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Update assembly for 0.6.0.
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chriseth
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@ -6,7 +6,8 @@ Solidity Assembly
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Solidity defines an assembly language that you can use without Solidity and also
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as "inline assembly" inside Solidity source code. This guide starts with describing
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how to use inline assembly, how it differs from standalone assembly, and
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how to use inline assembly, how it differs from standalone assembly
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(sometimes also referred to by its proper name "Yul"), and
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specifies assembly itself.
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.. _inline-assembly:
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@ -22,6 +23,10 @@ As the EVM is a stack machine, it is often hard to address the correct stack slo
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and provide arguments to opcodes at the correct point on the stack. Solidity's inline
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assembly helps you do this, and with other issues that arise when writing manual assembly.
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For inline assembly, the stack is actually not visible at all, but if you look
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closer, there is always a very direct translation from inline assembly to
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the stack based EVM opcode stream.
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Inline assembly has the following features:
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* functional-style opcodes: ``mul(1, add(2, 3))``
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@ -48,32 +53,22 @@ these curly braces, you can use the following (see the later sections for more d
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- literals, i.e. ``0x123``, ``42`` or ``"abc"`` (strings up to 32 characters)
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- opcodes in functional style, e.g. ``add(1, mload(0))``
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- variable declarations, e.g. ``let x := 7``, ``let x := add(y, 3)`` or ``let x`` (initial value of empty (0) is assigned)
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- variable declarations, e.g. ``let x := 7``, ``let x := add(y, 3)`` or ``let x`` (initial value of 0 is assigned)
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- identifiers (assembly-local variables and externals if used as inline assembly), e.g. ``add(3, x)``, ``sstore(x_slot, 2)``
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- assignments, e.g. ``x := add(y, 3)``
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- blocks where local variables are scoped inside, e.g. ``{ let x := 3 { let y := add(x, 1) } }``
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The following features are only available for standalone assembly:
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- direct stack control via ``dup1``, ``swap1``, ...
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- direct stack assignments (in "instruction style"), e.g. ``3 =: x``
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- labels, e.g. ``name:``
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- jump opcodes
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.. note::
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Standalone assembly is supported for backwards compatibility but is not documented
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here anymore.
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At the end of the ``assembly { ... }`` block, the stack must be balanced,
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unless you require it otherwise. If it is not balanced, the compiler generates
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a warning.
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Inline assembly manages local variables and control-flow. Because of that,
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opcodes that interfere with these features are not available. This includes
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the ``dup`` and ``swap`` instructions as well as ``jump`` instructions and labels.
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Example
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-------
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The following example provides library code to access the code of another contract and
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load it into a ``bytes`` variable. This is not possible with "plain Solidity" and the
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idea is that assembly libraries will be used to enhance the Solidity language.
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idea is that reusable assembly libraries can enhance the Solidity language
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without a compiler change.
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.. code::
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@ -157,26 +152,23 @@ Opcodes
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-------
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This document does not want to be a full description of the Ethereum virtual machine, but the
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following list can be used as a reference of its opcodes.
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following list can be used as a quick reference of its opcodes.
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If an opcode takes arguments (always from the top of the stack), they are given in parentheses.
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Note that the order of arguments can be seen to be reversed in non-functional style (explained below).
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Opcodes marked with ``-`` do not push an item onto the stack (do not return a result),
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those marked with ``*`` are special and all others push exactly one item onto the stack (their "return value").
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If an opcode takes arguments, they are given in parentheses.
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Opcodes marked with ``-`` do not return a result,
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those marked with ``*`` are special in a certain way and all others return exactly one value.
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Opcodes marked with ``F``, ``H``, ``B``, ``C`` or ``I`` are present since Frontier, Homestead,
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Byzantium, Constantinople or Istanbul, respectively.
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In the following, ``mem[a...b)`` signifies the bytes of memory starting at position ``a`` up to
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but not including position ``b`` and ``storage[p]`` signifies the storage contents at position ``p``.
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but not including position ``b`` and ``storage[p]`` signifies the storage contents at slot ``p``.
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The opcodes ``pushi`` and ``jumpdest`` cannot be used directly.
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In the grammar, opcodes are represented as pre-defined identifiers.
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In the grammar, opcodes are represented as pre-defined identifiers ("built-in functions").
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| Instruction | | | Explanation |
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+=========================+=====+===+=================================================================+
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| stop + `-` | F | stop execution, identical to return(0,0) |
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| stop() + `-` | F | stop execution, identical to return(0, 0) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| add(x, y) | | F | x + y |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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@ -208,11 +200,11 @@ In the grammar, opcodes are represented as pre-defined identifiers.
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| iszero(x) | | F | 1 if x == 0, 0 otherwise |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| and(x, y) | | F | bitwise and of x and y |
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| and(x, y) | | F | bitwise "and" of x and y |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| or(x, y) | | F | bitwise or of x and y |
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| or(x, y) | | F | bitwise "or" of x and y |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| xor(x, y) | | F | bitwise xor of x and y |
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| xor(x, y) | | F | bitwise "xor" of x and y |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| byte(n, x) | | F | nth byte of x, where the most significant byte is the 0th byte |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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@ -220,7 +212,7 @@ In the grammar, opcodes are represented as pre-defined identifiers.
