From: Kees Cook <keescook@chromium.org>
To: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <keescook@chromium.org>,
Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: [PATCH] docs: deprecated.rst: Add note about DECLARE_FLEX_ARRAY() usage
Date: Fri, 6 Jan 2023 12:06:04 -0800 [thread overview]
Message-ID: <20230106200600.never.735-kees@kernel.org> (raw)
There wasn't any mention of when/where DECLARE_FLEX_ARRAY() should be
used, so add the rationale and an example to the deprecation docs.
Suggested-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
Documentation/process/deprecated.rst | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
index c8fd53a11a20..fcac0a929efa 100644
--- a/Documentation/process/deprecated.rst
+++ b/Documentation/process/deprecated.rst
@@ -346,3 +346,29 @@ struct_size() and flex_array_size() helpers::
instance->count = count;
memcpy(instance->items, source, flex_array_size(instance, items, instance->count));
+
+There are two special cases of replacement where the DECLARE_FLEX_ARRAY()
+helper needs to be used. (Note that it is named __DECLARE_FLEX_ARRAY() for
+use in UAPI headers.) When the flexible array is either alone in a struct,
+or is part of a union. These are disallowed by the C99 specification,
+but for no technical reason (as can be seen by both the existing use of
+such arrays in those places and the work-around that DECLARE_FLEX_ARRAY()
+uses). For example, to convert this::
+
+ struct something {
+ ...
+ union {
+ struct type1 one[0];
+ struct type2 two[0];
+ };
+ };
+
+The helper must be used::
+
+ struct something {
+ ...
+ union {
+ DECLARE_FLEX_ARRAY(struct type1, one);
+ DECLARE_FLEX_ARRAY(struct type2, two);
+ };
+ };
--
2.34.1
next reply other threads:[~2023-01-06 20:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-06 20:06 Kees Cook [this message]
2023-01-11 23:11 ` [PATCH] docs: deprecated.rst: Add note about DECLARE_FLEX_ARRAY() usage Jonathan Corbet
2023-01-12 19:38 ` Kees Cook
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20230106200600.never.735-kees@kernel.org \
--to=keescook@chromium.org \
--cc=corbet@lwn.net \
--cc=gustavoars@kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mailhol.vincent@wanadoo.fr \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).