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fix: remove atomic instruction #443

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fix: remove atomic instruction #443

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10 changes: 4 additions & 6 deletions rfcs/0049-ckb-vm-version-2/0049-ckb-vm-version-2.md
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Expand Up @@ -19,7 +19,6 @@ The upgrade of CKB-VM in 2023 aims to enhance the security, portability, and eff
- We currently lack a secure and straightforward method to invoke one script from another.
- The **[dynamic library call](https://github.com/nervosnetwork/rfcs/blob/master/rfcs/0009-vm-syscalls/0009-vm-syscalls.md#load-cell-data-as-code)** presents a security concern. The sub-script and parent script share the same memory space, leading to an uncontrolled security risk when calling an unknown sub-script.
- Although the **[Exec](https://github.com/nervosnetwork/rfcs/blob/master/rfcs/0034-vm-syscalls-2/0034-vm-syscalls-2.md#exec)** system call doesn't pose any security issues, it is exceptionally challenging to utilize effectively.
- Compilation of third-party libraries frequently encounters failures caused by the absence of atomic instructions. This issue arises because Rust solely offers the rv64imac target.
- Running more intricate scripts (such as zero-knowledge proofs) on CKB-VM necessitates higher performance requirements for CKB-VM.

## **Specification**
Expand All @@ -28,11 +27,10 @@ To address the aforementioned issues, we have implemented the following optimiza

In comparison to version 1, version 2 of CKB-VM incorporates the following enhancements:

1. One notable addition is the inclusion of a new system call called "Spawn," which can be further explored in the RFC titled "VM Syscalls 3." In essence, Spawn serves as an alternative to dynamic library calls and Exec. With Spawn, it becomes possible to specify the memory size for spawned scripts during initialization. This capability ensures that each workload can access the necessary resources without squandering them on unused memory.
2. We have taken the initiative to implement a standard extension in the form of the [RISC-V "A" Standard Extension for Atomic Instructions, Version 2.1](https://five-embeddev.com/riscv-isa-manual/latest/a.html). This implementation is particularly valuable for facilitating code porting, as certain third-party libraries may rely on atomic instructions. By incorporating this extension into CKB-VM, we enhance its compatibility with such libraries and foster smoother transitions.
3. In response to the growing prevalence of the aarch64 architecture, which is the 64-bit version of the ARM architecture utilized in various devices such as smartphones, tablets, and servers, we have incorporated assembly mode implementation into ckb-vm specifically for aarch64. By running ckb-vm on assembly mode, users can potentially experience improved performance with faster execution times, ultimately enhancing the overall efficiency of the system.
4. Refactor ckb-vm to make it thread-safe. Thread-safe ckb-vm can take advantage of modern multi-core CPUs and execute multiple threads in parallel, potentially improving performance and throughput. At the same time, many modern applications and frameworks rely on multi-threading, and a thread-unsafe virtual machine may not be compatible with these technologies.
5. [Macro-Operation Fusion](https://en.wikichip.org/wiki/macro-operation_fusion). There are 5 MOPs added in VM version 2, there are:
1. One notable addition is the inclusion of a new system call called "Spawn," In essence, Spawn serves as an alternative to dynamic library calls and Exec.
2. In response to the growing prevalence of the aarch64 architecture, which is the 64-bit version of the ARM architecture utilized in various devices such as smartphones, tablets, and servers, we have incorporated assembly mode implementation into ckb-vm specifically for aarch64. By running ckb-vm on assembly mode, users can potentially experience improved performance with faster execution times, ultimately enhancing the overall efficiency of the system.
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I don't think assembly implementation of CKB-VM for aarch64 is tied to version 2.

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We will submit another PR for these 2 issues.

3. Refactor ckb-vm to make it thread-safe. Thread-safe ckb-vm can take advantage of modern multi-core CPUs and execute multiple threads in parallel, potentially improving performance and throughput. At the same time, many modern applications and frameworks rely on multi-threading, and a thread-unsafe virtual machine may not be compatible with these technologies.
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Personally I wasn't sure what this refers to

4. [Macro-Operation Fusion](https://en.wikichip.org/wiki/macro-operation_fusion). There are 5 MOPs added in VM version 2, there are:

| Opcode | Origin | Cycles | Description |
| --- | --- | --- | --- |
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