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what is a virtual computer? Why is it so vital on the planet of blockchain?
Hashgard Labs, a research institute of Hashgard, and BKFUND research Institute jointly performed an in-depth evaluation of virtual machines and wrote a research record about it.
(To examine the primary record, please check with Weibo account @Hashgard)
This time, we once once more interpreted the virtual desktop and chosen 4 consultant projects to behavior research and evaluation on their virtual machines.
A consultant venture of Blockchain — Ethereum (Etherum’s digital desktop) Ethereum digital computing device builds a stack-primarily based virtual operating environment, defines a collection of environments which are isolated from the node’s personal environment, shields the underlying changes of each node, and achieves the equal result (choice) of distinct nodes executing contracts. it's a 256-bit virtual computing device with a “quasi-turing complete”.
in line with the a lot of characteristics, the virtual desktop mode continues to be a relatively protected technical route within the wise contract technology, and is at present adopted via most blockchain techniques including Ethereum.
however, in terms of specific implementation, EVM at the moment generally believes that there are some design shortcomings, together with the following:
1) 256-bit note length. When the use of the lengths of eight, 16, 32, 64 supported with the aid of the present mainstream CPU, the CPU can at once supply native assist, and the software effectivity is excessive. although, the EVM makes use of a be aware length of 256 bits, and the processor requires additional operations to process at all times, so the computational efficiency is low. on the same time, compared with the mainstream word length, 256 bits will also have a certain storage waste, with a view to affect the consumption of gasoline. At present, some tests show that after the word length is changed to 64-bit or 128-bit, the running effectivity of the contract code and the storage can charge (indicated via the fuel cost) are better.
2) Floating aspect numbers don't seem to be supported and regular libraries are missing. This concern doesn't guide floating aspect. And as outlined above, the Solidity language, which is often used at the side of EVM, is additionally more prominent as a result of the inability of a native normal library. The emergence of OpenZeppelin has eased this problem. The writing framework of ERC20 and ERC721 makes building effortless. but there are all the time dangers linked to counting on third-celebration code bases. for example, there are many ERC20 certified Contracts that use OpenZeppelin some time ago because of the return cost of the characteristic, which could lead to unpredictable transfer results.
three) The contract code can not be modified and upgraded. seeing that the EVM does not use the commonplace von Neumann constitution, the application code is stored in a separate virtual ROM, rather than the vicinity of the code area in the well-known laptop reminiscence. In conception, the contract can also be upgraded by redeploying the contract. for this reason, when there are bugs and so on within the contract, it cannot be remedied through patching.
EVM is not Turing finished
The Turing laptop is a mathematical mannequin proposed with the aid of Aaron Turing in 1936. The Turing machine consists of an infinitely long strip of paper, a personality desk, a study/write head, a standing register, and a finite set of guidelines. in the beginning of the operation, the Turing desktop read/write head starts from a certain position according to the configuration in the intervening time (present position and existing grid content material, and so forth.), and the operation is carried out grade by grade with the guide set except the state becomes stopped, and the operation ends. in the field of computing, all the issues we look at are computational complications, and with Turing completeness, any computational difficulty can be solved. The essence of a programming language or virtual computer is a Turing machine. A programming language or virtual desktop is Turing-comprehensive. It ability that it might probably do all the things that Turing can do, that's, fixing all of the computational complications.
in the design of the Ethereum virtual laptop, considering that the calculation of the instruction is restrained by way of fuel, this limits the number of calculations that can be achieved. here's also a typical explanation for Turing incompleteness, since the bounded, recursive, or computational bounds trigger the application to terminate, so the programs that may run on the EVM are subject to many restrictions, and the EVM isn't Turing-finished.
Irrational design of EVM
1. smart contract design
Lack of average library aid: EVM lacks complete standard library assist, and even essentially the most simple string category guide. It is awfully hard in EVM. as an example, string splicing, cutting, browsing, all should be implemented by using builders themselves. The final result is that developers should pay consideration to greater fragmented particulars of their personal enterprise, in its place of specializing in their own enterprise construction. on the identical time, the self-carried out type library can be too excessive in time and area complexity, devour a lot of unnecessary gasoline, or the developer borrows principal type library code from the open supply venture, however it will introduce more protection concerns, aggravating The complexity of contract code auditing isn't price it.
elaborate to debug and look at various: EVM is intricate to debug and look at various. moreover throwing OutOfGas exceptions, EVM does not return any suggestions to the developer. it is inconceivable to print logs, make breakpoints, and debug single step. although the experience mechanism can partly enhance the problem, design of the adventure mechanism itself determines that it is not a sublime and straightforward debugging device.
