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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 Andrii Nakryiko
parent 0141d9dded
commit 3298393748
3 changed files with 280 additions and 58 deletions
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16
src/bpf_gen_internal.h
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@@ -7,6 +7,15 @@ struct ksym_relo_desc {
const char *name;
int kind;
int insn_idx;
bool is_weak;
};
struct ksym_desc {
const char *name;
int ref;
int kind;
int off;
int insn;
};
struct bpf_gen {
@@ -24,6 +33,10 @@ struct bpf_gen {
int relo_cnt;
char attach_target[128];
int attach_kind;
struct ksym_desc *ksyms;
__u32 nr_ksyms;
int fd_array;
int nr_fd_array;
};
void bpf_gen__init(struct bpf_gen *gen, int log_level);
@@ -36,6 +49,7 @@ void bpf_gen__prog_load(struct bpf_gen *gen, struct bpf_prog_load_params *load_a
void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *value, __u32 value_size);
void bpf_gen__map_freeze(struct bpf_gen *gen, int map_idx);
void bpf_gen__record_attach_target(struct bpf_gen *gen, const char *name, enum bpf_attach_type type);
void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, int kind, int insn_idx);
void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak, int kind,
int insn_idx);
#endif