rmaprath added a comment. In http://reviews.llvm.org/D20677#442713, @EricWF wrote:
> In http://reviews.llvm.org/D20677#442687, @rmaprath wrote: > > > In http://reviews.llvm.org/D20677#442559, @EricWF wrote: > > > > > I have an issue with this change since it allows a libc++abi built > > > without exceptions to be used in a program compiled with them. I assert > > > that this should not be supported in any way. > > > > > > My personal preference would be to remove as much of the exception API > > > from the library when it's built without exceptions. This should cause > > > link errors if a program contains any code that throws. If this is not > > > done it creates bugs within code like `__terminate` as mentioned in an > > > inline comment. > > > > > > I would like to see another revision of this patch that removes as much > > > of the exception API as possible. Looking at the symbols defined in > > > `cxxabi.h` I would say ever symbol in sections 2.4 and 2.5 should not > > > longer be defined in the library. > > > > > > That sounds generally OK to me. The toolchain I'm working on (ARM Compiler > > 6) has an elaborate mechanism (based on build attributes) to select the > > correct variant of libraries. In other words, if any of your objects are > > compiled with exceptions, you are guaranteed to no select any of the > > no-exceptions library variants. This avoids the problem you mentioned > > altogether. > > > Note that that behavior will cause different issues in some cases. If you > link an executable to two libraries, `libfoo.so` and `libbar.so`, where one > was compiled with exceptions and the other without you'll get two copies of > libc++abi in the program. Now you have two copies of the global terminate > handler and two copies of `__terminate` for the linker to select from. > If it selects the nothrow `__terminate` and the terminate handler throws an > exception your in trouble. In this case, I expect the linker to only select one variant of libc++abi (the one with exceptions). The idea behind build-attributes is to capture user intentions, if the user links his program with `libbar.a` and `libfoo.a` user libraries (with and without exceptions), the linker would assume that the user meant to use exceptions rather than not, and hence select the with-exceptions libc++abi variant. The theory behind build-attributes is bit more complicated that that though, I'm not the best person to go on about this. In any case, I agree that getting the linker to produce an error (when linking with-exceptions objects with a no-exceptions libc++abi) is much more clearer. I have a small concern about how difficult this would make things for us though - our toolchain setup uses `-ffunction-sections` and `-fdata-sections` along with linker's unused-section elimination to get rid of most of the stuff not necessary for the final image, but I can't remember if unused-section elimination happens before or after checking for missing symbols. If it is the latter, then we might be in trouble with this approach. I will have a look into this when I get back to work. Cheers, / Asiri http://reviews.llvm.org/D20677 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