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| shr(x, y) | | C | logical shift right y by x bits |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| sar(x, y) | | C | arithmetic shift right y by x bits |
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| sar(x, y) | | C | signed arithmetic shift right y by x bits |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| addmod(x, y, m) | | F | (x + y) % m with arbitrary precision arithmetic |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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@ -230,17 +222,9 @@ In the grammar, opcodes are represented as pre-defined identifiers.
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| keccak256(p, n) | | F | keccak(mem[p...(p+n))) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| jump(label) | `-` | F | jump to label / code position |
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| pc() | | F | current position in code |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| jumpi(label, cond) | `-` | F | jump to label if cond is nonzero |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| pc | | F | current position in code |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| pop(x) | `-` | F | remove the element pushed by x |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| dup1 ... dup16 | | F | copy nth stack slot to the top (counting from top) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| swap1 ... swap16 | `*` | F | swap topmost and nth stack slot below it |
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| pop(x) | `-` | F | discard value x |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| mload(p) | | F | mem[p...(p+32)) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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@ -252,27 +236,27 @@ In the grammar, opcodes are represented as pre-defined identifiers.
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| sstore(p, v) | `-` | F | storage[p] := v |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| msize | | F | size of memory, i.e. largest accessed memory index |
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| msize() | | F | size of memory, i.e. largest accessed memory index |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| gas | | F | gas still available to execution |
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| gas() | | F | gas still available to execution |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| address | | F | address of the current contract / execution context |
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| address() | | F | address of the current contract / execution context |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| balance(a) | | F | wei balance at address a |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| selfbalance() | | I | equivalent to balance(address()), but cheaper |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| caller | | F | call sender (excluding ``delegatecall``) |
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| caller() | | F | call sender (excluding ``delegatecall``) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| callvalue | | F | wei sent together with the current call |
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| callvalue() | | F | wei sent together with the current call |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| calldataload(p) | | F | call data starting from position p (32 bytes) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| calldatasize | | F | size of call data in bytes |
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| calldatasize() | | F | size of call data in bytes |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| calldatacopy(t, f, s) | `-` | F | copy s bytes from calldata at position f to mem at position t |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| codesize | | F | size of the code of the current contract / execution context |
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| codesize() | | F | size of the code of the current contract / execution context |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| codecopy(t, f, s) | `-` | F | copy s bytes from code at position f to mem at position t |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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@ -280,7 +264,7 @@ In the grammar, opcodes are represented as pre-defined identifiers.
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| extcodecopy(a, t, f, s) | `-` | F | like codecopy(t, f, s) but take code at address a |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| returndatasize | | B | size of the last returndata |
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| returndatasize() | | B | size of the last returndata |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| returndatacopy(t, f, s) | `-` | B | copy s bytes from returndata at position f to mem at position t |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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@ -315,7 +299,7 @@ In the grammar, opcodes are represented as pre-defined identifiers.
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| selfdestruct(a) | `-` | F | end execution, destroy current contract and send funds to a |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| invalid | `-` | F | end execution with invalid instruction |
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| invalid() | `-` | F | end execution with invalid instruction |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| log0(p, s) | `-` | F | log without topics and data mem[p...(p+s)) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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@ -328,23 +312,23 @@ In the grammar, opcodes are represented as pre-defined identifiers.
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| log4(p, s, t1, t2, t3, | `-` | F | log with topics t1, t2, t3, t4 and data mem[p...(p+s)) |
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| t4) | | | |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| chainid | | I | ID of the executing chain (EIP 1344) |
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| chainid() | | I | ID of the executing chain (EIP 1344) |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| origin | | F | transaction sender |
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| origin() | | F | transaction sender |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| gasprice | | F | gas price of the transaction |
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| gasprice() | | F | gas price of the transaction |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| blockhash(b) | | F | hash of block nr b - only for last 256 blocks excluding current |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| coinbase | | F | current mining beneficiary |
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| coinbase() | | F | current mining beneficiary |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| timestamp | | F | timestamp of the current block in seconds since the epoch |
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| timestamp() | | F | timestamp of the current block in seconds since the epoch |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| number | | F | current block number |
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| number() | | F | current block number |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| difficulty | | F | difficulty of the current block |
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| difficulty() | | F | difficulty of the current block |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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| gaslimit | | F | block gas limit of the current block |
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| gaslimit() | | F | block gas limit of the current block |
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+-------------------------+-----+---+-----------------------------------------------------------------+
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Literals
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@ -423,12 +407,6 @@ Local Solidity variables are available for assignments, for example:
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To clean signed types, you can use the ``signextend`` opcode:
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``assembly { signextend(<num_bytes_of_x_minus_one>, x) }``
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Labels
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------
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Support for labels has been removed in version 0.5.0 of Solidity.
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Please use functions, loops, if or switch statements instead.
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Declaring Assembly-Local Variables
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----------------------------------
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@ -574,8 +552,7 @@ opcode.
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Functions can be defined anywhere and are visible in the block they are
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declared in. Inside a function, you cannot access local variables
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defined outside of that function. There is no explicit ``return``
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statement.
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defined outside of that function.
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If you call a function that returns multiple values, you have to assign
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them to a tuple using ``a, b := f(x)`` or ``let a, b := f(x)``.
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