Floating factor numbers are not supported: EVM does not guide floating point numbers. Ethereum makes use of Wei because the smallest unit. It best has integers and does not help different granularity size. This design avoids the precision problem brought about through the introduction of floating point numbers, but in exact development, builders as a way to represent an eth variable, there will be loads of zeros after the variable, which makes the code protection extremely advanced. at the same time, it is indisputable that floating-aspect numbers still have superb price in definite eventualities, and that they can't be deserted without delay.
Contracts cannot be upgraded: EVM does not support contract enhancements. Contract upgrades are a robust requirement in sensible contract construction. they're additionally concerns that every contract developer need to trust. Contract upgrades can put into effect protection patches for latest contracts and lengthen the aspects of present contracts. EVM doesn't assist enhancements in any respect, and developers can most effective solve this issue by issuing new contracts, which is time consuming and laborious.
2. sensible contract security
Overflow assault, EVM’s safeMath library is not used by means of default. for example, when the developer calculates the solidity uint256, if the ultimate result is enhanced than the maximum cost of uint256, the overflow will develop into a small number, consequently creating an overflow vulnerability. . connected tokens such as BEC and SMT have suffered from overflow attacks, which have brought extremely serious consequences. The BEC overflow vulnerability is as follows:
Re-entry assaults, an incredible function of solidity is that you should name other external contracts, however in the event you send eth to an external tackle or name an exterior contract, you deserve to post an external call. If the exterior address is a malicious contract, the attacker can add malicious code to the Fallback characteristic. When the transfer occurs, the Fallback function is known as to execute the malicious code. The malicious code executes the vulnerable feature of the calling contract, inflicting the transfer to be resubmitted. probably the most critical re-entry attacks happened in the early days of Ethereum, normal as the DAO vulnerability. right here contract fragment above all addresses the reentry attack:
unexpected characteristic execution, EVM doesn't strictly determine function calls, and if the contract handle is controllable as an incoming parameter, it can cause sudden conduct. details are as follows:
EVM has many problems at the design and security level. although the EVM group has developed a new contract development language equivalent to Vyper, it has been within the experimental stage and cannot be actually used.
The Ethereum virtual machine in response to WebAssembly does not have much growth in mathematical calculations. for this reason, if best the operation of transferring funds such as ERC20 is implemented, it may be a ways more desirable than other technical transformations, similar to consensus mechanism and fragmentation. more obtrusive
although, when implementing more complicated contract common sense reminiscent of sorting, WebAssembly will show a strong efficiency skills, which could supply superior technical support for blockchain enterprise purposes in complicated situations.
because of the above shortcomings, after ETF EVM, many blockchain tasks implement digital machines from lots of technical directions. we will additional divide into right here categories in line with the features of the technical implementation. it should be referred to that at current, many public chains handiest put up their development plans, and there's no precise digital desktop software code that can be run. The actual implementation may also alternate with the development of the project.
1. enrich EVM
despite the above shortcomings of EVM, many blockchain methods are nonetheless designed and carried out the use of EVM improvements. during this approach, the characteristic of the normal Ethereum can be reused to reduce the construction workload; on the other hand, the existing Ethereum ecology may also be utilized for swift building.
besides the fact that children some public-chain platforms equivalent to EOS have surpassed the Ethereum in terms of person activity, the lengthy-term ecological ambiance of Ethereum is an important ingredient for a new-born public chain to agree with in future construction and operation. factor. like the Hyperledger, which is the leading alliance chain platform, the Burrow venture is built with the Ethereum wise contract blockchain node with authorization administration, and is appropriate with the Ether equity Solidity development ecosystem with Cosmos’s Tendermint consensus engine.
in this ambiance, many public chains are designed to put in force digital machines, and they're implemented in an superior means in accordance with EVM.
for instance, the CKB of Layer 1 within the Nervos public-chain platform uses RISC-V as the instruction set to implement CKB-EVM. in the course of the RISC-V toolchain, CKB-EVM can guide any programming language for wise contract building.
Aion’s FastVM is designed with a 128-bit word length and makes use of the LLVM JIT as the working engine on the backside to enrich storage effectivity and speed. Aion’s digital machines additionally plan to aid dissimilar be aware lengths from 128 to 64 and 32 in the future to accommodate more utility eventualities and business needs.
it may even be optimized from the running technique of the virtual computing device. for the reason that Ethereum requires that each full node run the identical virtual laptop calculation and verify the consequences earlier than updating the ledger, this strategy undoubtedly influences performance. Some blockchain systems have more desirable this. for example, Zilliqa uses facts stream graphs to calculate slices to enhance concurrency.
