Re: [PATCH v2 bpf-next 04/11] libbpf: refactor map initialization

[Matt Hart <matthew.hart@linaro.org>]

Hi all,

I noticed perf fails to build for armv7 on linux next, due to this
compile error:
$ make -C tools/perf ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-

  CC       libbpf_probes.o
In file included from libbpf.c:27:
libbpf.c: In function ‘bpf_object__add_map’:
/home/matt/git/linux-next/tools/include/linux/kernel.h:45:17: error:
comparison of distinct pointer types lacks a cast [-Werror]
  (void) (&_max1 == &_max2);  \
                 ^~
libbpf.c:776:12: note: in expansion of macro ‘max’
  new_cap = max(4ul, obj->maps_cap * 3 / 2);
            ^~~

So I bisected it and came down to this patch.
Commit bf82927125dd25003d76ed5541da704df21de57a

Full verbose bisect script https://hastebin.com/odoyujofav.coffeescript

Is this a case that perf code needs updating to match the change, or
is the change broken?



On Tue, 25 Jun 2019 at 16:53, Andrii Nakryiko <andriin@fb.com> wrote:
>
> User and global data maps initialization has gotten pretty complicated
> and unnecessarily convoluted. This patch splits out the logic for global
> data map and user-defined map initialization. It also removes the
> restriction of pre-calculating how many maps will be initialized,
> instead allowing to keep adding new maps as they are discovered, which
> will be used later for BTF-defined map definitions.
>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ---
>  tools/lib/bpf/libbpf.c | 247 ++++++++++++++++++++++-------------------
>  1 file changed, 133 insertions(+), 114 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 7ee44d8877c5..88609dca4f7d 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -234,6 +234,7 @@ struct bpf_object {
>         size_t nr_programs;
>         struct bpf_map *maps;
>         size_t nr_maps;
> +       size_t maps_cap;
>         struct bpf_secdata sections;
>
>         bool loaded;
> @@ -763,21 +764,51 @@ int bpf_object__variable_offset(const struct bpf_object *obj, const char *name,
>         return -ENOENT;
>  }
>
> -static bool bpf_object__has_maps(const struct bpf_object *obj)
> +static struct bpf_map *bpf_object__add_map(struct bpf_object *obj)
>  {
> -       return obj->efile.maps_shndx >= 0 ||
> -              obj->efile.data_shndx >= 0 ||
> -              obj->efile.rodata_shndx >= 0 ||
> -              obj->efile.bss_shndx >= 0;
> +       struct bpf_map *new_maps;
> +       size_t new_cap;
> +       int i;
> +
> +       if (obj->nr_maps < obj->maps_cap)
> +               return &obj->maps[obj->nr_maps++];
> +
> +       new_cap = max(4ul, obj->maps_cap * 3 / 2);
> +       new_maps = realloc(obj->maps, new_cap * sizeof(*obj->maps));
> +       if (!new_maps) {
> +               pr_warning("alloc maps for object failed\n");
> +               return ERR_PTR(-ENOMEM);
> +       }
> +
> +       obj->maps_cap = new_cap;
> +       obj->maps = new_maps;
> +
> +       /* zero out new maps */
> +       memset(obj->maps + obj->nr_maps, 0,
> +              (obj->maps_cap - obj->nr_maps) * sizeof(*obj->maps));
> +       /*
> +        * fill all fd with -1 so won't close incorrect fd (fd=0 is stdin)
> +        * when failure (zclose won't close negative fd)).
> +        */
> +       for (i = obj->nr_maps; i < obj->maps_cap; i++) {
> +               obj->maps[i].fd = -1;
> +               obj->maps[i].inner_map_fd = -1;
> +       }
> +
> +       return &obj->maps[obj->nr_maps++];
>  }
>
>  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)
> +bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> +                             Elf_Data *data, void **data_buff)
>  {
> -       struct bpf_map_def *def = &map->def;
>         char map_name[BPF_OBJ_NAME_LEN];
> +       struct bpf_map_def *def;
> +       struct bpf_map *map;
> +
> +       map = bpf_object__add_map(obj);
> +       if (IS_ERR(map))
