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| author | chriseth <c@ethdev.com> | 2017-02-23 01:57:31 +0800 |
|---|---|---|
| committer | chriseth <c@ethdev.com> | 2017-03-03 22:41:02 +0800 |
| commit | c85f9257f87bb8d6f84a4a74a9b290d7207eebd7 (patch) | |
| tree | e3c9261e89c300792a66baf01f2371013fd8be3a /docs | |
| parent | e963405a19c8435105df1fa48c9cdd92037b341f (diff) | |
| download | dexon-solidity-c85f9257f87bb8d6f84a4a74a9b290d7207eebd7.tar.gz dexon-solidity-c85f9257f87bb8d6f84a4a74a9b290d7207eebd7.tar.zst dexon-solidity-c85f9257f87bb8d6f84a4a74a9b290d7207eebd7.zip | |
Clarify stack height.
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/assembly.rst | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/docs/assembly.rst b/docs/assembly.rst index b28216f1..cc2ad1c4 100644 --- a/docs/assembly.rst +++ b/docs/assembly.rst @@ -333,11 +333,12 @@ push their entry label (with virtual function resolution applied). The calling s in solidity are: - the caller pushes return label, arg1, arg2, ..., argn - - the call returns with ret1, ret2, ..., retn + - the call returns with ret1, ret2, ..., retm This feature is still a bit cumbersome to use, because the stack offset essentially changes during the call, and thus references to local variables will be wrong. -It is planned that the stack height changes can be specified in inline assembly. +The assumed stack height can be changed by using labels: ``funreturn[-2]:`` +The number in brackets should be `m - n - 1`. .. code:: @@ -939,8 +940,16 @@ Pseudocode:: Opcode Stream Generation ------------------------ -During opcode stream generation, we keep track of the current stack height, -so that accessing stack variables by name is possible. +During opcode stream generation, we keep track of the current stack height +in a counter, +so that accessing stack variables by name is possible. The stack height is modified with every opcode +that modifies the stack and with every label that is annotated with a stack +adjustment. Every time a new +local variable is introduced, it is registered together with the current +stack height. If a variable is accessed (either for copying its value or for +assignment), the appropriate DUP or SWAP instruction is selected depending +on the difference bitween the current stack height and the +stack height at the point the variable was introduced. Pseudocode:: @@ -980,7 +989,7 @@ Pseudocode:: POP LabelDefinition(name [id1, ..., idn] :) -> JUMPDEST - // register new variables id1, ..., idn and adjust the assumed stack + // register new local variables id1, ..., idn and adjust the stack // height such that it matches the stack height at the beginning of // the block plus all local variables including the just registered // ones where idn is at the stack top. If n is zero, resets the stack |