Am Sun, 11 Nov 2012 18:49:18 -0800 schrieb Ellery Newcomer <ellery-newco...@utulsa.edu>:
> Playing with pypy. > > I build me a shared library with ldc and try to access it via ctypes, > and it gives me a > > /usr/lib64/libdruntime-ldc.so.60: undefined symbol: __data_start How did you link that shared lib? With ld, gcc or g++? If you link via gcc it pulls in some special object files, one of these could contain __data_start. g++ pulls in some more object files for c++ support, but that's probably not necessary here. > > So the natural question is what is __data_start? Am I right in > assuming it is a symbol that points to the data section or something > and that it is relevant in executables but not shared libraries (and > thus shouldn't be in druntime for shared lib builds)? There doesn't seem to be much documentation about __data_start. It's a C library / linker symbol, but I think it's local to each shared object. So only the main application can access _it's_ __data_start, and according to some sources each shared library should get it's own __data_start. I don't know why it's not defined in your case. It does mark the start of the data section of the module accessing it but each module (app/shared object) has it's own data section and therefore needs a different __data_start. See also: http://forum.dlang.org/thread/ftnv6c$2odr$1...@digitalmars.com#post-ftpobo:24oi:241:40digitalmars.com But anyway, the runtime uses __data_start to find the data section which should be scanned by the gc (see rt.memory). I really doubt this approach will work in an application with multiple shared libraries.
