On Tue, 2024-07-09 at 16:42 -0700, Andrii Nakryiko wrote:
[...]
> > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> > index 2b54e25d2364..735ae0901b3d 100644
> > --- a/include/linux/bpf_verifier.h
> > +++ b/include/linux/bpf_verifier.h
> > @@ -585,6 +585,15 @@ struct bpf_insn_aux_data {
> > * accepts callback function as a parameter.
> > */
> > bool calls_callback;
> > + /* true if STX or LDX instruction is a part of a spill/fill
> > + * pattern for a no_caller_saved_registers call.
> > + */
> > + u8 nocsr_pattern:1;
> > + /* for CALL instructions, a number of spill/fill pairs in the
> > + * no_caller_saved_registers pattern.
> > + */
> > + u8 nocsr_spills_num:3;
>
> despite bitfields this will extend bpf_insn_aux_data by 8 bytes. there
> are 2 bytes of padding after alu_state, let's put this there.
>
> And let's not add bitfields unless absolutely necessary (this can be
> always done later).
Unfortunately the bitfields are still necessary, here is pahole output
after moving fields and removing bitfields:
struct bpf_insn_aux_data {
...
u8 alu_state; /* 62 1 */
u8 nocsr_pattern; /* 63 1 */
/* --- cacheline 1 boundary (64 bytes) --- */
u8 nocsr_spills_num; /* 64 1 */
/* XXX 3 bytes hole, try to pack */
unsigned int orig_idx; /* 68 4 */
...
/* size: 80, cachelines: 2, members: 20 */
/* sum members: 73, holes: 1, sum holes: 3 */
/* padding: 4 */
/* last cacheline: 16 bytes */
};
While with bitfields:
/* size: 72, cachelines: 2, members: 20 */
[...]