2. suitable with natural guideline sets
Some blockchain methods implement the contract engine thought to be compatible with natural desktop instruction set innovations.
One of these is to use ordinary digital machine technology directly as a contract engine, however some modifications are obligatory to technically clear up deterministic issues. as an instance, R3 Corda makes use of the JVM as its sensible contract execution environment, ie the transaction forms in Corda are described and completed using the JVM’s bytecode. although, on account that there are nonetheless some non-deterministic operations within the traditional JVM, akin to random numbers, rubbish assortment in Java, and so on., Corda is at present attempting to improve a deterministic JVM sandbox atmosphere (DJVM for short). To observe if the code developed by using the person is non-deterministic.
The idea of this method is that the JVM has some merits over the EVM implementation of the smart contract engine:
1) The JVM has gone through colossal-scale, long-term industrial inspections. As a bottom layer, it's extra relaxed and powerful than EVM.
2) using the Java language and the current construction ecosystem, developers can get begun faster
three) Some language facets, including guide for floating aspect numbers, will even have benefits over Solidity.
The disadvantage is that the JVM has many features that are impartial of the blockchain necessities, and it is not easy to increase the fuel mechanism within the flow-via financial system to obtain termination.
in addition to average virtual machine know-how, some use emulators to simulate the typical instruction runtime environment, help multi-language construction and allow inventory code emigrate to the blockchain building atmosphere as least expensive as viable. as an instance, Qtum’s x86 virtual laptop is designed to be suitable with the ordinary x86 server instruction set, which permits the industry to build up a large amount of code for a very long time in a wise contract-based mostly blockchain execution ambiance. supply multi-language help.
3. wasm system
WebAssembly know-how is more and more being used to implement wise contract engines.
in the blockchain field, there are also some systems which have begun to make use of WebAssembly technology, which is additionally a favored style within the fresh sensible contract implementation technology. as an example, EOSIO has adopted WebAssembly to put in force its digital computer WAVM.
in comparison with the EVM of Ethereum, the virtual desktop the usage of WebAssembly technology has the following benefits:
1) Can guide C, C++, Rust and other multi-language building, cutting back the entry barrier and studying charge of builders
2) The effect of compiling into wasm is clear to the CPU architecture. although it can not run on the CPU, it will also be deployed and run in mainstream up to date browsers.
3) WebAssembly because the build formula is as shut as possible to the computing device code, the compilation quantity is small, the loading speed is quick, and the performance is comparatively excessive.
although, WebAssembly additionally has some shortcomings to be improved. as an instance, as an underlying know-how, WebAssembly is not mature satisfactory. for example, there are some compatibility concerns between new and historical browsers; quite a lot of points of ecological equipment have yet to be developed.
besides the fact that children, Ethereum is already in view that imposing EVM in WebAssembly, ie eWASM. within the latest Parity Ethereum node using Rust, the WebAssembly formulation can be used to put into effect its digital computer.
2. NEO VM
Neo sensible contract varieties encompass: verification contracts, characteristic contracts, and utility contracts.
sensible contract trigger
NEO’s sensible contracts have two triggers:
1. Authentication of the contract person: The wise contract acts as a contract account and triggers the wise contract when the consumer makes use of an asset within the contract account.
2. Manually ship a transaction to name a smart contract: The user sends a transaction (Invocation Transaction) to set off the execution of a smart contract.
A contract can also be brought on via each of the above strategies. considering the contract triggered by the authentication is the authentication manner of the UTXO model, it's completed before the transaction is written to the block. If the contract returns false or an exception occurs, the transaction usually are not written to the block.
The contract brought on via the transaction call is called when the transaction is written to the block. at the moment, even with the utility contract return and whether it fails, the transaction has already passed off and cannot affect the UTXO asset reputation within the transaction.
The figure above is the device structure diagram of NEO digital computing device (NeoVM). This photo describes the working principle of sensible contract. This photo comprises three components:
1. smart Contract Compiler (Compiler)
2. virtual computer Execution and Calculation Engine (AVM)
3. Interoperable layer of the virtual computer (interop carrier)
The deployment within the dotted field is the core of the virtual desktop. NeoVM carries three vital accessories: the execution engine, the stack, and the interoperability capabilities.
