------- Comment #5 from dave dot korn dot cygwin at gmail dot com 2009-05-10 11:17 ------- (In reply to comment #4) > Hello Dave,
Hi Danny! > Rather than use DLL linkage (and so force client to resort to auto-import > magic) > why not just always emit the RTTI with one-only comdat linkage. I have your patch in the cygwin distro compiler where it works fine, but I am concerned about what unforeseeable problems could arise by violating ODR in this way. I don't have any concrete evidence of any problem yet, it is just a worry. Also, I don't think this is necessarily an either-or situation; we could add my patch and have the typeinfo exported from the DLL, and also add yours so that clients could link a comdat copy (which would override the import stub) until we have a better solution for importing from the DLL. Or I could follow up with another patch that propagates dllimport attributes from class to typeinfo. There is of course this: /* We leave typeinfo tables alone. We can't mark TI objects as dllimport, since the address of a secondary VTT may be needed for static initialization of a primary VTT. VTT's of dllimport'd classes should always be link-once COMDAT. */ /* Do not import tinfo nodes if the class has dllimport attribute. Dllimports do not have a constant address at compile time, so static initialization of tables with RTTI fields is a problem. Set to comdat instead. */ ... but I do not see why this should be a problem in these days of auto-import and pseudo-relocs; do you know more about what the actual problem is (or was) here? Is this not basically the same situation as something like ----dll_A.c---- int foo; int __attribute__ ((dllexport)) * bar = &foo; ----dll_B.c---- extern int __attribute__ ((dllexport)) * bar; int __attribute__ ((dllexport)) * baz = &bar; --------------- the example above? If it's possible to solve either in the compiler or further down the toolchain, I would very much like to do so. Also, how come emitting the typeinfo .linkonce as we currently do isn't the same as COMDAT for these purposes? cheers, DaveK -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40068