> +               return PTR_ERR(map);
>
>         map->libbpf_type = type;
>         map->offset = ~(typeof(map->offset))0;
> @@ -789,6 +820,7 @@ bpf_object__init_internal_map(struct bpf_object *obj, struct bpf_map *map,
>                 return -ENOMEM;
>         }
>
> +       def = &map->def;
>         def->type = BPF_MAP_TYPE_ARRAY;
>         def->key_size = sizeof(int);
>         def->value_size = data->d_size;
> @@ -808,29 +840,58 @@ bpf_object__init_internal_map(struct bpf_object *obj, struct bpf_map *map,
>         return 0;
>  }
>
> -static int bpf_object__init_maps(struct bpf_object *obj, int flags)
> +static int bpf_object__init_global_data_maps(struct bpf_object *obj)
> +{
> +       int err;
> +
> +       if (!obj->caps.global_data)
> +               return 0;
> +       /*
> +        * Populate obj->maps with libbpf internal maps.
> +        */
> +       if (obj->efile.data_shndx >= 0) {
> +               err = bpf_object__init_internal_map(obj, LIBBPF_MAP_DATA,
> +                                                   obj->efile.data,
> +                                                   &obj->sections.data);
> +               if (err)
> +                       return err;
> +       }
> +       if (obj->efile.rodata_shndx >= 0) {
> +               err = bpf_object__init_internal_map(obj, LIBBPF_MAP_RODATA,
> +                                                   obj->efile.rodata,
> +                                                   &obj->sections.rodata);
> +               if (err)
> +                       return err;
> +       }
> +       if (obj->efile.bss_shndx >= 0) {
> +               err = bpf_object__init_internal_map(obj, LIBBPF_MAP_BSS,
> +                                                   obj->efile.bss, NULL);
> +               if (err)
> +                       return err;
> +       }
> +       return 0;
> +}
> +
> +static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
>  {
> -       int i, map_idx, map_def_sz = 0, nr_syms, nr_maps = 0, nr_maps_glob = 0;
> -       bool strict = !(flags & MAPS_RELAX_COMPAT);
>         Elf_Data *symbols = obj->efile.symbols;
> +       int i, map_def_sz = 0, nr_maps = 0, nr_syms;
>         Elf_Data *data = NULL;
> -       int ret = 0;
> +       Elf_Scn *scn;
> +
> +       if (obj->efile.maps_shndx < 0)
> +               return 0;
>
>         if (!symbols)
>                 return -EINVAL;
> -       nr_syms = symbols->d_size / sizeof(GElf_Sym);
> -
> -       if (obj->efile.maps_shndx >= 0) {
> -               Elf_Scn *scn = elf_getscn(obj->efile.elf,
> -                                         obj->efile.maps_shndx);
>
> -               if (scn)
> -                       data = elf_getdata(scn, NULL);
> -               if (!scn || !data) {
> -                       pr_warning("failed to get Elf_Data from map section %d\n",
> -                                  obj->efile.maps_shndx);
> -                       return -EINVAL;
> -               }
> +       scn = elf_getscn(obj->efile.elf, obj->efile.maps_shndx);
> +       if (scn)
> +               data = elf_getdata(scn, NULL);
> +       if (!scn || !data) {
> +               pr_warning("failed to get Elf_Data from map section %d\n",
> +                          obj->efile.maps_shndx);
> +               return -EINVAL;
>         }
>
>         /*
> @@ -840,16 +901,8 @@ static int bpf_object__init_maps(struct bpf_object *obj, int flags)
>          *
>          * TODO: Detect array of map and report error.
>          */
> -       if (obj->caps.global_data) {
> -               if (obj->efile.data_shndx >= 0)
> -                       nr_maps_glob++;
> -               if (obj->efile.rodata_shndx >= 0)
> -                       nr_maps_glob++;
> -               if (obj->efile.bss_shndx >= 0)
> -                       nr_maps_glob++;
> -       }
> -
> -       for (i = 0; data && i < nr_syms; i++) {
