The core of the system is the VM
EVM, growing pains
- 256 bit words
- It has instuctions that shoudn't be instuctions (GASLIMIT, BALANCE, SHA3, etc)
- Missing instuctions like shift and rotate
- No system call equivalent
- Its a hard compilation target for many HLL
- Largely incompatible with the ecosystems outside of Ethereum
Can there be a better way?
What is WebAssembly?
WebAssembly or wasm is a new, portable, size- and load-time-efficient binary format that aims to execute at native speed by taking advantage of common hardware capabilities available on a wide range of platforms.
What is WebAssembly?
- Fast & Efficient
- Secure Sandbox
- Toolchain Compatibility
- Extensible
- The Combined Powers of the Web!
W3C Working Group
www.w3.org/community/webassembly
- Participants (660)
- Mozilla
- Microsoft
- Apple
Instruction Set and AST
- RISC like
- Integer and float operations
- Defined as an AST
- can be easily processed
- can be easily transformed
- can be interpreted with a Stack Machine
- or JITed
S-Expressions
(module (import $useGas "ethereum" "useGas" (param i32)) (memory 1) (export "memory" memory) (export "main" $main) (func $main (local $sp i32) (local $jump_dest i32) (set_local $sp (i32.const -32)) (set_local $jump_dest (i32.const -1)) (loop $done $loop (block $1 (block $0 (br_table $0 (if (i32.eq (get_local $jump_dest) (i32.const -1)) (then (i32.const 0)) (else (unreachable))))) (call_import $useGas (i32.const 6)) (if (i32.gt_s (get_local $sp) (i32.const 32672)) (then (unreachable))) (call $PUSH (i64.const 0) (i64.const 0) (i64.const 0) (i64.const 96) (get_local $sp)) (set_local $sp (i32.add (get_local $sp) (i32.const 32))) (call $PUSH (i64.const 0) (i64.const 0) (i64.const 0) (i64.const 0) (get_local $sp)) (set_local $sp (i32.add (get_local $sp) (i32.const 32)))))))
Semantics
(i64.const 42)- Types
- i32
(i32.const 0xffffffff) - i64
(i64.const -644)
- i32
- `(local $a)`
- Memory Access
(i64.load (i64.const 4))(i64.store (get_local $a) (i64.const 4))
- Arithmetic
- Conditionals
-
Calls
(call_import $useGas (i64.const 33))
Binary Dump
0061736d0b00000004747970651003400101004005020202020
10040000006696d706f727412010008657468657265756d0675
73654761730866756e6374696f6e03020102066d656d6f72790
3010101066578706f7274070101046d61696e04636f64655f02
01005b01020110601500107f15010201011401107f4d0310000
40a0f080000000000000f1006180100140010a0ff0153030a0f
11001100110011e000140016050014001020401500110011001
10011001400160500140010204015000f0f
Binary Disected
0000000: 0061 736d ; WASM_BINARY_MAGIC 0000004: 0b00 0000 ; WASM_BINARY_VERSION ; section "type" 0000008: 04 ; string length 0000009: 7479 7065 ; section id: "type" 000000d: 00 ; section size (guess) 000000e: 01 ; num types ; type 0 000000f: 40 ; function form 0000010: 02 ; num params 0000011: 01 ; param type 0000012: 01 ; param type 0000013: 01 ; num results 0000014: 01 ; result_type ; section "function" 0000015: 08 ; string length 0000016: 6675 6e63 7469 6f6e ; section id: "function" 000001e: 00 ; section size (guess) 000001f: 01 ; num functions 0000020: 00 ; function 0 signature index 000001e: 02 ; FIXUP section size ; section "export" 0000021: 06 ; string length 0000022: 6578 706f 7274 ; section id: "export" 0000028: 00 ; section size (guess) 0000029: 01 ; num exports 000002a: 00 ; export func index 000002b: 06 ; string length 000002c: 6164 6454 776f ; export name ; section "code" 0000032: 04 ; string length 0000033: 636f 6465 ; section id: "code" 0000037: 00 ; section size (guess) 0000038: 01 ; num functions ; function body 0 0000039: 00 ; func body size (guess) 000003a: 00 ; local decl count 000003b: 14 ; OPCODE_GET_LOCAL
Binary Encoding
- Fast decoding
- Single pass validation
- Extensible
Availability of VMs
- Chrome (chrome://flags - enable-webassembly)
- Firefox Nightly (about:config and set `javascript.options.wasm` to true)
- Microsoft Edge
- node.js 7.0-pre (--enable-wasm)
- wasm-jit-prototype (github.com/WebAssembly/wasm-jit-prototype)
- Ocaml "the spec" (github.com/WebAssembly/spec)
- interpreters
- sexpr-wasm-prototypen (github.com/WebAssembly/sexpr-wasm-prototype)
- binaryen (github.com/WebAssembly/binaryen)
Ethereum flavored WebAssembly e^WASM
- A proposed replacement for EVM
- A restricted subset of WebAssembly
- No floating point operations
- Defines Backwards Compatibility
- Defines Metering
- Defines an interface for interacting with the Ethereum Blockchain
EVM2WASM
- Transcompiles EVM code to WebAssembly
- Can be run as a contract
- Compliant with the offical EVM tests
- Produces very fast EVM code
- ~5000 line of wasm
- ~400 line of js
EVM2WASM
Metering Injection
Metering is decoupled from the VM
st=>start: raw wasm
e=>end: run
op=>operation: Validate
op2=>operation: Injection Metering
cond=>condition: Yes or No?
