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by speed_spread 167 days ago
It's not just about memory. I'd like to have a stable Rust ABI to make safe plugin systems. Large binaries could also be broken down into dynamic libraries and make rebuilds much faster at the cost of leaving some optimizations on the table. This could be done today with a semi stable versionned ABI. New app builds would be able to load older libraries.

The main problem with dynamic libraries is when they're shared at the system level. That we can do away with. But they're still very useful at the app level.
1 comments
SkiFire13 167 days ago
> I'd like to have a stable Rust ABI to make safe plugin systems

A stable ABI would allow making more robust Rust-Rust plugin systems, but I wouldn't consider that "safe"; dynamic linking is just fundamentally unsafe.

> Large binaries could also be broken down into dynamic libraries and make rebuilds much faster at the cost of leaving some optimizations on the table.

This can already be done within a single project by using the dylib crate type.

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speed_spread 167 days ago
Loading dynamic libraries can fail for many reasons but once loaded and validated it should be no more unsafe than regular crates?
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VorpalWay 167 days ago
You could check that mangled symbols match, and have static tables with hashes of structs/enums to make sure layouts match. That should cover low level ABI (though you would still have to trust the compiler that generated the mangling and tables).

A significantly more thorny issue is to make sure any types with generics match, e.g. if I declare a struct with some generic and some concrete functions, and this struct also has private fields/methods, those private details (that are currently irrelevant for semver) would affect the ABI stability. And the tables mentioned in the previous paragraph might not be enough to ensure compatibility: a behaviour change could break how the data is interpreted.

So at minimum this would redefine what is a semver compatible change to be much more restricted, and it would be harder to have automated checks (like cargo-semverchecks performs). As a rust developer I would not want this.

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remexre 167 days ago
What properties are you validating? ld.so/libdl don't give you a ton more than "these symbols were present/absent."
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