Re: [PATCH, expand] Call misaligned memory reference in expand_builtin_return [PR112417]

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Nov 10, 2023 at 8:52 AM HAO CHEN GUI <guihaoc@linux.ibm.com> wrote:
>
> Hi Richard,
>   Thanks so much for your comments.
>
> 在 2023/11/9 19:41, Richard Biener 写道:
> > I'm not sure if the testcase is valid though?
> >
> > @defbuiltin{{void} __builtin_return (void *@var{result})}
> > This built-in function returns the value described by @var{result} from
> > the containing function.  You should specify, for @var{result}, a value
> > returned by @code{__builtin_apply}.
> > @enddefbuiltin
> >
> > I don't see __builtin_apply being used here?
>
> The prototype of the test case is from "__objc_block_forward" in
> libobjc/sendmsg.c.
>
>   void *args, *res;
>
>   args = __builtin_apply_args ();
>   res = __objc_forward (rcv, op, args);
>   if (res)
>     __builtin_return (res);
>   else
>     ...
>
> The __builtin_apply_args puts the return values on stack by the alignment.
> But the forward function can do anything and return a void* pointer.
> IMHO the alignment might be broken. So I just simplified it to use a
> void* pointer as the input argument of  "__builtin_return" and skip
> "__builtin_apply_args".

But doesn't __objc_forward then break the contract between
__builtin_apply_args and __builtin_return?

That said, __builtin_return is a very special function, it's not supposed
to deal with what you are fixing.  At least I think so.

IMHO the bug is in __objc_block_forward.

Richard.

>
> Thanks
> Gui Haochen