st->op->op2->e
Metering By Branch
Metering By Branch
Interfaces
Glueing all this together
eWASM Ethereum Interface (EEI)
Defines the Ethereum blockchain methods for contracts:
- getCallDataSize ~ CALLDATASIZE
- callDataCopy ~ CALLDATACOPY
- storageLoad ~ SLOAD
- storageStore ~ SSTORE
- call ~ CALL
- delegateCall ~ DELEGATECALL
- return ~ RETURN
- …
A total of 29 methods.
Example: storageLoad
(call_import $storageLoad (i32.const 0) (i32.const 32))
;; ^ key offset in memory
;; ^ result offset in memory
Simples.
eWASM Contract Interface (ECI)
Defines the format of contracts:
- WebAssembly binary encoding version 0xb
- Single entry point: main
- Sets other limitations.
Example contract
Drumroll:
(module
(memory 1
(segment 0 "Hello World!")
)
(import $return "ethereum" "return" (param i32 i32))
(export "main" $main)
(func $main
(call_import $return (i32.const 0) (i32.const 12))
)
)
System Contracts
-
Sentinel
- ECI validation
- metering injection
- wrap into deployer
-
evm2wasm!
-
EVM1 precompiled contracts
VM Semantics
Only 3 new rules for a client:
-
Check contract code for eWASM signature
-
Use evm2wasm to transcompile if needed
-
Use sentinel contract during contract creation
ewasm-kernel and Hera
-
ewasm-kernel
- Javascript
- runs in browsers and node.js
- < 1000 lines for the interface and VM core
-
Hera
- C++
- EVM-C compatible
- works with cpp-ethereum (eth –vm hera)
- and pyethereum \o/
- … and hopefully go-ethereum + parity in the future
The test network
Programming in C and the precompiles
clang & ewasm-libc
Example: sha256
#include "ethereum.h"
#define BASE_FEE 60
#define WORD_FEE 12
void main() {
size_t datasize = ethereum_calldatasize();
unsigned char data[datasize];
unsigned char ret[32] = { 0 };
ethereum_calldatacopy(data, 0, datasize);
ethereum_usegas(BASE_FEE + (((datasize + 31) / 32) * WORD_FEE));
mbedtls_sha256(data, datasize, ret, 0);
ethereum_return(ret, 32);
}
Solidity for eWASM
Input:
contract A {
function a() {
throw;
}
function b() payable returns (uint64) {
uint64 x = 42;
return x;
}
}
Solidity for eWASM
Output:
;; Contract: A
(module
(import $callDataCopy "ethereum" "callDataCopy" (param i32 i32 i32))
(import $getCallValue "ethereum" "getCallValue" (param i32))
(import $return "ethereum" "return" (param i32))
(memory 1 1)
(export "memory" memory)
(export "main" $main)
(func $main
(call_import $callDataCopy (i32.const 0) (i32.const 0) (i32.const 4))
(call $dispatcher (i32.load (i32.const 0)))
(unreachable)
)
(func $ensureNotPayable
(call_import $getCallValue (i32.const 0))
(if (i64.ne (i64.const 0) (i64.load (i32.const 0)) (unreachable))
(if (i64.ne (i64.const 0) (i64.load (i32.const 8)) (unreachable))
)
(func $dispatcher
(param $sig i32)
(if (i32.eq (get_local $sig) (i32.const 0x0dbe671f)) (then (call $__0dbe671f)))
(if (i32.eq (get_local $sig) (i32.const 0x4df7e3d0)) (then (call $__4df7e3d0)))
(unreachable)
)
;; function: a()
(func $__0dbe671f
(call $ensureNotPayable)
(block
(unreachable)
)
)
;; function: b() payable
(func $__4df7e3d0
(block
(local $x (param i64))
(set_local $x (i64.const 42))
(i64.store (i32.const 0) (i64.const 0))
(i64.store (i32.const 8) (i64.const 0))
(i64.store (i32.const 16) (i64.const 0))
(i64.store (i32.const 24) (get_local $x))
(call_import $return (i32.const 0) (i32.const 32))
)
)
)
Bonus: Gas Cost Calculation
-
Gas cost is based on the cycle count of the instructions.
-
The gas cost table is stored in a contract.
-
SHA256 performance (of 8kb data):
- precompile cost: ~3 100
- eWASM cost: ~6 500
- EVM (Solidity) cost: ~32 000 000
- EVM (Solidity) cost (with shifts): ~1 000 000
(call_import $ethereumReturn)
See more awesome details at https://github.com/ewasm
Error: Out-Of-Gas!
Ethereum ❤️ WebAssembly Martin Becze github.com/wanderer Alex Beregszaszi github.com/axic
{"metaMigratedAt":"2023-06-14T11:52:28.497Z","metaMigratedFrom":"Content","title":"Ethereum","breaks":true,"contributors":"[]"}