Re: [PATCH 04/64] stddef: Introduce struct_group() helper macro

Rasmus Villemoes
2021-07-28T10:54:26Z

On 27/07/2021 22.57, Kees Cook wrote:

> In order to have a regular programmatic way to describe a struct
> region that can be used for references and sizing, can be examined for
> bounds checking, avoids forcing the use of intermediate identifiers,
> and avoids polluting the global namespace, introduce the struct_group()
> macro. This macro wraps the member declarations to create an anonymous
> union of an anonymous struct (no intermediate name) and a named struct
> (for references and sizing):
>
> struct foo {
> int one;
> struct_group(thing,
> int two,
> int three,
> );
> int four;
> };

That example won't compile, the commas after two and three should be
semicolons.

And your implementation relies on MEMBERS not containing any comma
tokens, but as

int a, b, c, d;

is a valid way to declare multiple members, consider making MEMBERS
variadic

#define struct_group(NAME, MEMBERS...)

to have it slurp up every subsequent argument and make that work.

>
> Co-developed-by: Keith Packard <keithpac@amazon.com>
> Signed-off-by: Keith Packard <keithpac@amazon.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> include/linux/stddef.h | 34 ++++++++++++++++++++++++++++++++++

Bikeshedding a bit, but do we need to add 34 lines that need to be
preprocessed to virtually each and every translation unit [as opposed to
adding a struct_group.h header]? Oh well, you need it for struct
skbuff.h, so it would be pulled in by a lot regardless :(

Rasmus