The eco-friendly on the left is the digital desktop execution engine (equivalent to the CPU), which can execute usual instructions, corresponding to circulation handle, stack operations, bit operations, arithmetic operations, logic operations, cryptography methods, and so forth., and might also be known as through system calls. The interoperable service layer interacts.
The core grey half is the digital machine’s computing stack (such as reminiscence). today, there are two implementations of digital machines, stack-based and register-primarily based. These two implementations have their personal advantages and drawbacks, and they all have iconic points. product. Stack-primarily based digital machines, including JVM, CPython, and .internet CLR. Register-primarily based, there are Dalvik and A stack-based virtual computing device has a concept of a compute stack, and the digital desktop interacts directly with the assessment Stack when performing precise operations.
when you consider that the execution defaults to fetching records from the operand stack, there is no deserve to specify an operand. for example, x86 assembles “ADD EAX, EBX”, you need to specify the place the operation should take the operand, and the place the influence is kept. despite the fact, the guidance of the stack-based digital laptop needn't be unique. as an instance, the addition operation is an easy “Add”, because the default operand is stored on the operand stack, and two information are popped at once from the operand stack. Addition, the result of the operation is saved at the desirable of the stack via default.
Interoperable provider layer
The blue half on the correct is the virtual machine’s interoperable provider layer (akin to peripherals). presently, the interoperable provider layer provides APIs for wise contractes to access blockchain statistics. These APIs provide access to block counsel, transaction advice, contract guidance, asset assistance, and more.
moreover this, the interoperable carrier layer gives a persistent storage area for each and every contract. every smart contract of NEO is optionally enabled with a non-public storage enviornment. The storage area is in the form of key-price. The NEO smart contract will depend on the callee of the contract to persist the context of the storage enviornment instead of the caller. To come to a decision. Of route, after the caller needs to move his storage context to the callee (ie, comprehensive the authorization), the callee can function study and write operations.
NEO smart Contracts are subject to a certain price for deployment or execution, divided into deployment and execution prices.
The deployment cost capacity that the developer can pay a definite charge to the blockchain equipment when deploying a sensible contract to the blockchain. according to the necessary services of the contract, the system will cost one hundred~one thousand gas and use it as device profits.
Execution fees suggest that every execution of a wise contract will pay a undeniable execution charge to the NEO device.
three. EOS VM
The EOS VM adopts the WASM (WebAssembly)-LLVM (Low degree virtual desktop) structure. The backside layer of the EOS digital laptop consists of LLVM and WebAssembly. they're all capable-made, LLVM has long been used for object-C, and webAssembly is used. The implementation of the front conclusion of the web web page. Wasm is at present exceptionally utilized in internet purposes, and EOS makes use of it as the final structure of sensible contracts. The mechanism is not the identical as the current browser working and calling.
EOS sensible Contract abstract:
The wise contract acts as an software registered in the EOS blockchain and runs on the EOS node. sensible contracts outline connected interfaces that contain actions, records buildings, and linked parameters. The smart contract implements these interfaces, is compiled right into a binary file of the wasm suffix, and performed. For the blockchain, the last shop is a sensible contract transaction.
a wise contract contains an action and a sort definition: motion: defines and implements the habits and performance of a wise contract. category definition: defines the content and data constitution required by using the contract.
The client sends a message to set off the execution of the action, and the closing storage variety of the smart contract is transaction. A transaction can include diverse actions, including as a minimum one motion.
An illustration of a wise contract definition:
#outline EOSIO_API( type, members ) \ BOOST_PP_SEQ_FOR_EACH( EOSIO_API_CALL, class, participants )
extend the protected macros:
#outline EOSIO_API_CALL( r, OP, elem ) \ case ::eosio::string_to_name( BOOST_PP_STRINGIZE(elem) ): \ eosio::execute_action( &thiscontract, &OP::elem ); \ spoil;
This completes the implementation of the name from the contract to the underlying route.
Contract compilation system and digital computer:
The clever contract compilation system is as follows:
1. Use clang to target wasm32 and generate intermediate file bc
2. Generate a file through the use of the LLVM-link link to generate a bc file and a standard library bc file.
three. Use LLVM’s llc to generate s meeting files id="e75f" class="jn jo gf bs jp b jq jr js jt ju jv jw jx jy jz ka">four. apply the eosio-s2wasm device to convert the s file to a wast file
5. observe the eosio-wast2wasm device to transform the wast file to the remaining wast file
Why no longer use clan as a substitute of wasm, I suppose it may be as a result of the proven fact that wasm represents the longer term style, and there are more clarification containers for wasm support in the future, which is handy for getting access to numerous virtual machines.
