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libbpf: Update gen_loader to emit BTF_KIND_FUNC relocations

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This change updates the BPF syscall loader to relocate BTF_KIND_FUNC
relocations, with support for weak kfunc relocations. The general idea
is to move map_fds to loader map, and also use the data for storing
kfunc BTF fds. Since both reuse the fd_array parameter, they need to be
kept together.

For map_fds, we reserve MAX_USED_MAPS slots in a region, and for kfunc,
we reserve MAX_KFUNC_DESCS. This is done so that insn->off has more
chances of being <= INT16_MAX than treating data map as a sparse array
and adding fd as needed.

When the MAX_KFUNC_DESCS limit is reached, we fall back to the sparse
array model, so that as long as it does remain <= INT16_MAX, we pass an
index relative to the start of fd_array.

We store all ksyms in an array where we try to avoid calling the
bpf_btf_find_by_name_kind helper, and also reuse the BTF fd that was
already stored. This also speeds up the loading process compared to
emitting calls in all cases, in later tests.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-9-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi
2021-10-02 06:47:56 +05:30
committed by Alexei Starovoitov
parent 466b2e1397
commit 18f4fccbf3
3 changed files with 280 additions and 58 deletions
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8
tools/lib/bpf/libbpf.c
View File

@@ -6360,12 +6360,12 @@ static int bpf_program__record_externs(struct bpf_program *prog)
ext->name);
return -ENOTSUP;
}
bpf_gen__record_extern(obj->gen_loader, ext->name, BTF_KIND_VAR,
relo->insn_idx);
bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
BTF_KIND_VAR, relo->insn_idx);
break;
case RELO_EXTERN_FUNC:
bpf_gen__record_extern(obj->gen_loader, ext->name, BTF_KIND_FUNC,
relo->insn_idx);
bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
BTF_KIND_FUNC, relo->insn_idx);
break;
default:
continue;