From: Kees Cook <keescook@chromium.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
linux-api@vger.kernel.org, linux-hardening@vger.kernel.org,
David.Laight@aculab.com
Subject: Re: [PATCH v3 1/2] uapi: fix __DECLARE_FLEX_ARRAY for C++
Date: Fri, 15 Sep 2023 12:14:06 -0700 [thread overview]
Message-ID: <202309151208.C99747375@keescook> (raw)
In-Reply-To: <97242381-f1ec-4a4a-9472-1a464f575657@p183>
On Tue, Sep 12, 2023 at 07:22:24PM +0300, Alexey Dobriyan wrote:
> __DECLARE_FLEX_ARRAY(T, member) macro expands to
>
> struct {
> struct {} __empty_member;
> T member[];
> };
>
> which is subtly wrong in C++ because sizeof(struct{}) is 1 not 0,
> changing UAPI structures layouts.
Looking at this again just now, what about using a 0-length array
instead of an anonymous struct?
https://godbolt.org/z/rGaxPWjef
Then we don't need an #ifdef at all...
struct {
int __empty_member[0];
T member[];
};
-Kees
--
Kees Cook
prev parent reply other threads:[~2023-09-15 19:15 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-08 11:32 [PATCH] uapi: partially fix __DECLARE_FLEX_ARRAY for C++ Alexey Dobriyan
2023-09-08 15:14 ` [PATCH v2] uapi: " Alexey Dobriyan
2023-09-08 15:53 ` Kees Cook
2023-09-08 16:03 ` Alexey Dobriyan
2023-09-08 16:11 ` Kees Cook
2023-09-11 8:19 ` David Laight
2023-09-12 15:06 ` Alexey Dobriyan
2023-09-12 16:22 ` [PATCH v3 1/2] " Alexey Dobriyan
2023-09-12 16:23 ` [PATCH v3 2/2] uapi: fix header guard in include/uapi/linux/stddef.h Alexey Dobriyan
2023-09-15 19:14 ` Kees Cook [this message]
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