WASM virtual computer:
In EOS, modules reminiscent of WASM that use current services are centralized within the library directory, which can be compiled one at a time and then inherited.
The WASM digital machine is principally discovered under the wasm-jit below the libraries.
1. libraries/chain: particularly defines virtual laptop related interfaces
2. libraries/wasm-jit: peculiarly the implementation of wise contracts. also in the contracts directory, there's ABI’s auxiliary code.
The source code of the wasm-jit digital desktop is: ~/eos/libraries/wasm-jit/source, the main folder: Emscripten, IR, Runtime, courses, WASM, WAST
1. IR: IR is step one of excessive-level language to computing device language, adopted by WAST parsing, WASM serialization processing, — — in keeping with Runtime processing.
2. Emscripten: a tool for changing high-stage languages to LLVM bytecode
three. Runtime execution engine: contains execution bytecode (laptop code), external call, translate bytecode to IR, generate computer code, and so forth.
4. WASM: WASM 的 LICENSE
5. WAST: Parse parsing function modules different:
6. Logging: Log administration
7. platforms: similar to distinctive systems
Wasm-jit is an independent digital machine in EOS. The explanation why WASM is used is since it makes use of intermediate language to translate high-degree language programs into IR (intermediate illustration) intermediate language and then assemble into machine language. WAVM can convert between changed into and wasm, wast is textual content, the use of near-desktop translation syntax, wasm is binary code
assemble id="7498" class="jn jo gf bs jp b jq jr js jt ju jv jw jx jy jz ka">Disassemble id="5494" class="jn jo gf bs jp b jq jr js jt ju jv jw jx jy jz ka">The supply code of the wasm-jit virtual computer is: ~/eos/libraries/wasm-jit/source, the directory constitution is as follows:
leading folders：Emscripten, IR，Runtime, classes,WASM, WAST
IR: IR is step one in high-level language to laptop language, adopted by means of WAST parsing, WASM serialization, and Runtime processing.
Emscripten: a tool for changing high-degree languages to LLVM bytecode
Runtime execution engine: contains execution bytecode (computer code), external name, translate bytecode to IR, generate computing device code, etc.
WASM: WASM 的 LICENSE
WAST: Parse parsing function module
other: Logging: Log administration platforms: similar to distinct structures
Irrational design of EOS
there's a separate set of intelligent contract engine based on WebAssembly, however the present EOS contract construction has here obtrusive problems:
1. The account equipment is not friendly: it is tricky to create an account. After developing an account, the contract can be issued. EOS needs to use an existing account to create a new account. looking for a pal or third celebration with an EOS account isn't a problem for anybody. It’s handy. To create an account, you deserve to purchase RAM, which ability you deserve to spend funds to build an account. if you find a third birthday party to assist create an account, there's a economic risk. After growing an account, you need to personal loan EOS in alternate for CPU usage time and web bandwidth to function on the EOS community. These operations are too cumbersome for builders.
2. RAM price: RAM is expensive, the contract operation should use RAM, EOS opens the RAM marketplace for trading memory, although RAM may also be purchased and sold, however there are still many people hypothesis, leading to RAM high priced.
3. development is problematic: the use of C++ as the contract development language significantly improves the contract building threshold. C++ itself is extraordinarily complicated, and it additionally must name C++ API to complete sensible contract development, for developers. The skill is extraordinarily excessive.
hence, in the face of a lot of enumerated issues, EOS smart contract development is not very captivating to builders, and might even be the cause of builders to surrender EOS.
four. IOST VM
starting aspect: in response to V8’s astounding efficiency on NodeJs and Chrome
IOST V8VM structure and design
The core of the V8VM structure is VMManger, which has right here three services:
1. VM entry, request to obtain other modules externally, including RPC request, block verification, Tx verification, and so forth., pre-processed, formatted and handed over to VMWorker for execution.
3. manipulate the interplay with the State database to make sure the atomicity of each IOST transaction, and to be able to roll returned the total transaction in the adventure of a contract execution error or insufficient gas. on the equal time in the State database, it also implements a two-level reminiscence cache, and eventually should be flushed to RocksDB.
Sandbox core design
chiefly for contract building and winding, there are two main services:
in particular for the true implementation of the chain contract, there are two main capabilities: