Versioned Symbols in Shared Libraries

[Sebastian Stenzel]

Thanks for the suggestion, a quick test [1] shows that a custom SymbolLookup based on dlvsym does in fact work (hooray!)

However, this isn't (yet?) very practical with jextract, because:
1. afaik there is no way to tell it to use a custom SymbolLookup
2. jextract'ed code defines method handles eagerly (static constants) - while the lib may not yet be opened during class loading
2. we have to add versions to symbol names for all jextracted code manually

All this can be solved manually, but re-jextract-ing isn't much fun, eliminating one of its benefits, which (at least to me) is rapidly adjusting Java code to upstream native library changes.

[1] https://github.com/cryptomator/jfuse/commit/85b296c1d361d3756b6fa842b2827fe63700e535

> On 29. Sep 2022, at 16:58, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
> 
> Hi Sebastian,
> Sadly, `dlopen` only does unversioned lookups (unless you use some tricks, like the RTLD_NEXT pseudo handles, which we don't use). On *nix systems another primitive for looking up symbols exists, namely `dlvsym` which takes an extra string pointer (the version).
> 
> So, I think your best bet would to create your own SymbolLookup which can be initialized with a given version number, which is then passed to calls to `dlvsym`.
> 
> Since this capability doesn't make sense on platforms other than GCC (I believe), adding support for versioning in SymbolLookup itself would seem a bit odd.
> 
> Maurizio
> 
> On 29/09/2022 12:49, Sebastian Stenzel wrote:
>> Hi,
>> 
>> Today I learned about versioned symbols when investigating a downwards compatibility problem in a jextract'ed API. See discussion [1]
>> 
>> The concept is new to me, but apparently broadly used to make sure to invoke the exact function that was referenced at compile time. Since jextract only knows the header files, I suppose it isn't aware of such versions? Does the SymbolLookup API provide any mechanism to lookup a specific version?
>> 
>> I hope you can make sense of what I'm asking as this is all new to me and I'm not sure I'm asking the right questions.
>> 
>> Thank you!
>> 
>> [1]: https://github.com/libfuse/libfuse/discussions/701