Add design proposal to embed Libra's Move (#5067)

* Add design proposal to embed Libra's Move

* Apply review feedback

* Pipeline VM -> the runtime
* defines -> define

book/src/SUMMARY.md

@@ -58,6 +58,7 @@
   - [Credit-only Accounts](credit-only-credit-debit-accounts.md)
   - [Validator](validator-proposal.md)
   - [Simple Payment and State Verification](simple-payment-and-state-verification.md)
+  - [Embedding the Move Langauge](embedding-move.md)
 
 - [Implemented Design Proposals](implemented-proposals.md)
   - [Blocktree](blocktree.md)

book/src/embedding-move.md

@@ -0,0 +1,66 @@
+# Embedding the Move Language
+
+## Problem
+
+Solana enables developers to write on-chain programs in general purpose
+programming languages such as C or Rust, but those programs contain
+Solana-specific mechanisms. For example, there isn't another chain that asks
+developers to create a Rust module with a `process_instruction(KeyedAccounts)`
+function. Whenever practical, Solana should offer dApp developers more portable
+options.
+
+Until just recently, no popular blockchain offered a language that could expose
+the value of Solana's massively parallel [runtime](runtime.md). Solidity
+contracts, for example, do not separate references to shared data from contract
+code, and therefore need to be executed serially to ensure deterministic
+behavior.  In practice we see that the most aggressively optimized EVM-based
+blockchains all seem to peak out around 1,200 TPS - a small fraction of what
+Solana can do. The Libra project, on the other hand, designed an on-chain
+programming language called Move that is more suitable for parallel execution.
+Like Solana's runtime, Move programs depend on accounts for all shared state.
+
+The biggest design difference between Solana's runtime and Libra's Move VM is
+how they manage safe invocations between modules.  Solana took an operating
+systems approach and Libra took the domain-specific language approach.  In the
+runtime, a module must trap back into the runtime to ensure the caller's module
+did not write to data owned by the callee. Likewise, when the callee completes,
+it must again trap back to the runtime to ensure the callee did not write to
+data owned by the caller. Move, on the other hand, includes an advanced type
+system that allows these checks to be run by its bytecode verifier. Because
+Move bytecode can be verified, the cost of verification is paid just once, at
+the time the module is loaded on-chain. In the runtime, the cost is paid each
+time a transaction crosses between modules. The difference is similar in spirit
+to the difference between a dynamically-typed language like Python versus a
+statically-typed language like Java. Solana's runtime allows dApps to be
+written in general purpose programming languages, but that comes with the cost
+of runtime checks when jumping between programs.
+
+This proposal attempts to define a way to embed the Move VM such that:
+
+* cross-module invocations within Move do not require the runtime's
+  cross-program runtime checks
+* Move programs can leverage functionality in other Solana programs and vice
+  versa
+* Solana's runtime parallelism is exposed to batches of Move and non-Move
+  transactions
+
+## Proposed Solution
+
+### Move VM as a Solana loader
+
+The Move VM shall be embedded as a Solana loader under the identifier
+`MOVE_PROGRAM_ID`, so that Move modules can be marked as `executable` with the
+VM as its `owner`. This will allow modules to load module dependencies, as well
+as allow for parallel execution of Move scripts.
+
+All data accounts owned by Move modules must set their owners to the loader,
+`MOVE_PROGRAM_ID`. Since Move modules encapsulate their account data in the
+same way Solana programs encapsulate theirs, the Move module owner should be
+embedded in the account data. The runtime will grant write access to the Move
+VM, and Move grants access to the module accounts.
+
+### Interacting with Solana programs
+
+To invoke instructions in non-Move programs, Solana would need to extend the
+Move VM with a `process_instruction()` system call. It would work the same as
+`process_instruction()` Rust BPF programs.