From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id C3EF63858439; Wed,  8 Mar 2023 19:20:09 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C3EF63858439
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1678303209;
	bh=yDGaRGv0yWu3HMfHKIc+2IzgrTCTuL/iDsj2I1JFvPs=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=i/6CDKQbFy90HqxLnbWnyxkUhVWCoaWucaSA8bMurFLUyEJjuaMptSxUD/ZLQlgrn
	 +fzqmX4slzSUSt/Q40LqQZEKoTaarQsfF0A5L0b+AIYYkm5BEfF3yvit+QeeOziQq4
	 MS6m0ykXpVoqHgrhDNRb0sMiSaXqLqxhIXBH9kaw=
From: "qinzhao at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/108896] provide "element_count" attribute to give more
 context to __builtin_dynamic_object_size() and -fsanitize=bounds
Date: Wed, 08 Mar 2023 19:20:09 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: unknown
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: qinzhao at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: qinzhao at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-108896-4-hJpo7eBhrk@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-108896-4@http.gcc.gnu.org/bugzilla/>
References: <bug-108896-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108896

--- Comment #30 from qinzhao at gcc dot gnu.org ---
(In reply to Martin Uecker from comment #28)

> The problems with VLA are in my opinion caused by poor
> implementation (e.g. no stack probing etc) and bad
> code generation (Linus was not happy about this) and
> not because anything is fundamentally bad about them
> from the point of language semantics.

you mean gcc's implementation? how about other compilers?

> VM =3D variably modified.  In C it is a type which is derived from
> a VLA which is not necessarily itself a VLA, e.g. a pointer to
> a VLA. But a VLA is also a VM type.

Okay.
>=20
> > struct foo {
> >   int len;
> >   char (*buf)[.len];
> > };
> >=20
> >=20
> > This has less issues because the size of the struct then does not depend
> > on the length.

but I am still not clear on why "the size of the above struct 'foo' does not
depend on the .len?"  in my opinion, it should depend on .len. do I miss
anything here?=