Re: Using "weak externals" with ld on cygwin?

[Brooks Moses <bmoses@stanford.edu>]

Danny Smith wrote:
> Brooks Moses <bmoses at stanford dot edu> 
> wrote on: Tue, 11 Apr 2006 23:34:14 -0700 
>>My understanding of this is that I should be able to create a libA.dll
>>file with some code in it that references a function foo(), and define
>>foo() as a weak symbol aliased to bar() such that, if an executable
>>defines its own foo() or links to another dll that defines it, the libA
>>code will use that definition of foo(), but otherwise it will use bar().
>>Is that actually a correct understanding? Or am I missing something
>>somewhere?
> 
> weak symbols do not work as expected with PE DLL's.  DLL's do not allow
> undefined symbols when they are linked together.  DLLs are executables
> with their own startup entry point, their own main, their own at_exit
> table, etc. Hence a DLL built from this:
[...]
> Weak extern synbols work fine in PE  with static objects and archives,
> but I don't
> know how to do exactly what you want with dll's.  Using
> LoadLibrary/GetProcAddress API might work for you.

Thanks!  Sounds like the best answer to my "How do I do this with dlls?" 
question is "Don't; find a workaround instead" -- making my code work 
with the LoadLibrary API would probably be as much work as simply fixing 
it so I don't need the circularly-referencing dlls, and the latter is a 
much more elegant solution.

>>I've been trying, with a copy of the release version of gcc 4.1.0 and
>>the latest Cygwin version of ld (which reports GNU ld version 2.16.91
>>20050610 as its version), to write some code that will do that.
>>Everything I try seems to either give me an error like "Cannot export
>>.weak.__Z3foov.__Z3barv: symbol not found" or else always uses bar()
>>regardless of whether I supply a foo() elsewhere. 
> 
> Exporting .weak._foo._bar in the above is an ld error.  I think this
> kind of
> '.'-concatted names get interpreted as a forward export, eg the loader
> will look
> for a symbol 'weak' in another dll module with the unsual name
> '_foo._bar'. 
> This can be fixed easily enough by adding ".weak." to the list of
> prefixes that
> exclude symbols from automatic export, like so:
[...]

Should I file a bug report on this, then?  If so, where?

Thanks much!
- Brooks