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From: Qing Zhao <qing.zhao@oracle.com>
To: Richard Biener <richard.guenther@gmail.com>,
	Martin Sebor <msebor@gmail.com>
Cc: Jakub Jelinek <jakub@redhat.com>,
	gcc-patches Paul A Clarke via <gcc-patches@gcc.gnu.org>,
	kees Cook <keescook@chromium.org>
Subject: Re: [GCC 13][PATCH] PR101836: Add a new option -fstrict-flex-array[=n] and use it in __builtin_object_size
Date: Wed, 6 Jul 2022 14:20:15 +0000	[thread overview]
Message-ID: <F9B7B015-4CF1-4656-AEB1-69BF8DAD5182@oracle.com> (raw)
In-Reply-To: <CAFiYyc2S9UvrED1xsMq0StuUwKVy0nUnqk=v4cNR14X7=d4gRg@mail.gmail.com>

(Sorry for the late reply, just came back from a short vacation.)

> On Jul 4, 2022, at 2:49 AM, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Fri, Jul 1, 2022 at 5:32 PM Martin Sebor <msebor@gmail.com> wrote:
>> 
>> On 7/1/22 08:01, Qing Zhao wrote:
>>> 
>>> 
>>>> On Jul 1, 2022, at 8:59 AM, Jakub Jelinek <jakub@redhat.com> wrote:
>>>> 
>>>> On Fri, Jul 01, 2022 at 12:55:08PM +0000, Qing Zhao wrote:
>>>>> If so, comparing to the current implemenation to have all the checking in middle-end, what’s the
>>>>> major benefit of moving part of the checking into FE, and leaving the other part in middle-end?
>>>> 
>>>> The point is recording early what FIELD_DECLs could be vs. can't possibly be
>>>> treated like flexible array members and just use that flag in the decisions
>>>> in the current routines in addition to what it is doing.
>>> 
>>> Okay.
>>> 
>>> Based on the discussion so far, I will do the following:
>>> 
>>> 1. Add a new flag “DECL_NOT_FLEXARRAY” to FIELD_DECL;
>>> 2. In C/C++ FE, set the new flag “DECL_NOT_FLEXARRAY” for a FIELD_DECL based on [0], [1],
>>>     [] and the option -fstrict-flex-array, and whether it’s the last field of the DECL_CONTEXT.
>>> 3. In Middle end,  Add a new utility routine is_flexible_array_member_p, which bases on
>>>     DECL_NOT_FLEXARRAY + array_at_struct_end_p to decide whether the array
>>>     reference is a real flexible array member reference.
> 
> I would just update all existing users, not introduce another wrapper
> that takes DECL_NOT_FLEXARRAY
> into account additionally.

Okay. 
> 
>>> 
>>> 
>>> Middle end currently is quite mess, array_at_struct_end_p, component_ref_size, and all the phases that
>>> use these routines need to be updated, + new testing cases for each of the phases.
>>> 
>>> 
>>> So, I still plan to separate the patch set into 2 parts:
>>> 
>>>   Part A:    the above 1 + 2 + 3,  and use these new utilities in tree-object-size.cc to resolve PR101836 first.
>>>                  Then kernel can use __FORTIFY_SOURCE correctly;
>>> 
>>>   Part B:    update all other phases with the new utilities + new testing cases + resolving regressions.
>>> 
>>> Let me know if you have any comment and suggestion.
>> 
>> It might be worth considering whether it should be possible to control
>> the "flexible array" property separately for each trailing array member
>> via either a #pragma or an attribute in headers that can't change
>> the struct layout but that need to be usable in programs compiled with
>> stricter -fstrict-flex-array=N settings.
> 
> Or an decl attribute.

Yes, it might be necessary to add a corresponding decl attribute 

strict_flex_array (N)

Which is attached to a trailing structure array member to provide the user a finer control when -fstrict-flex-array=N is specified. 

So, I will do the following:


*****User interface:

1. command line option:
     -fstrict-flex-array=N       (N=0, 1, 2, 3)
2.  decl attribute:
     strict_flex_array (N)      (N=0, 1, 2, 3)


*****Implementation:

1. Add a new flag “DECL_NOT_FLEXARRAY” to FIELD_DECL;
2. In C/C++ FE, set the new flag “DECL_NOT_FLEXARRAY” for a FIELD_DECL based on [0], [1],
     [], the option -fstrict-flex-array, the attribute strict_flex_array,  and whether it’s the last field 
     of the DECL_CONTEXT.
3. In Middle end,   update all users of “array_at_struct_end_p" or “component_ref_size”, or any place that treats
    Trailing array as flexible array member with the new flag  DECL_NOT_FLEXARRAY. 
    (Still think we need a new consistent utility routine here). 


I still plan to separate the patch set into 2 parts:

Part A:    the above 1 + 2 + 3,  and use these new utilities in tree-object-size.cc to resolve PR101836 first.
	       Then kernel can use __FORTIFY_SOURCE correctly.
Part B:    update all other phases with the new utilities + new testing cases + resolving regressions.


Let me know any more comment or suggestion.

Thanks a lot.

Qing



  reply	other threads:[~2022-07-06 14:20 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-27 14:19 Qing Zhao
2022-06-28  7:16 ` Richard Biener
2022-06-28 15:03   ` Qing Zhao
2022-06-28 15:08     ` Jakub Jelinek
2022-06-28 15:59       ` Qing Zhao
2022-06-28 16:43         ` Jakub Jelinek
2022-06-28 18:15           ` Qing Zhao
2022-06-28 18:22             ` Jakub Jelinek
2022-06-28 18:29               ` Qing Zhao
2022-06-28 18:49                 ` Jakub Jelinek
2022-06-28 19:01                   ` Qing Zhao
2022-06-29 21:14                     ` Martin Sebor
2022-06-30 14:07                       ` Qing Zhao
2022-06-30 14:24                         ` Richard Biener
2022-06-30 15:31                           ` Qing Zhao
2022-06-30 17:03                             ` Jakub Jelinek
2022-06-30 19:30                               ` Qing Zhao
2022-07-01  6:49                                 ` Richard Biener
2022-07-01 12:55                                   ` Qing Zhao
2022-07-01 12:58                                     ` Richard Biener
2022-07-01 13:40                                       ` Qing Zhao
2022-07-01 12:59                                     ` Jakub Jelinek
2022-07-01 14:01                                       ` Qing Zhao
2022-07-01 15:32                                         ` Martin Sebor
2022-07-04  6:49                                           ` Richard Biener
2022-07-06 14:20                                             ` Qing Zhao [this message]
2022-07-07  8:02                                               ` Richard Biener
2022-07-07 13:33                                                 ` Qing Zhao
2022-06-29 20:45           ` Qing Zhao
2022-06-28 16:21   ` Martin Sebor

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