[Pythonmac-SIG] -Wl, -x in distutils module linking causes crashes

[Jack Jansen]

On 22-sep-03, at 23:15, Bob Ippolito wrote:
> You're right, that wasn't very clear.  I meant "it's possible to get 
> around the -Wl,-x problem by explicitly stating which symbols you 
> need", but now that I think about it they're going to be nasty mangled 
> C++ crap.  However, I did find a workaround, -Wl,-Sn (discard no 
> symbols) in extra_link_args will override the -Wl,-x directive.

Now your original statement is clear, but I'm confused about how this 
works. Why are non-global symbols important to C++ static 
initialization? I hope you're not going to tell me that the runtime 
system somehow looks at the symbol table during dynamic loading and 
calls all routines whose names fit a certain pattern...

And the "-Wl,-Sn" bit is too much of a hack for my liking. If there is 
the possibility of extensions that need non-global symbols to be intact 
we should just get rid of -Wl,-x.

>> And if the bind_at_load is needed for C++: is it a good idea to add 
>> it to the standard Python Makefile, so distutils will pick it up 
>> automatically, or are there adverse consequences to it?
>
> It's only needed for C++ that uses static initializers.  Not everybody 
> uses these.  Can't we detect if C++ is being used and toggle the link 
> flags on a per-extension basis when on darwin (append ["-Wl,-Sn", 
> "-Wl,-bind_at_load"] to extra_link_flags)?  I believe distutils can 
> detect the language, because Extension accepts an optional language 
> parameter.

Too dangerous. The extension itself could be C, but depend on a C++ 
library or something.
And counting on C++ users not using a first-class language feature is 
also a road I don't
want to go down...

>   Also, a typical C++ program will probably link to stdc++, which 
> could be an alternative trigger for linking special behavior.

Hmm, this is interesting. I've noticed that adding "-lstdc++" solved 
some problems. But from your example not all problems, as in your Mk4py 
you also added the bind_at_load magic....

Hmm again: is all this strangeness Apple-specific, or is it a general 
GCC C++ problem? I.e. on other platforms, can people get away with 
linking extensions that may have some C++ code in them normally, or is 
there always magic involved?
--
Jack Jansen, <Jack.Jansen at cwi.nl>, http://www.cwi.nl/~jack
If I can't dance I don't want to be part of your revolution -- Emma 
Goldman