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Message-ID: <CAPhsuW6iicoRN3Sk6Uv-ten4xjjmqG1qmfmXyKngqVSYC9qbEQ@mail.gmail.com>
Date: Sat, 15 Jun 2019 14:07:53 -0700
From: Song Liu <liu.song.a23@...il.com>
To: Andrii Nakryiko <andriin@...com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>,
bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
Kernel Team <kernel-team@...com>
Subject: Re: [RFC PATCH bpf-next 4/8] libbpf: identify maps by section index
in addition to offset
On Mon, Jun 10, 2019 at 9:37 PM Andrii Nakryiko <andriin@...com> wrote:
>
> To support maps to be defined in multiple sections, it's important to
> identify map not just by offset within its section, but section index as
> well. This patch adds tracking of section index.
>
> For global data, we record section index of corresponding
> .data/.bss/.rodata ELF section for uniformity, and thus don't need
> a special value of offset for those maps.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
> tools/lib/bpf/libbpf.c | 42 ++++++++++++++++++++++++++----------------
> 1 file changed, 26 insertions(+), 16 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index c931ee7e1fd2..5e7ea7dac958 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -207,7 +207,8 @@ static const char * const libbpf_type_to_btf_name[] = {
> struct bpf_map {
> int fd;
> char *name;
> - size_t offset;
> + int sec_idx;
> + size_t sec_offset;
> int map_ifindex;
> int inner_map_fd;
> struct bpf_map_def def;
> @@ -647,7 +648,9 @@ static int compare_bpf_map(const void *_a, const void *_b)
> const struct bpf_map *a = _a;
> const struct bpf_map *b = _b;
>
> - return a->offset - b->offset;
> + if (a->sec_idx != b->sec_idx)
> + return a->sec_idx - b->sec_idx;
> + return a->sec_offset - b->sec_offset;
> }
>
> static bool bpf_map_type__is_map_in_map(enum bpf_map_type type)
> @@ -800,14 +803,15 @@ static struct bpf_map *bpf_object__add_map(struct bpf_object *obj)
>
> static int
> bpf_object__init_internal_map(struct bpf_object *obj, struct bpf_map *map,
> - enum libbpf_map_type type, Elf_Data *data,
> - void **data_buff)
> + enum libbpf_map_type type, int sec_idx,
> + Elf_Data *data, void **data_buff)
> {
> struct bpf_map_def *def = &map->def;
> char map_name[BPF_OBJ_NAME_LEN];
>
> map->libbpf_type = type;
> - map->offset = ~(typeof(map->offset))0;
> + map->sec_idx = sec_idx;
> + map->sec_offset = 0;
> snprintf(map_name, sizeof(map_name), "%.8s%.7s", obj->name,
> libbpf_type_to_btf_name[type]);
> map->name = strdup(map_name);
> @@ -815,6 +819,8 @@ bpf_object__init_internal_map(struct bpf_object *obj, struct bpf_map *map,
> pr_warning("failed to alloc map name\n");
> return -ENOMEM;
> }
> + pr_debug("map '%s' (global data): at sec_idx %d, offset %zu.\n",
> + map_name, map->sec_idx, map->sec_offset);
>
> def->type = BPF_MAP_TYPE_ARRAY;
> def->key_size = sizeof(int);
> @@ -850,6 +856,7 @@ static int bpf_object__init_global_data_maps(struct bpf_object *obj)
> if (IS_ERR(map))
> return PTR_ERR(map);
> err = bpf_object__init_internal_map(obj, map, LIBBPF_MAP_DATA,
> + obj->efile.data_shndx,
> obj->efile.data,
> &obj->sections.data);
> if (err)
> @@ -860,6 +867,7 @@ static int bpf_object__init_global_data_maps(struct bpf_object *obj)
> if (IS_ERR(map))
> return PTR_ERR(map);
> err = bpf_object__init_internal_map(obj, map, LIBBPF_MAP_RODATA,
> + obj->efile.rodata_shndx,
> obj->efile.rodata,
> &obj->sections.rodata);
> if (err)
> @@ -870,6 +878,7 @@ static int bpf_object__init_global_data_maps(struct bpf_object *obj)
> if (IS_ERR(map))
> return PTR_ERR(map);
> err = bpf_object__init_internal_map(obj, map, LIBBPF_MAP_BSS,
> + obj->efile.bss_shndx,
> obj->efile.bss, NULL);
> if (err)
> return err;
> @@ -953,7 +962,10 @@ static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
> }
>
> map->libbpf_type = LIBBPF_MAP_UNSPEC;
> - map->offset = sym.st_value;
> + map->sec_idx = sym.st_shndx;
> + map->sec_offset = sym.st_value;
> + pr_debug("map '%s' (legacy): at sec_idx %d, offset %zu.\n",
> + map_name, map->sec_idx, map->sec_offset);
> if (sym.st_value + map_def_sz > data->d_size) {
> pr_warning("corrupted maps section in %s: last map \"%s\" too small\n",
> obj->path, map_name);
> @@ -1453,9 +1465,13 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
> if (maps[map_idx].libbpf_type != type)
> continue;
> if (type != LIBBPF_MAP_UNSPEC ||
> - maps[map_idx].offset == sym.st_value) {
> - pr_debug("relocation: find map %zd (%s) for insn %u\n",
> - map_idx, maps[map_idx].name, insn_idx);
> + (maps[map_idx].sec_idx == sym.st_shndx &&
> + maps[map_idx].sec_offset == sym.st_value)) {
> + pr_debug("relocation: found map %zd (%s, sec_idx %d, offset %zu) for insn %u\n",
> + map_idx, maps[map_idx].name,
> + maps[map_idx].sec_idx,
> + maps[map_idx].sec_offset,
> + insn_idx);
> break;
> }
> }
> @@ -3472,13 +3488,7 @@ bpf_object__find_map_fd_by_name(struct bpf_object *obj, const char *name)
> struct bpf_map *
> bpf_object__find_map_by_offset(struct bpf_object *obj, size_t offset)
> {
> - int i;
> -
> - for (i = 0; i < obj->nr_maps; i++) {
> - if (obj->maps[i].offset == offset)
> - return &obj->maps[i];
> - }
> - return ERR_PTR(-ENOENT);
> + return ERR_PTR(-ENOTSUP);
I probably missed some discussion. But is it OK to stop supporting
this function?
Thanks,
Song
> }
>
> long libbpf_get_error(const void *ptr)
> --
> 2.17.1
>
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