[PATCH] D16738: Fix invalid casts in <functional>.

Eric Fiselier via cfe-commits cfe-commits at lists.llvm.org
Sat Jan 30 19:57:53 PST 2016

EricWF added a comment.

> This also could be fixed in a different way by replacing C-style

>  casts with reinterpret_cast<>, which, from my reading of the

>  standard, is allowed in this context.

I agree that using `void*` to represent raw memory is the better approach than `reinterpret_cast<>()`.
However I'm concerned that changing the signature (and mangling) of `virtual void __clone(...)` could cause ABI problems.
I *think* this should be "safe" because the VTable's mangled name doesn't change. but if I'm wrong we must use `reinterpret_cast<>` for calls to `__clone(...)`.

The parts of the patch that don't affect `__clone(...)` LGTM. You can commit them separably if you want.

> That would not help with CFI

>  though, which still flags such casts as invalid (yes, it is stricter that the standard).

I'm sure there are alternative ways to make CFI shut up. Perhaps we could do the `Buffer* -> Base*` conversion inside a blacklisted function (akin to std::launder)?
It would also be nice to have "`__attribute__((__no_sanitize__("cfi")))`.

Comment at: include/functional:1443
@@ -1442,3 +1442,3 @@
     virtual __base* __clone() const = 0;
-    virtual void __clone(__base*) const = 0;
+    virtual void __clone(void*) const = 0;
     virtual void destroy() _NOEXCEPT = 0;
Doesn't this break the ABI because it changes the mangling of a virtual function? I understand the vtable should remain layout compatible but I suspect the mangling change is an issue.

Comment at: include/functional:1739
@@ -1738,2 +1738,3 @@
+            ::new (&__buf_) _FF(_VSTD::move(__f));
             __f_ = (__base*)&__buf_;
`__f_ = ::new((void*)&__buf_) _FF(_VSTD::move(__f));`



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