Re: [PATCH 02/13] kprobe: Keep traced function address

Jiri Olsa
2022-01-06T08:31:47Z

On Wed, Jan 05, 2022 at 08:30:48PM -0800, Andrii Nakryiko wrote:
> On Tue, Jan 4, 2022 at 12:10 AM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > The bpf_get_func_ip_kprobe helper should return traced function
> > address, but it's doing so only for kprobes that are placed on
> > the function entry.
> >
> > If kprobe is placed within the function, bpf_get_func_ip_kprobe
> > returns that address instead of function entry.
> >
> > Storing the function entry directly in kprobe object, so it could
> > be used in bpf_get_func_ip_kprobe helper.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > include/linux/kprobes.h | 3 +++
> > kernel/kprobes.c | 12 ++++++++++++
> > kernel/trace/bpf_trace.c | 2 +-
> > tools/testing/selftests/bpf/progs/get_func_ip_test.c | 4 ++--
> > 4 files changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> > index 8c8f7a4d93af..a204df4fef96 100644
> > --- a/include/linux/kprobes.h
> > +++ b/include/linux/kprobes.h
> > @@ -74,6 +74,9 @@ struct kprobe {
> > /* Offset into the symbol */
> > unsigned int offset;
> >
> > + /* traced function address */
> > + unsigned long func_addr;
> > +
>
> keep in mind that we'll also need (maybe in a follow up series) to
> store bpf_cookie somewhere close to this func_addr as well. Just
> mentioning to keep in mind as you decide with Masami where to put it.

ok

SNIP

> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 21aa30644219..25631253084a 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1026,7 +1026,7 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> > {
> > struct kprobe *kp = kprobe_running();
> >
> > - return kp ? (uintptr_t)kp->addr : 0;
> > + return kp ? (uintptr_t)kp->func_addr : 0;
> > }
> >
> > static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
> > diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > index a587aeca5ae0..e988aefa567e 100644
> > --- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > +++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > @@ -69,7 +69,7 @@ int test6(struct pt_regs *ctx)
> > {
> > __u64 addr = bpf_get_func_ip(ctx);
> >
> > - test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
> > + test6_result = (const void *) addr == &bpf_fentry_test6;
> > return 0;
> > }
> >
> > @@ -79,6 +79,6 @@ int test7(struct pt_regs *ctx)
> > {
> > __u64 addr = bpf_get_func_ip(ctx);
> >
> > - test7_result = (const void *) addr == &bpf_fentry_test7 + 5;
> > + test7_result = (const void *) addr == &bpf_fentry_test7;
>
> we can treat this as a bug fix for bpf_get_func_ip() for kprobes,
> right? I think "Fixes: " tag is in order then.

true, will add that in next version

thanks,
jirka