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From: "Jose E. Marchesi" <jose.marchesi@oracle.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Qing Zhao <qing.zhao@oracle.com>,
	richard Biener <richard.guenther@gmail.com>,
	Joseph Myers <joseph@codesourcery.com>,
	Siddhesh Poyarekar <siddhesh@gotplt.org>,
	Martin Uecker <uecker@tugraz.at>,
	Kees Cook <keescook@chromium.org>,
	"isanbard@gmail.com" <isanbard@gmail.com>,
	GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: RFC (V2) the proposal to resolve the missing dependency issue for counted_by attribute
Date: Thu, 09 Nov 2023 17:50:01 +0100	[thread overview]
Message-ID: <871qcyub0m.fsf@oracle.com> (raw)
In-Reply-To: <ZU0BakPdLWIIobu6@tucnak> (Jakub Jelinek's message of "Thu, 9 Nov 2023 16:57:30 +0100")


> On Thu, Nov 09, 2023 at 03:49:49PM +0000, Qing Zhao wrote:
>> Is it reasonable to add one option to disable the “counted_by” attribute?
>> (then no insertion of the new .ACCESS_WITH_SIZE into IL).  
>> 
>> The major reason is: some users might want to ignore all the “counted_by” attribute added in the source code,
>> We need to provide them a way to disable this feature.
>
> -D'counted_by(x)='
> and/or
> -D'__counted_by__(x)='
> ?

The insertion of .ACCESS_WITH_SIZE collides with the BPF CO-RE
preserve_access_index implementation.

I don't think this will be a problem in practice (the BPF program can
define counted_by to the empty string as Jakub suggests) but we ought to
at least detect when a data structure featuring a counted_by FMA is
accessed with access index preservation (either attribute or builtin)
and either error out or warning out and try to accomodate by turning the
.ACCESS_WTIH_INDEX back to plain accesses.  We can do either with BPF
specific backend code.

  reply	other threads:[~2023-11-09 16:50 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-07  0:12 Qing Zhao
2023-11-09 15:49 ` Qing Zhao
2023-11-09 15:57   ` Jakub Jelinek
2023-11-09 16:50     ` Jose E. Marchesi [this message]
2023-11-09 17:23       ` Qing Zhao

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