On Sep 25, 2013, at 9:42 AM, G M <[email protected]> wrote: > Hi Everyone > > The attached patch is for libcxx's new.cpp and __config files. The patch's > intent is to make new.cpp compile using MS's cl.exe compiler without changing > the meaning of anything for any other compiler. > > The issue this patch seeks to address is that MS's compiler (cl.exe) doesn't > support the __attribute__((__weak__)) or > __atribute__((__visibility__("default")) syntax; so a solution must be found > where cl.exe doesn't see this syntax. > > This patch seeks to solve this problem by changing code patterned like this: > __attribute__((__weak__, __visibility__("default"))) > void* operator new(size_t size, const std::nothrow_t&) _NOEXCEPT { /*snip*/; > return p; } > > to code like this: > _LIBCPP_WEAK > void* operator new(size_t size, const std::nothrow_t&) _NOEXCEPT { return p; } > > with the expectation that this change will NOT introduce any functionality > change for clang++/g++ etc. That expectation is based on two aspects of the > change: > > * The first is the belief that cl.exe doesn't support "weak" in any > documented way and that libcxx on Windows doesn't need it anyway. So > _LIBCPP_WEAK is defined as nothing when cl.exe is the detected compiler. > > For all other compilers, _LIBCPP_WEAK is defined to be just > __attribute__((__weak__)) and nothing more). > This should mean that cl.exe doesn't see the weak attribute syntax and so > won't choke on it; and g++/clang++ will see the same weak attribute that it > saw before this patch. > > * The second part is what to do about > __attribute__((_visibility__("default"))) as in the proposed change it is > dropped from the function definition. > > The expecatation here is that this is ok because it isn't neccessary because > the prototype for the modified functions already have it; so the right thing > should still happen. > If all of this is correct, then this patch should fix new.cpp for cl.exe > without changing anything else. > > It also provides a pattern that will work with all the compilers libcxx > already supports; and without having to introduce alternate #if/#else guards > or other uglyness. This should make it better match the patterns libcxx > already uses. > If removing the "default" attribute turns out to be a problem, I believe the > default attribute could be added back now that it is decoupled from the > "weak" attribute (which I think is a good thing in of itself) by using one of > libcxx's existing macro's such as _LIBCPP_FUNC_VIS / _LIBCPP_NEW_DELETE_VIS > etc. > > I'm not sure of the neccessity of LIBCPP_NEW_DELETE_VIS or it's realtionship > to _LIBCPP_FUNC_VIS at this point, FWIW, but that doesn't matter to the logic > of this patch. > > I compiled this patch with cl.exe, g++ and clang++.exe. > > Please let me know what you think. If this patch doesn't get traction, I'd > appreciate some advice with real alternative code that could be used to > advance things here as I found it hard to produce something actionable from > the comments I received to my previous patch for this problem though I did > and do appreciate the responses. > > Thanks > <libcxx_weak.diff>
Committed revision 192007. See commit comments for minor modifications to the patch. Thanks, Howard _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
