bytecodealliance/wasmtime

Eagerly cast pointers in aarch64 relocation code to `usize` to avoid `unsafe` blocks in cranelift-jit

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#7,588 创建于 2023年11月27日

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 (2 评论) (0 反应) (0 负责人)Rust (17,002 star) (1,531 fork)batch import
good first issue

描述

When performing relocations in cranelift-jit, there are many introductions of a variable what that's defined as an unsafe pointer offset. These variables are almost always cast to usize or isize before they're used, so perhaps we should instead turn the base pointer into its target numeric type eagerly, to avoid needing the unsafe blocks for calling the offset method on the pointers.

https://github.com/bytecodealliance/wasmtime/blob/cd97c9f14713d81de5453fb9861319e78a761432/cranelift/jit/src/compiled_blob.rs#L55-L57

贡献者指南

技术栈
rustwasm
领域
backenddeveloper experience
议题类型
refactor
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
1-3 hours
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
stale
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
Rustunsafe Rustpointer arithmetic
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
40
研究方向
Examine the file `cranelift/jit/src/compiled blob.rs`, specifically lines 55-57 and surrounding code, to understand how the `what` pointer is used in relocation functions. Identify all occurrences where pointers are cast to `usize` or `isize` after offset calculations. Implement a change that casts the base pointer to `usize` early to avoid `unsafe` blocks for pointer offset calls.