> +       nr_syms = symbols->d_size / sizeof(GElf_Sym);
> +       for (i = 0; i < nr_syms; i++) {
>                 GElf_Sym sym;
>
>                 if (!gelf_getsym(symbols, i, &sym))
> @@ -858,79 +911,56 @@ static int bpf_object__init_maps(struct bpf_object *obj, int flags)
>                         continue;
>                 nr_maps++;
>         }
> -
> -       if (!nr_maps && !nr_maps_glob)
> -               return 0;
> -
>         /* Assume equally sized map definitions */
> -       if (data) {
> -               pr_debug("maps in %s: %d maps in %zd bytes\n", obj->path,
> -                        nr_maps, data->d_size);
> -
> -               map_def_sz = data->d_size / nr_maps;
> -               if (!data->d_size || (data->d_size % nr_maps) != 0) {
> -                       pr_warning("unable to determine map definition size "
> -                                  "section %s, %d maps in %zd bytes\n",
> -                                  obj->path, nr_maps, data->d_size);
> -                       return -EINVAL;
> -               }
> -       }
> -
> -       nr_maps += nr_maps_glob;
> -       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++) {
> -               /*
> -                * fill all fd with -1 so won't close incorrect
> -                * fd (fd=0 is stdin) when failure (zclose won't close
> -                * negative fd)).
> -                */
> -               obj->maps[i].fd = -1;
> -               obj->maps[i].inner_map_fd = -1;
> +       pr_debug("maps in %s: %d maps in %zd bytes\n",
> +                obj->path, nr_maps, data->d_size);
> +
> +       map_def_sz = data->d_size / nr_maps;
> +       if (!data->d_size || (data->d_size % nr_maps) != 0) {
> +               pr_warning("unable to determine map definition size "
> +                          "section %s, %d maps in %zd bytes\n",
> +                          obj->path, nr_maps, data->d_size);
> +               return -EINVAL;
>         }
>
> -       /*
> -        * Fill obj->maps using data in "maps" section.
> -        */
> -       for (i = 0, map_idx = 0; data && i < nr_syms; i++) {
> +       /* Fill obj->maps using data in "maps" section.  */
> +       for (i = 0; i < nr_syms; i++) {
>                 GElf_Sym sym;
>                 const char *map_name;
>                 struct bpf_map_def *def;
> +               struct bpf_map *map;
>
>                 if (!gelf_getsym(symbols, i, &sym))
>                         continue;
>                 if (sym.st_shndx != obj->efile.maps_shndx)
>                         continue;
>
> -               map_name = elf_strptr(obj->efile.elf,
> -                                     obj->efile.strtabidx,
> +               map = bpf_object__add_map(obj);
> +               if (IS_ERR(map))
> +                       return PTR_ERR(map);
> +
> +               map_name = elf_strptr(obj->efile.elf, obj->efile.strtabidx,
>                                       sym.st_name);
>                 if (!map_name) {
>                         pr_warning("failed to get map #%d name sym string for obj %s\n",
> -                                  map_idx, obj->path);
> +                                  i, obj->path);
>                         return -LIBBPF_ERRNO__FORMAT;
>                 }
>
> -               obj->maps[map_idx].libbpf_type = LIBBPF_MAP_UNSPEC;
> -               obj->maps[map_idx].offset = sym.st_value;
> +               map->libbpf_type = LIBBPF_MAP_UNSPEC;
> +               map->offset = sym.st_value;
>                 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);
>                         return -EINVAL;
>                 }
>
> -               obj->maps[map_idx].name = strdup(map_name);
> -               if (!obj->maps[map_idx].name) {
> +               map->name = strdup(map_name);
> +               if (!map->name) {
>                         pr_warning("failed to alloc map name\n");
