> There's no "for a long time" here. The ABI does not allow us to emit these > symbols with non-coalescing linkage. We're not going to break ABI > just because people didn't consider a particular code pattern when they > hacked in devirtualization through external v-tables.
If we take "the ABI" to mean compatibility with released versions of the compilers, then it *is* broken, as released compilers assume behavior that is not guaranteed by the ABI (the document). It is not possible to avoid all incompatibilities. To avoid most we would have to * Say that the symbol must be exported by the file that exports the vtable. Not doing so causes incompatibilities with files compiled by gcc version 4.6 and 4.7, open source clang versions 2.9, 3.0, 3.1 and Apple's releases 318.0.58 and 421-10.48 (those are the ones I have on my laptop). * Say that the symbol must remain mergeable so that current files still work, which on OS X requires it to be weak. In other words, we have to take the worse of both options. The only thing that would still be broken (in released versions) are libraries built with gcc's LTO, but hopefully changing that is the option with the least impact on the users. > John. Cheers, Rafael
