From: Matthew Wilcox <willy@infradead.org>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux.com>, Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>
Subject: Re: [GIT PULL] percpu fix for v5.9-rc6
Date: Sat, 19 Sep 2020 03:45:56 +0100 [thread overview]
Message-ID: <20200919024556.GJ32101@casper.infradead.org> (raw)
In-Reply-To: <20200918223957.GA2964553@rani.riverdale.lan>
On Fri, Sep 18, 2020 at 06:39:57PM -0400, Arvind Sankar wrote:
> On Fri, Sep 18, 2020 at 02:18:20PM -0700, Linus Torvalds wrote:
> > On Fri, Sep 18, 2020 at 2:00 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > You could just assert that offsetof(typeof(s),flex) == sizeof(s), no?
> >
> > No, because the whole point is that I want that "sizeof(s)" to *WARN*.
>
> Ouch, offsetof() and sizeof() will give different results in the
> presence of alignment padding.
>
> https://godbolt.org/z/rqnxTK
We really should be using offsetof() then. It's harmless because we're
currently overallocating, not underallocating. The test case I did was:
struct s {
int count;
char *p[];
};
struct_size(&s, p, 5); (48 bytes)
struct_size2(&s, p, 5); (also 48 bytes)
struct_size2 uses offsetof instead of sizeof.
Your case is different because the chars fit in the padding at the end
of the struct.
next prev parent reply other threads:[~2020-09-19 2:46 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-17 20:45 Dennis Zhou
2020-09-18 1:05 ` Linus Torvalds
2020-09-18 16:23 ` Gustavo A. R. Silva
2020-09-18 17:23 ` Linus Torvalds
2020-09-18 19:34 ` Gustavo A. R. Silva
2020-09-18 19:37 ` Linus Torvalds
2020-09-18 20:02 ` Matthew Wilcox
2020-09-18 20:14 ` Linus Torvalds
2020-09-18 20:29 ` Arvind Sankar
2020-09-18 20:40 ` Linus Torvalds
2020-09-18 21:00 ` Arvind Sankar
2020-09-18 21:18 ` Linus Torvalds
2020-09-18 22:39 ` Arvind Sankar
2020-09-19 1:28 ` Linus Torvalds
2020-09-19 2:53 ` Arvind Sankar
2020-09-19 3:02 ` Matthew Wilcox
2020-09-19 3:04 ` Linus Torvalds
2020-09-19 2:45 ` Matthew Wilcox [this message]
2020-09-19 3:37 ` Arvind Sankar
2020-09-19 15:15 ` David Laight
2020-09-18 20:03 ` Gustavo A. R. Silva
2020-09-18 1:10 ` pr-tracker-bot
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