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

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

On Mon, Nov 13, 2023 at 9:09 AM HAO CHEN GUI <guihaoc@linux.ibm.com> wrote:
>
> Sorry, forgot to cc gcc-patches.
>
> 在 2023/11/13 16:05, HAO CHEN GUI 写道:
> > Andrew,
> >   Could you kindly inform us what's the functionality of __objc_forward?
> > Does it change the memory content pointed by args? Thanks a lot.
> >
> > Thanks
> > Gui Haochen
> >
> >
> > libobjc/sendmsg.c.
> >
> >    void *args, *res;
> >
> >    args = __builtin_apply_args ();
> >    res = __objc_forward (rcv, op, args);

maybe this should use __builtin_apply and the
__builtin_return use 'args', not 'res' as the return value?

> >    if (res)
> >      __builtin_return (res);
> >    else
> >      ...
> >
> > -------- 转发的消息 --------
> > 主题: Re: [PATCH, expand] Call misaligned memory reference in expand_builtin_return [PR112417]
> > 日期: Fri, 10 Nov 2023 14:39:02 +0100
> > From: Richard Biener <richard.guenther@gmail.com>
> > 收件人: HAO CHEN GUI <guihaoc@linux.ibm.com>
> > 抄送: gcc-patches <gcc-patches@gcc.gnu.org>, Kewen.Lin <linkw@linux.ibm.com>
> >
> > On Fri, Nov 10, 2023 at 11:10 AM HAO CHEN GUI <guihaoc@linux.ibm.com> wrote:
> >>
> >> Hi Richard,
> >>
> >> 在 2023/11/10 17:06, Richard Biener 写道:
> >>> 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.
> >>
> >> If so, can we document that the memory objects pointed by input argument of
> >> __builtin_return have to be aligned? Then we can force the alignment in
> >> __builtin_return. The customer function can do anything if gcc doesn't state
> >> that.
> >
> > I don't think they have to be aligned - they have to adhere to the ABI
> > which __builtin_apply_args ensures.  But others might know more details
> > here.
> >
> >> Thanks
> >> Gui Haochen
> >>
> >>>
> >>> Richard.
> >>>
> >>>>
> >>>> Thanks
> >>>> Gui Haochen