On Fri, Feb 18, 2022 at 10:01:45AM +0100, Jiri Olsa wrote:
> On Thu, Feb 17, 2022 at 01:53:16PM -0800, Andrii Nakryiko wrote:
> > On Thu, Feb 17, 2022 at 5:19 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> > >
> > > Some functions we use now for bpf prologue generation are
> > > going to be deprecated, so reworking the current code not
> > > to use them.
> > >
> > > We need to replace following functions/struct:
> > > bpf_program__set_prep
> > > bpf_program__nth_fd
> > > struct bpf_prog_prep_result
> > >
> > > Current code uses bpf_program__set_prep to hook perf callback
> > > before the program is loaded and provide new instructions with
> > > the prologue.
> > >
> > > We workaround this by using objects's 'unloaded' programs instructions
> > > for that specific program and load new ebpf programs with prologue
> > > using separate bpf_prog_load calls.
> > >
> > > We keep new ebpf program instances descriptors in bpf programs
> > > private struct.
> > >
> > > Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > > ---
> > > tools/perf/util/bpf-loader.c | 122 +++++++++++++++++++++++++++++------
> > > 1 file changed, 104 insertions(+), 18 deletions(-)
> > >
> >
> > [...]
> >
> > > errout:
> > > @@ -696,7 +718,7 @@ static int hook_load_preprocessor(struct bpf_program *prog)
> > > struct bpf_prog_priv *priv = program_priv(prog);
> > > struct perf_probe_event *pev;
> > > bool need_prologue = false;
> > > - int err, i;
> > > + int i;
> > >
> > > if (IS_ERR_OR_NULL(priv)) {
> > > pr_debug("Internal error when hook preprocessor\n");
> > > @@ -727,6 +749,12 @@ static int hook_load_preprocessor(struct bpf_program *prog)
> > > return 0;
> > > }
> > >
> > > + /*
> > > + * Do not load programs that need prologue, because we need
> > > + * to add prologue first, check bpf_object__load_prologue.
> > > + */
> > > + bpf_program__set_autoload(prog, false);
> >
> > if you set autoload to false, program instructions might be invalid in
> > the end. Libbpf doesn't apply some (all?) relocations to such
> > programs, doesn't resolve CO-RE, etc, etc. You have to let
> > "prototypal" BPF program to be loaded before you can grab final
> > instructions. It's not great, but in your case it should work, right?
>
> hum, do we care? it should all be done when the 'new' program with
> the prologue is loaded, right?
>
> I switched it off because the verifier failed to load the program
> without the prologue.. because in the originaal program there's no
> code to grab the arguments that the rest of the code depends on,
> so the verifier sees invalid access
>
> >
> > > +
> > > priv->need_prologue = true;
> > > priv->insns_buf = malloc(sizeof(struct bpf_insn) * BPF_MAXINSNS);
> > > if (!priv->insns_buf) {
> > > @@ -734,6 +762,13 @@ static int hook_load_preprocessor(struct bpf_program *prog)
> > > return -ENOMEM;
> > > }
> > >
> >
> > [...]
> >
> > > + /*
> > > + * For each program that needs prologue we do following:
> > > + *
> > > + * - take its current instructions and use them
> > > + * to generate the new code with prologue
> > > + *
> > > + * - load new instructions with bpf_prog_load
> > > + * and keep the fd in proglogue_fds
> > > + *
> > > + * - new fd will be used bpf__foreach_event
> > > + * to connect this program with perf evsel
> > > + */
> > > + orig_insns = bpf_program__insns(prog);
> > > + orig_insns_cnt = bpf_program__insn_cnt(prog);
> > > +
> > > + pev = &priv->pev;
> > > + for (i = 0; i < pev->ntevs; i++) {
> > > + err = preproc_gen_prologue(prog, i, orig_insns,
> > > + orig_insns_cnt, &res);
> > > + if (err)
> > > + return err;
> > > +
> > > + fd = bpf_prog_load(bpf_program__get_type(prog),
> >
> > nit: bpf_program__type() is preferred (we are deprecating/discouraging
> > "get_" prefixed getters in libbpf 1.0)
>
> ok, will change
hum, I can't see bpf_program__type.. what do I miss?
jirka
