Hi, Sid,
Thanks a lot for the input.
After more thinking based on your and Kees’ comments, I have the following
thought:
1. -fstrict-flex-arrays=level should control both GCC code gen and warnings
consistently;
2. We need warnings specifically for -fstrict-flex-arrays=level to report any
misuse of flexible
array corresponding to the “level” to gradually encourage language
standard.
So, based on the above two, I think what I did in this current patch is correct:
1. We eliminate the control from -Warray-bounds=level on treating flex arrays,
now only "-fstrict-flex-arrasy=level" controls how the warning treating
the flex arrays.
2. We add a separate new warning -Wstrict-flex-arrays to report any misuse
corresponding to
the different level of -fstrict-flex-arrays.
Although we can certainly merge these new warnings into -Warray-bounds,
however, as Sid mentioned,
-Warray-bounds does issue a lot more warnings than just flexible arrays misuse.
I think it’s necessary
To provide a seperate warning to only issue flexible array misuse.
Let me know if you have any more comments on this.
thanks.
Qing
> On Dec 1, 2022, at 2:45 PM, Siddhesh Poyarekar <siddh...@gotplt.org> wrote:
>
> On 2022-12-01 11:42, Kees Cook wrote:
>> On Wed, Nov 30, 2022 at 02:25:56PM +0000, Qing Zhao wrote:
>>> '-Wstrict-flex-arrays'
>>> Warn about inproper usages of flexible array members according to
>>> the LEVEL of the 'strict_flex_array (LEVEL)' attribute attached to
>>> the trailing array field of a structure if it's available,
>>> otherwise according to the LEVEL of the option
>>> '-fstrict-flex-arrays=LEVEL'.
>>>
>>> This option is effective only when LEVEL is bigger than 0.
>>> Otherwise, it will be ignored with a warning.
>>>
>>> when LEVEL=1, warnings will be issued for a trailing array
>>> reference of a structure that have 2 or more elements if the
>>> trailing array is referenced as a flexible array member.
>>>
>>> when LEVEL=2, in addition to LEVEL=1, additional warnings will be
>>> issued for a trailing one-element array reference of a structure if
>>> the array is referenced as a flexible array member.
>>>
>>> when LEVEL=3, in addition to LEVEL=2, additional warnings will be
>>> issued for a trailing zero-length array reference of a structure if
>>> the array is referenced as a flexible array member.
>>>
>>> At the same time, -Warray-bounds is updated:
>> Why is there both -Wstrict-flex-arrays and -Warray-bounds? I thought
>> only the latter was going to exist?
>
> Oh my understanding of the consensus was to move flex array related diagnosis
> from -Warray-bounds to -Wstring-flex-arrays as Qing has done. If only the
> former exists then instead of removing the flex array related statement in
> the documentation as Richard suggested, we need to enhance it to say that
> behaviour of -Warray-bounds will depend on -fstrict-flex-arrays.
>
> -Warray-bounds does diagnosis beyond just flexible arrays, in case that's the
> confusion.
>
> Sid
