[cxx-abi-dev] Type mismatch in __cxa_atexit and __cxa_finalize

[Mark Mitchell]

Matt Austern wrote:

> Maybe this is old news; I'm sure everyone who has implemented atexit in 
> terms of __cxa_atexit must have noticed it already.

I believe that GNU libc implemented both atexit and __cxa_atexit atop 
some other interface, but I haven't looked in a long time.

> The obvious fix would be to say that:
>  1. atexit(f) invokes __cxa_atexit((void(*)(void*)) f, 0, 0).
>  2. If you're passing __cxa_atexit a function that does take an 
> argument, the parameter may not be 0.
>  3. When __cxa_finalize invokes a function f on a parameter p, it should 
> do the equivalent of:
>      if (p)
>         (*f)(p);
>      else
>        (*((void (*)(void)) f))();

That's a reasonable approach, but point (2) worries me -- that might 
represent a change for some existing implementations.

An alternative would be to remove the explicit impliciation in the ABI 
that atexit is implemented atop __cxa_atexit, and just indicate that (a) 
the calls to the registered functions must be interleaved in the 
appropriate way, and (b) __cxa_finalize called with a NULL DSO parameter 
must call the functions registered with atexit.

Thoughts?

-- 
Mark Mitchell
CodeSourcery, LLC
mark at codesourcery.com