Re: [RFC bpf-next 1/3] libbpf: Support aliased symbols in linker

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Sep 03, 2024 at 03:08:25PM +0200, Viktor Malik wrote:
> On 9/3/24 13:16, Jiri Olsa wrote:
> > On Mon, Sep 02, 2024 at 08:58:01AM +0200, Viktor Malik wrote:
> >> It is possible to create multiple BPF programs sharing the same
> >> instructions using the compiler `__attribute__((alias("...")))`:
> >>
> >>     int BPF_PROG(prog)
> >>     {
> >>         [...]
> >>     }
> >>     int prog_alias() __attribute__((alias("prog")));
> >>
> >> This may be convenient when creating multiple programs with the same
> >> instruction set attached to different events (such as bpftrace does).
> >>
> >> One problem in this situation is that Clang doesn't generate a BTF entry
> >> for `prog_alias` which makes libbpf linker fail when processing such a
> >> BPF object.
> > 
> > this might not solve all the issues, but could we change pahole to
> > generate BTF FUNC for alias function symbols?
> 
> I don't think that would work here. First, we don't usually run pahole
> when building BPF objects, it's Clang which generates BTF for the "bpf"
> target directly. Second, AFAIK, pahole converts DWARF to BTF and
> compilers don't generate DWARF entries for alias function symbols either.

ah ok, sry I misunderstood the purpose.. it's about the bpf code
generated in bpftrace

jirka