysing-compilation-output.rst
Normal file
192
docs/analysing-compilation-output.rst
Normal file
@ -0,0 +1,192 @@
|
||||
.. index:: analyse, asm
|
||||
|
||||
#############################
|
||||
Analysing the Compiler Output
|
||||
#############################
|
||||
|
||||
It is often useful to look at the assembly code generated by the compiler. The generated binary,
|
||||
i.e., the output of ``solc --bin contract.sol``, is generally difficult to read. It is recommended
|
||||
to use the flag ``--asm`` to analyse the assembly output. Even for large contracts, looking at a
|
||||
visual diff of the assembly before and after a change is often very enlightening.
|
||||
|
||||
Consider the following contract (named, say ``contract.sol``):
|
||||
|
||||
.. code-block:: Solidity
|
||||
|
||||
// SPDX-License-Identifier: GPL-3.0
|
||||
pragma solidity >=0.5.0 <0.9.0;
|
||||
contract C {
|
||||
function one() public pure returns (uint) {
|
||||
return 1;
|
||||
}
|
||||
}
|
||||
|
||||
The following would be the output of ``solc --asm contract.sol``
|
||||
|
||||
.. code-block:: none
|
||||
|
||||
======= contract.sol:C =======
|
||||
EVM assembly:
|
||||
/* "contract.sol":0:86 contract C {... */
|
||||
mstore(0x40, 0x80)
|
||||
callvalue
|
||||
dup1
|
||||
iszero
|
||||
tag_1
|
||||
jumpi
|
||||
0x00
|
||||
dup1
|
||||
revert
|
||||
tag_1:
|
||||
pop
|
||||
dataSize(sub_0)
|
||||
dup1
|
||||
dataOffset(sub_0)
|
||||
0x00
|
||||
codecopy
|
||||
0x00
|
||||
return
|
||||
stop
|
||||
|
||||
sub_0: assembly {
|
||||
/* "contract.sol":0:86 contract C {... */
|
||||
mstore(0x40, 0x80)
|
||||
callvalue
|
||||
dup1
|
||||
iszero
|
||||
tag_1
|
||||
jumpi
|
||||
0x00
|
||||
dup1
|
||||
revert
|
||||
tag_1:
|
||||
pop
|
||||
jumpi(tag_2, lt(calldatasize, 0x04))
|
||||
shr(0xe0, calldataload(0x00))
|
||||
dup1
|
||||
0x901717d1
|
||||
eq
|
||||
tag_3
|
||||
jumpi
|
||||
tag_2:
|
||||
0x00
|
||||
dup1
|
||||
revert
|
||||
/* "contract.sol":17:84 function one() public pure returns (uint) {... */
|
||||
tag_3:
|
||||
tag_4
|
||||
tag_5
|
||||
jump // in
|
||||
tag_4:
|
||||
mload(0x40)
|
||||
tag_6
|
||||
swap2
|
||||
swap1
|
||||
tag_7
|
||||
jump // in
|
||||
tag_6:
|
||||
mload(0x40)
|
||||
dup1
|
||||
swap2
|
||||
sub
|
||||
swap1
|
||||
return
|
||||
tag_5:
|
||||
/* "contract.sol":53:57 uint */
|
||||
0x00
|
||||
/* "contract.sol":76:77 1 */
|
||||
0x01
|
||||
/* "contract.sol":69:77 return 1 */
|
||||
swap1
|
||||
pop
|
||||
/* "contract.sol":17:84 function one() public pure returns (uint) {... */
|
||||
swap1
|
||||
jump // out
|
||||
/* "#utility.yul":7:125 */
|
||||
tag_10:
|
||||
/* "#utility.yul":94:118 */
|
||||
tag_12
|
||||
/* "#utility.yul":112:117 */
|
||||
dup2
|
||||
/* "#utility.yul":94:118 */
|
||||
tag_13
|
||||
jump // in
|
||||
tag_12:
|
||||
/* "#utility.yul":89:92 */
|
||||
dup3
|
||||
/* "#utility.yul":82:119 */
|
||||
mstore
|
||||
/* "#utility.yul":72:125 */
|
||||
pop
|
||||
pop
|
||||
jump // out
|
||||
/* "#utility.yul":131:353 */
|
||||
tag_7:
|
||||
0x00
|
||||
/* "#utility.yul":262:264 */
|
||||
0x20
|
||||
/* "#utility.yul":251:260 */
