Re: C++ RTTI/dynamic_cast across shared module boundaries?
Re: C++ RTTI/dynamic_cast across shared module boundaries?
- Subject: Re: C++ RTTI/dynamic_cast across shared module boundaries?
- From: Michael Rice <email@hidden>
- Date: Fri, 17 Feb 2006 18:55:58 -0600
It sounds like you are running into the C++ ABI described in the GCC
FAQ (http://gcc.gnu.org/faq.html#dso). I ran into this problem long
ago and have still to find a good, generic solution for this problem
(i.e., not having to export every symbol in the library). My best
solution so far has been to implement my own, less efficient, RTTI
system.
On Feb 17, 2006, at 8:43 AM, Zachary Pincus wrote:
Thanks Howard.
In the Code Generation build settings of all targets, uncheck
"Symbols Hidden by Default".
Right now, I'm not actually using XCode (part of my debugging was
to remove XCode from the mix and do all of the building and linking
directly on the command line, so I could easily fix problem flags).
There are absolutely no '-fvisibility=hidden' flags on the link or
compile command lines I have been using, so I don't think symbols
are being hidden. (Given that the man page for g++ says that the
default is for public visibility.)
Is there any way I verify this with, say, otool?
Also, a correction: telling Python to load with *either* dyld flags
of RTLD_LAZY|RTLD_GLOBAL *or* RTLD_NOW|RTLD_GLOBAL doesn't help.
Zach
On Feb 17, 2006, at 8:24 AM, Howard Hinnant wrote:
On Feb 17, 2006, at 9:01 AM, Zachary Pincus wrote:
Hi folks,
I've been trying for a while to get c++ RTTI and dynamic casting
to work across the boundaries of several "bundle" shared modules.
I've spent a day looking at man pages and online, to no avail.
In my case, instances of particular classes can be created in
various modules, but need to work (and dynamically cast properly)
when passed to other modules. (Before you ask: it's an image
processing library, where different image filter types are
defined in different modules, but they all need to be able to
send and receive the same image types.)
I've linked the modules as follows:
/usr/bin/c++ -bundle -o [output].so [object files] -L[link paths]
-l[link libs]
Now, how do I need to set up my environment to get RTTI and
dynamic_cast working across several such modules?
Right now, the module loader is Python, which I think uses dlopen
to load the modules. I've set the dlopen flags (in python,
sys.setdlopenflags()) to 0x9, which is RTLD_LAZY|RTLD_GLOBAL (as
they are defined in /usr/include/dlfcn.h), but that really
doesn't help. (Other permutations on the dlopen flags don't help.)
Is there anything else I need to do? Is there anything else I can
try? Is this a hopeless project?
In the Code Generation build settings of all targets, uncheck
"Symbols Hidden by Default".
-Howard
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