(Sorry for the late reply, just came back from a short vacation.)
> On Jul 4, 2022, at 2:49 AM, Richard Biener <[email protected]> wrote:
>
> On Fri, Jul 1, 2022 at 5:32 PM Martin Sebor <[email protected]> wrote:
>>
>> On 7/1/22 08:01, Qing Zhao wrote:
>>>
>>>
>>>> On Jul 1, 2022, at 8:59 AM, Jakub Jelinek <[email protected]> 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