|
||||
dup3
|
||||
/* "#utility.yul":247:265 */
|
||||
add
|
||||
/* "#utility.yul":239:265 */
|
||||
swap1
|
||||
pop
|
||||
/* "#utility.yul":275:346 */
|
||||
tag_15
|
||||
/* "#utility.yul":343:344 */
|
||||
0x00
|
||||
/* "#utility.yul":332:341 */
|
||||
dup4
|
||||
/* "#utility.yul":328:345 */
|
||||
add
|
||||
/* "#utility.yul":319:325 */
|
||||
dup5
|
||||
/* "#utility.yul":275:346 */
|
||||
tag_10
|
||||
jump // in
|
||||
tag_15:
|
||||
/* "#utility.yul":229:353 */
|
||||
swap3
|
||||
swap2
|
||||
pop
|
||||
pop
|
||||
jump // out
|
||||
/* "#utility.yul":359:436 */
|
||||
tag_13:
|
||||
0x00
|
||||
/* "#utility.yul":425:430 */
|
||||
dup2
|
||||
/* "#utility.yul":414:430 */
|
||||
swap1
|
||||
pop
|
||||
/* "#utility.yul":404:436 */
|
||||
swap2
|
||||
swap1
|
||||
pop
|
||||
jump // out
|
||||
|
||||
auxdata: 0xa2646970667358221220a5874f19737ddd4c5d77ace1619e5160c67b3d4bedac75fce908fed32d98899864736f6c637827302e382e342d646576656c6f702e323032312e332e33302b636f6d6d69742e65613065363933380058
|
||||
}
|
||||
|
||||
Alternatively, the above output can also be obtained from `Remix <https://remix.ethereum.org/>`_,
|
||||
under the option "Compilation Details" after compiling a contract.
|
||||
|
||||
Notice that the ``asm`` output starts with the creation / constructor code. The deploy code is
|
||||
provided as part of the sub object (in the above example, it is part of the sub-object ``sub_0``).
|
||||
The ``auxdata`` field corresponds to the contract :ref:`metadata
|
||||
<encoding-of-the-metadata-hash-in-the-bytecode>`. The comments in the assembly output point to the
|
||||
source location. Note that ``#utility.yul`` is an internally generated file of utility functions
|
||||
that can be obtained using the flags ``--combined-json
|
||||
generated-sources,generated-sources-runtime``.
|
||||
|
||||
Similarly, the optimized assembly can be obtained with the command: ``solc --optimize --asm
|
||||
contract.sol``. Often times, it is interesting to see if two different sources in Solidity result in
|
||||
the same optimized code. For example, to see if the expressions ``(a * b) / c``, ``a * b / c``
|
||||
generates the same bytecode. This can be easily done by taking a ``diff`` of the corresponding
|
||||
assembly output, after potentially stripping comments that reference the source locations.
|
||||
|
||||
.. note::
|
||||
|
||||
The ``--asm`` output is not designed to be machine readable. Therefore, there may be breaking
|
||||
changes on the output between minor versions of solc.
|
||||
@ -127,6 +127,13 @@ Contents
|
||||
cheatsheet.rst
|
||||
grammar.rst
|
||||
|
||||
.. toctree::
|
||||
:maxdepth: 2
|
||||
:caption: Compiler
|
||||
|
||||
using-the-compiler.rst
|
||||
analysing-compilation-output.rst
|
||||
|
||||
.. toctree::
|
||||
:maxdepth: 2
|
||||
:caption: Internals
|
||||
@ -152,7 +159,6 @@ Contents
|
||||
security-considerations.rst
|
||||
smtchecker.rst
|
||||
resources.rst
|
||||
using-the-compiler.rst
|
||||
yul.rst
|
||||
style-guide.rst
|
||||
common-patterns.rst
|
||||
|
||||
Loading…
Reference in New Issue
Block a user