From: "kjtsanaktsidis (KJ Tsanaktsidis) via ruby-core" <ruby-core@...>
Date: 2023-11-15T09:26:55+00:00
Subject: [ruby-core:115396] [Ruby master Feature#20005] Add C API to return symbols of native extensions resolved from features

Issue #20005 has been updated by kjtsanaktsidis (KJ Tsanaktsidis).





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:



> If filename is NULL, then the returned handle is for the main

> program.  When given to dlsym(3), this handle causes a search for

> a symbol in the main program, followed by all shared objects

> loaded at program startup, and then all shared objects loaded by

> dlopen() with the flag RTLD_GLOBAL.



Ruby uses RTLD_GLOBAL to load extensions I think, so any symbols exported by extensions should be accessible 





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

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

https://bugs.ruby-lang.org/issues/20005#change-105333



* 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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