Hi Anthony, Norbert,
Thanks for your patch!
On Thu, Mar 25, 2021 at 11:29 PM Tony Nguyen <anthony.l.ngu...@intel.com> wrote:
> From: Norbert Ciosek <norbertx.cio...@intel.com>
>
> Remove padding from RSS structures. Previous layout
> could lead to unwanted compiler optimizations
> in loops when iterating over key and lut arrays.
>From an earlier private conversation with Mateusz, I understand the real
explanation is that key[] and lut[] must be at the end of the
structures, because they are used as flexible array members?
> Fixes: 65ece6de0114 ("virtchnl: Add missing explicit padding to structures")
> Signed-off-by: Norbert Ciosek <norbertx.cio...@intel.com>
> Tested-by: Konrad Jankowski <konrad0.jankow...@intel.com>
> Signed-off-by: Tony Nguyen <anthony.l.ngu...@intel.com>
> --- a/include/linux/avf/virtchnl.h
> +++ b/include/linux/avf/virtchnl.h
> @@ -476,7 +476,6 @@ struct virtchnl_rss_key {
> u16 vsi_id;
> u16 key_len;
> u8 key[1]; /* RSS hash key, packed bytes */
> - u8 pad[1];
> };
>
> VIRTCHNL_CHECK_STRUCT_LEN(6, virtchnl_rss_key);
> @@ -485,7 +484,6 @@ struct virtchnl_rss_lut {
> u16 vsi_id;
> u16 lut_entries;
> u8 lut[1]; /* RSS lookup table */
> - u8 pad[1];
> };
If you use a flexible array member, it should be declared without a size,
i.e.
u8 key[];
Everything else is (trying to) fool the compiler, and leading to undefined
behavior, and people (re)adding explicit padding.
--
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
