Re: [PATCH v1 07/12] dyndbg: repack struct _ddebug

[jim . cromie]

On Fri, Nov 10, 2023 at 7:51 AM Łukasz Bartosik <lb@xxxxxxxxxxxx> wrote:
>
> sob., 4 lis 2023 o 02:49 <jim.cromie@xxxxxxxxx> napisał(a):
> >
> > On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@xxxxxxxxxxxx> wrote:
> > >
> > > From: Jim Cromie <jim.cromie@xxxxxxxxx>
> > >
> > > Move the JUMP_LABEL to the top of the struct, since theyre both
> > > align(8) and this closes a pahole (unfortunately trading for padding,
> > > but still).
> > >
> > > Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
> >
> > let me add, I havent really tested this, nevermind thorough.
> > specifically, I didnt look for any offset dependence on the static-key
> > inside their container.
> > Conversely, maybe theres a free default or something in there.
> >
>
> Any idea how to properly test the relocation of the key ?

I was hoping Jason knew it from memory.

I have booted dd-kitchen-sink, which includes it, and it didnt melt the box.

I just checked `pahole vmlinux` output for the existence of 0-offset keys.
Its not conclusive, cuz im only looking at x86.

it does occur, but only for "sub-types".

struct static_key_true {
        struct static_key          key;                  /*     0    16 */

        /* size: 16, cachelines: 1, members: 1 */
        /* last cacheline: 16 bytes */
};
struct static_key_false {
        struct static_key          key;                  /*     0    16 */

        /* size: 16, cachelines: 1, members: 1 */
        /* last cacheline: 16 bytes */
};
struct static_key_false_deferred {
        struct static_key_false    key;                  /*     0    16 */
...};
struct static_key_mod {
        struct static_key_mod *    next;                 /*     0     8 */
...};
struct static_key_deferred {
        struct static_key          key;                  /*     0    16 */