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SubjectRe: [PATCH 7/8] tools lib bpf: fix maps resolution
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Hi Eric,

Are you still working in this patch set?

Now I know why maps section is not a simple array
from a patch set from Joe Stringer:

https://www.mail-archive.com/netdev@vger.kernel.org/msg135088.html

So I think this patch is really useful.

Are you going to resend the whole patch set? If not, let me collect
this patch 7/8 into my local code base and send to Arnaldo
with my other patches.

Thank you.

On 2016/10/17 5:18, Eric Leblond wrote:
> It is not correct to assimilate the elf data of the maps section
> to an array of map definition. In fact the sizes differ. The
> offset provided in the symbol section has to be used instead.
>
> This patch fixes a bug causing a elf with two maps not to load
> correctly.
>
> Signed-off-by: Eric Leblond <eric@regit.org>
> ---
> tools/lib/bpf/libbpf.c | 50 +++++++++++++++++++++++++++++++++++---------------
> 1 file changed, 35 insertions(+), 15 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 1fe4532..f72628b 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -186,6 +186,7 @@ struct bpf_program {
> struct bpf_map {
> int fd;
> char *name;
> + size_t offset;
> struct bpf_map_def def;
> void *priv;
> bpf_map_clear_priv_t clear_priv;
> @@ -529,13 +530,6 @@ bpf_object__init_maps(struct bpf_object *obj, void *data,
>
> pr_debug("maps in %s: %zd bytes\n", obj->path, size);
>
> - obj->maps = calloc(nr_maps, sizeof(obj->maps[0]));
> - if (!obj->maps) {
> - pr_warning("alloc maps for object failed\n");
> - return -ENOMEM;
> - }
> - obj->nr_maps = nr_maps;
> -
> for (i = 0; i < nr_maps; i++) {
> struct bpf_map_def *def = &obj->maps[i].def;
>
> @@ -547,23 +541,42 @@ bpf_object__init_maps(struct bpf_object *obj, void *data,
> obj->maps[i].fd = -1;
>
> /* Save map definition into obj->maps */
> - *def = ((struct bpf_map_def *)data)[i];
> + *def = *(struct bpf_map_def *)(data + obj->maps[i].offset);
> }
> return 0;
> }
>
> static int
> -bpf_object__init_maps_name(struct bpf_object *obj)
> +bpf_object__init_maps_symbol(struct bpf_object *obj)
> {
> int i;
> + int nr_maps = 0;
> Elf_Data *symbols = obj->efile.symbols;
> + size_t map_idx = 0;
>
> if (!symbols || obj->efile.maps_shndx < 0)
> return -EINVAL;
>
> + /* get the number of maps */
> + for (i = 0; i < symbols->d_size / sizeof(GElf_Sym); i++) {
> + GElf_Sym sym;
> +
> + if (!gelf_getsym(symbols, i, &sym))
> + continue;
> + if (sym.st_shndx != obj->efile.maps_shndx)
> + continue;
> + nr_maps++;
> + }
> +
> + obj->maps = calloc(nr_maps, sizeof(obj->maps[0]));
> + if (!obj->maps) {
> + pr_warning("alloc maps for object failed\n");
> + return -ENOMEM;
> + }
> + obj->nr_maps = nr_maps;
> +
> for (i = 0; i < symbols->d_size / sizeof(GElf_Sym); i++) {
> GElf_Sym sym;
> - size_t map_idx;
> const char *map_name;
>
> if (!gelf_getsym(symbols, i, &sym))
> @@ -574,12 +587,12 @@ bpf_object__init_maps_name(struct bpf_object *obj)
> map_name = elf_strptr(obj->efile.elf,
> obj->efile.strtabidx,
> sym.st_name);
> - map_idx = sym.st_value / sizeof(struct bpf_map_def);
> if (map_idx >= obj->nr_maps) {
> pr_warning("index of map \"%s\" is buggy: %zu > %zu\n",
> map_name, map_idx, obj->nr_maps);
> continue;
> }
> + obj->maps[map_idx].offset = sym.st_value;
> obj->maps[map_idx].name = strdup(map_name);
> if (!obj->maps[map_idx].name) {
> pr_warning("failed to alloc map name\n");
> @@ -587,6 +600,7 @@ bpf_object__init_maps_name(struct bpf_object *obj)
> }
> pr_debug("map %zu is \"%s\"\n", map_idx,
> obj->maps[map_idx].name);
> + map_idx++;
> }
> return 0;
> }
> @@ -647,8 +661,6 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> data->d_buf,
> data->d_size);
> else if (strcmp(name, "maps") == 0) {
> - err = bpf_object__init_maps(obj, data->d_buf,
> - data->d_size);
> obj->efile.maps_shndx = idx;
> } else if (sh.sh_type == SHT_SYMTAB) {
> if (obj->efile.symbols) {
> @@ -698,8 +710,16 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
> pr_warning("Corrupted ELF file: index of strtab invalid\n");
> return LIBBPF_ERRNO__FORMAT;
> }
> - if (obj->efile.maps_shndx >= 0)
> - err = bpf_object__init_maps_name(obj);
> + if (obj->efile.maps_shndx >= 0) {
> + Elf_Data *data;
> + err = bpf_object__init_maps_symbol(obj);
> + if (err)
> + goto out;
> +
> + scn = elf_getscn(elf, obj->efile.maps_shndx);
> + data = elf_getdata(scn, 0);
> + err = bpf_object__init_maps(obj, data->d_buf, data->d_size);
> + }
> out:
> return err;
> }


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