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| author | Kees Cook <keescook@chromium.org> | 2023-01-06 23:06:04 +0300 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2023-01-13 19:26:19 +0300 |
| commit | 8763a30bc15b36c3bd90d6da7272d972b995f318 (patch) | |
| tree | 3671cecf70a641d4b5dbd130a5d7b9862da15a21 /Documentation/process | |
| parent | 5a37deab42ad1630b39bf9bca13aa55e94310b01 (diff) | |
| download | linux-8763a30bc15b36c3bd90d6da7272d972b995f318.tar.xz | |
docs: deprecated.rst: Add note about DECLARE_FLEX_ARRAY() usage
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: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230106200600.never.735-kees@kernel.org
[jc: minor wording tweaks]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/process')
| -rw-r--r-- | Documentation/process/deprecated.rst | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst index c8fd53a11a20..f91b8441f2ef 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.) Those cases are 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); + }; + }; |