From: "nobu (Nobuyoshi Nakada) via ruby-core" <ruby-core@...>
Date: 2023-11-15T13:47:28+00:00
Subject: [ruby-core:115397] [Ruby master Feature#20005] Add C API to return symbols of native extensions resolved from features

Issue #20005 has been updated by nobu (Nobuyoshi Nakada).





kjtsanaktsidis (KJ Tsanaktsidis) wrote in #note-5:

> True, dlopen/dlsym have some portability issues, but:

> 

> > dlsym needs the handle of the loaded library, and it is not trivial to retrieve the path from the feature name.

> 

> Can���t you just call `dlopen(NULL)` to get this? From the Linux man page:



It returns `RTLD_DEFAULT`, no `dlopen` call is needed.

This special handle searches all loaded libraries in the loaded order.

That means it can't find a shadowed symbol.

Additionally, macOS man page says "This can be a costly search and should be avoided."



And another portability concern is exported symbols may be prefixed with "_".



Anyway it doesn't look a nice idea to make extensions libraries write `#ifdef _WIN32` unnecessarily here and there.



I consider the wrapper API would be reasonable for these reasons.



----------------------------------------

Feature #20005: Add C API to return symbols of native extensions resolved from features

https://bugs.ruby-lang.org/issues/20005#change-105334



* Author: tagomoris (Satoshi Tagomori)

* Status: Open

* Priority: Normal

----------------------------------------

I want an API to resolve symbols of other native extensions by a feature name and a symbol name (just like `dlsym`).



(`rb_dln_resolve_symbol` is an example function name of this feature in the example below)

```c

// "a_client_open" is a function defined in "/..../a_client.so", that should be loaded in Ruby beforehand.



// in the extension to be "a.so"

VALUE (*a_client_open)(VALUE);



void Init_a(void)

{

  a_client_open = (VALUE(*)(VALUE))rb_dln_resolve_symbol("a_client", "a_client_open");

  // the return value may be NULL if the symbols is not found

}

```



This API is to replace direct reference of external symbols.



Currently, native extensions have to just call the function of other extensions directly on the assumption of:

* The dependency native extension is already loaded

* The symbol is defined correctly in the dependency (the version of dependency is correct&expected)

Otherwise, it crashes.



This API provides a way for developers to raise exceptions if the resolved symbol is `NULL`, and these exceptions can display meaningful messages and instructions to the users of extensions.









-- 

https://bugs.ruby-lang.org/

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