[cxx-abi-dev] Passing non-trivial types through ...

[John McCall]

On Aug 13, 2014, at 2:51 PM, Jason Merrill <jason at redhat.com> wrote:
> On 08/13/2014 05:38 PM, Dennis Handly wrote:
>> Did the customer say how he was going to accept it on the callee side?
> 
> My proposal is that this would all be handled transparently by the compiler, which knows which types need to be handled this way.
> 
>> aCC6 allows it with a warning but the results are unpredictable:
>> warning #3290-D:  Passing a non-POD object to a function with variable
>> arguments has undefined behavior.  Object will be copied onto
>> the stack instead of using a constructor.
>> 
>> (This is a bitwise copy.)
> 
> Ah, so my proposal would be incompatible with the current aCC behavior.  Hmm.

I agree that this is a problem; we shouldn't “standardize" something that a vendor doesn’t feel they can reasonably adopt.

We could document it as a recommendation, I suppose.

Out of curiosity, how does aCC handle destruction of the argument?  Does it call the destructor at the argument's original location or its new location in the arguments area?

John.