Re: [RFC PATCH] libbpf: Add bpf_program__set_section_name api

[Tao Chen]

Hi, Andrii, thank you for your reply. I read the apis again in libbpf.h, 
as you say, it seems that this patch no need. Thanks again.

在 2024/3/26 上午1:25, Andrii Nakryiko 写道:
> On Mon, Mar 25, 2024 at 8:48 AM Tao Chen <chen.dylane@xxxxxxxxx> wrote:
> > The new api can be used to reset the function we want to trace in
> > runtime. So we need not to change the code again when we just do
> > minor changes to the trace function in kprobe or other ebpf event
> > type. We can replace the old section with new section passed in via
> > parameter. Maybe the following scenario we can use the api:
> >
> > 1. solve "*.isra.o" issue caused by compiler in new kernel
> > obj = offcputime_bpf__open();
> > bpf_program__set_section_name(*(obj->skeleton->obj),
> > "kprobe/finish_task_switch", "kprobe/finish_task_switch.isra.0");
> >
> > 2. dynamic adjustment for trace function offset
> > obj = offcputime_bpf__open();
> > bpf_program__set_section_name(*(obj->skeleton->obj),
> > "kprobe/finish_task_switch+23", "kprobe/finish_task_switch+45");
> >
> > Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> > ---
> >   tools/lib/bpf/libbpf.c   | 24 ++++++++++++++++++++++++
> >   tools/lib/bpf/libbpf.h   |  2 ++
> >   tools/lib/bpf/libbpf.map |  1 +
> >   3 files changed, 27 insertions(+)
>
> This is a wrong approach. SEC() is immutable and serves as a hint to
> libbpf on program type and possibly some attach parameters. But after
> that libbpf allows to override all of them though APIs like
> bpf_program__set_type() and others. Attach APIs always allow to
> specify all the target parameters, including kprobe function name and
> so on.
>
> Please check all of the libbpf APIs in libbpf.h.
>
> pw-bot: cr
>
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 96ff1aa4bf6a..94f32e845c61 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -8576,6 +8576,30 @@ const char *bpf_program__section_name(const struct bpf_program *prog)
> >          return prog->sec_name;
> >   }
>
> [...]