Re: [PATCH][next] stddef: Introduce struct_group_tagged_attr() helper macro

[Gustavo A. R. Silva]

On 3/18/24 17:53, Kees Cook wrote:
> On Mon, Mar 18, 2024 at 05:00:33PM -0600, Gustavo A. R. Silva wrote:
> > We need a new `struct_group()` helper that allows for both having the
> > struct be tagged, and specifying struct attributes like `__packed`
> > or `__align(x)`.
> >
> > This new helper will initially be used to address
> > -Wflex-array-member-not-at-end warnings, where a tagged struct is used
> > to separate the flexible-array member from the rest of the members in
> > the flexible structure [1]. There are some scenarios in which those
> > members need to be packed, as well.
> >
> > So, `struct_group_tagged_attr()` is introduced for this.
> >
> > Link: https://lore.kernel.org/linux-hardening/ZeIgeZ5Sb0IZTOyt@neat/ [1]
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > ---
> >   include/linux/stddef.h | 20 ++++++++++++++++++++
> >   1 file changed, 20 insertions(+)
> >
> > diff --git a/include/linux/stddef.h b/include/linux/stddef.h
> > index 929d67710cc5..919df9453257 100644
> > --- a/include/linux/stddef.h
> > +++ b/include/linux/stddef.h
> > @@ -80,6 +80,26 @@ enum {
> >   #define struct_group_tagged(TAG, NAME, MEMBERS...) \
> >   	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
> >   
> > +/**
> > + * struct_group_tagged_attr() - Create a struct_group with a reusable
> > + * tag and trailing attributes.
> > + *
> > + * @TAG: The tag name for the named sub-struct
> > + * @NAME: The identifier name of the mirrored sub-struct
> > + * @ATTRS: Any struct attributes to apply
> > + * @MEMBERS: The member declarations for the mirrored structs
> > + *
> > + * Used to create an anonymous union of two structs with identical
> > + * layout and size: one anonymous and one named. The former can be
> > + * used normally without sub-struct naming, and the latter can be
> > + * used to reason about the start, end, and size of the group of
> > + * struct members. Includes struct tag argument for the named copy,
> > + * so the specified layout can be reused later. Also includes
> > + * structure attributes argument.
> > + */
> > +#define struct_group_tagged_attr(TAG, NAME, ATTRS, MEMBERS...) \
> > +	__struct_group(TAG, NAME, ATTRS, MEMBERS)
>
> This is the same as __struct_group() only with a longer name? Why not
> just use __struct_group() directly?

Mmmh, the rest of the helpers in the struct_group() family fall in this
same category, can we use __struct_group() indistinctly?

--
Gustavo