>                         return -ENOMEM;
>                 }
> -               pr_debug("map %d is \"%s\"\n", map_idx,
> -                        obj->maps[map_idx].name);
> +               pr_debug("map %d is \"%s\"\n", i, map->name);
>                 def = (struct bpf_map_def *)(data->d_buf + sym.st_value);
>                 /*
>                  * If the definition of the map in the object file fits in
> @@ -939,7 +969,7 @@ static int bpf_object__init_maps(struct bpf_object *obj, int flags)
>                  * calloc above.
>                  */
>                 if (map_def_sz <= sizeof(struct bpf_map_def)) {
> -                       memcpy(&obj->maps[map_idx].def, def, map_def_sz);
> +                       memcpy(&map->def, def, map_def_sz);
>                 } else {
>                         /*
>                          * Here the map structure being read is bigger than what
> @@ -959,37 +989,30 @@ static int bpf_object__init_maps(struct bpf_object *obj, int flags)
>                                                 return -EINVAL;
>                                 }
>                         }
> -                       memcpy(&obj->maps[map_idx].def, def,
> -                              sizeof(struct bpf_map_def));
> +                       memcpy(&map->def, def, sizeof(struct bpf_map_def));
>                 }
> -               map_idx++;
>         }
> +       return 0;
> +}
>
> -       if (!obj->caps.global_data)
> -               goto finalize;
> +static int bpf_object__init_maps(struct bpf_object *obj, int flags)
> +{
> +       bool strict = !(flags & MAPS_RELAX_COMPAT);
> +       int err;
>
> -       /*
> -        * Populate rest of obj->maps with libbpf internal maps.
> -        */
> -       if (obj->efile.data_shndx >= 0)
> -               ret = bpf_object__init_internal_map(obj, &obj->maps[map_idx++],
> -                                                   LIBBPF_MAP_DATA,
> -                                                   obj->efile.data,
> -                                                   &obj->sections.data);
> -       if (!ret && obj->efile.rodata_shndx >= 0)
> -               ret = bpf_object__init_internal_map(obj, &obj->maps[map_idx++],
> -                                                   LIBBPF_MAP_RODATA,
> -                                                   obj->efile.rodata,
> -                                                   &obj->sections.rodata);
> -       if (!ret && obj->efile.bss_shndx >= 0)
> -               ret = bpf_object__init_internal_map(obj, &obj->maps[map_idx++],
> -                                                   LIBBPF_MAP_BSS,
> -                                                   obj->efile.bss, NULL);
> -finalize:
> -       if (!ret)
> +       err = bpf_object__init_user_maps(obj, strict);
> +       if (err)
> +               return err;
> +
> +       err = bpf_object__init_global_data_maps(obj);
> +       if (err)
> +               return err;
> +
> +       if (obj->nr_maps) {
>                 qsort(obj->maps, obj->nr_maps, sizeof(obj->maps[0]),
>                       compare_bpf_map);
> -       return ret;
> +       }
> +       return 0;
>  }
>
>  static bool section_have_execinstr(struct bpf_object *obj, int idx)
> @@ -1262,14 +1285,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
>                 return -LIBBPF_ERRNO__FORMAT;
>         }
>         err = bpf_object__load_btf(obj, btf_data, btf_ext_data);
> -       if (err)
> -               return err;
> -       if (bpf_object__has_maps(obj)) {
> +       if (!err)
>                 err = bpf_object__init_maps(obj, flags);
> -               if (err)
> -                       return err;
> -       }
> -       err = bpf_object__init_prog_names(obj);
> +       if (!err)
> +               err = bpf_object__init_prog_names(obj);
>         return err;
>  }
>
> --
> 2.17.1
>