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

[Łukasz Bartosik]

pt., 10 lis 2023 o 22:01 <jim.cromie@xxxxxxxxx> napisał(a):
>
> 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 */

I will test it on arm64.