On Mon, Dec 06, 2021 at 01:41:15PM -0800, Andrii Nakryiko wrote:
> On Sat, Dec 4, 2021 at 6:07 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > As suggested by Andrii, adding variables for registers and ip
> > address offsets, which makes the code more clear, rather than
> > abusing single stack_size variable for everything.
> >
> > Also describing the stack layout in the comment.
> >
> > There is no function change.
> >
> > Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > arch/x86/net/bpf_jit_comp.c | 42 ++++++++++++++++++++++++-------------
> > 1 file changed, 28 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> > index 1d7b0c69b644..b106e80e8d9c 100644
> > --- a/arch/x86/net/bpf_jit_comp.c
> > +++ b/arch/x86/net/bpf_jit_comp.c
> > @@ -1941,7 +1941,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> > void *orig_call)
> > {
> > int ret, i, nr_args = m->nr_args;
> > - int stack_size = nr_args * 8;
> > + int regs_off, ip_off, stack_size = nr_args * 8;
> > struct bpf_tramp_progs *fentry = &tprogs[BPF_TRAMP_FENTRY];
> > struct bpf_tramp_progs *fexit = &tprogs[BPF_TRAMP_FEXIT];
> > struct bpf_tramp_progs *fmod_ret = &tprogs[BPF_TRAMP_MODIFY_RETURN];
> > @@ -1956,14 +1956,33 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> > if (!is_valid_bpf_tramp_flags(flags))
> > return -EINVAL;
> >
> > + /* Generated trampoline stack layout:
> > + *
> > + * RBP + 8 [ return address ]
> > + * RBP + 0 [ RBP ]
> > + *
> > + * RBP - 8 [ return value ] BPF_TRAMP_F_CALL_ORIG or
> > + * BPF_TRAMP_F_RET_FENTRY_RET flags
> > + *
> > + * [ reg_argN ] always
> > + * [ ... ]
> > + * RBP - regs_off [ reg_arg1 ]
> > + *
>
> I think it's also worth mentioning that context passed into
> fentry/fexit programs are pointing here (makes it a bit easier to
> track those ctx[-1] and ctx[-2] in the next patch.
ok, jirka
>
>
> > + * RBP - ip_off [ traced function ] BPF_TRAMP_F_IP_ARG flag
> > + */
> > +
> > /* room for return value of orig_call or fentry prog */
> > save_ret = flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET);
> > if (save_ret)
> > stack_size += 8;
> >
> > + regs_off = stack_size;
> > +
> > if (flags & BPF_TRAMP_F_IP_ARG)
> > stack_size += 8; /* room for IP address argument */
> >
> > + ip_off = stack_size;
> > +
>
> [...]
>
