On Mon, Nov 22, 2021 at 4:04 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Fri, Nov 19, 2021 at 7:33 PM Alexei Starovoitov
> <alexei.starovoitov@xxxxxxxxx> wrote:
> >
> > From: Alexei Starovoitov <ast@xxxxxxxxxx>
> >
> > Without lskel the CO-RE relocations are processed by libbpf before any other
> > work is done. Instead, when lskel is needed, remember relocation as RELO_CORE
> > kind. Then when loader prog is generated for a given bpf program pass CO-RE
> > relos of that program to gen loader via bpf_gen__record_relo_core(). The gen
> > loader will remember them as-is and pass it later as-is into the kernel.
> >
> > The normal libbpf flow is to process CO-RE early before call relos happen. In
> > case of gen_loader the core relos have to be added to other relos to be copied
> > together when bpf static function is appended in different places to other main
> > bpf progs. During the copy the append_subprog_relos() will adjust insn_idx for
> > normal relos and for RELO_CORE kind too. When that is done each struct
> > reloc_desc has good relos for specific main prog.
> >
> > Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> > ---
> > tools/lib/bpf/bpf_gen_internal.h | 3 +
> > tools/lib/bpf/gen_loader.c | 41 +++++++++++-
> > tools/lib/bpf/libbpf.c | 108 ++++++++++++++++++++++---------
> > 3 files changed, 119 insertions(+), 33 deletions(-)
> >
>
> [...]
>
> > if (relo->kind != BPF_CORE_TYPE_ID_LOCAL &&
> > @@ -5653,6 +5679,9 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
> > case RELO_CALL:
> > /* handled already */
> > break;
> > + case RELO_CORE:
> > + /* will be handled by bpf_program_record_relos() */
> > + break;
> > default:
> > pr_warn("prog '%s': relo #%d: bad relo type %d\n",
> > prog->name, i, relo->type);
> > @@ -6090,6 +6119,35 @@ bpf_object__free_relocs(struct bpf_object *obj)
> > }
> > }
> >
> > +static int cmp_relocs(const void *_a, const void *_b)
> > +{
> > + const struct reloc_desc *a = _a;
> > + const struct reloc_desc *b = _b;
> > +
> > + if (a->insn_idx != b->insn_idx)
> > + return a->insn_idx < b->insn_idx ? -1 : 1;
> > +
> > + /* no two relocations should have the same insn_idx, but ... */
> > + if (a->type != b->type)
> > + return a->type < b->type ? -1 : 1;
> > +
> > + return 0;
> > +}
> > +
> > +static void bpf_object__sort_relos(struct bpf_object *obj)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < obj->nr_programs; i++) {
> > + struct bpf_program *p = &obj->programs[i];
> > +
> > + if (!p->nr_reloc)
> > + continue;
> > +
> > + qsort(p->reloc_desc, p->nr_reloc, sizeof(*p->reloc_desc), cmp_relocs);
> > + }
> > +}
> > +
> > static int
> > bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
> > {
> > @@ -6104,6 +6162,8 @@ bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
> > err);
> > return err;
> > }
> > + if (obj->gen_loader)
> > + bpf_object__sort_relos(obj);
>
> libbpf sorts relos because it does binary search on them (see
> find_prog_insn_relo).
exactly.
After co-re relos were added the array has to be sorted again.
find_prog_insn_relo() will be called after this step.
