Re: [PATCH 1/2] btf_encoder: Move find_all_percpu_vars in generic collect_symbols

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This looks good to me. Thanks, Jiri.

Acked-by: Hao Luo <haoluo@xxxxxxxxxx>

On Sat, Oct 31, 2020 at 3:31 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> Moving find_all_percpu_vars under generic collect_symbols
> function that walks over symbols and calls collect_percpu_var.
>
> We will add another collect function that needs to go through
> all the symbols, so it's better we go through them just once.
>
> There's no functional change intended.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  btf_encoder.c | 124 +++++++++++++++++++++++++++-----------------------
>  1 file changed, 67 insertions(+), 57 deletions(-)
>
> diff --git a/btf_encoder.c b/btf_encoder.c
> index 4c92908beab2..1866bb16a8ba 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -250,75 +250,85 @@ static bool percpu_var_exists(uint64_t addr, uint32_t *sz, const char **name)
>         return true;
>  }
>
> -static int find_all_percpu_vars(struct btf_elf *btfe)
> +static int collect_percpu_var(struct btf_elf *btfe, GElf_Sym *sym)
>  {
> -       uint32_t core_id;
> -       GElf_Sym sym;
> +       const char *sym_name;
> +       uint64_t addr;
> +       uint32_t size;
>
> -       /* cache variables' addresses, preparing for searching in symtab. */
> -       percpu_var_cnt = 0;
> +       /* compare a symbol's shndx to determine if it's a percpu variable */
> +       if (elf_sym__section(sym) != btfe->percpu_shndx)
> +               return 0;
> +       if (elf_sym__type(sym) != STT_OBJECT)
> +               return 0;
>
> -       /* search within symtab for percpu variables */
> -       elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) {
> -               const char *sym_name;
> -               uint64_t addr;
> -               uint32_t size;
> +       addr = elf_sym__value(sym);
> +       /*
> +        * Store only those symbols that have allocated space in the percpu section.
> +        * This excludes the following three types of symbols:
> +        *
> +        *  1. __ADDRESSABLE(sym), which are forcely emitted as symbols.
> +        *  2. __UNIQUE_ID(prefix), which are introduced to generate unique ids.
> +        *  3. __exitcall(fn), functions which are labeled as exit calls.
> +        *
> +        * In addition, the variables defined using DEFINE_PERCPU_FIRST are
> +        * also not included, which currently includes:
> +        *
> +        *  1. fixed_percpu_data
> +        */
> +       if (!addr)
> +               return 0;
>
> -               /* compare a symbol's shndx to determine if it's a percpu variable */
> -               if (elf_sym__section(&sym) != btfe->percpu_shndx)
> -                       continue;
> -               if (elf_sym__type(&sym) != STT_OBJECT)
> -                       continue;
> +       size = elf_sym__size(sym);
> +       if (!size)
> +               return 0; /* ignore zero-sized symbols */
>
> -               addr = elf_sym__value(&sym);
> -               /*
> -                * Store only those symbols that have allocated space in the percpu section.
> -                * This excludes the following three types of symbols:
> -                *
> -                *  1. __ADDRESSABLE(sym), which are forcely emitted as symbols.
> -                *  2. __UNIQUE_ID(prefix), which are introduced to generate unique ids.
> -                *  3. __exitcall(fn), functions which are labeled as exit calls.
> -                *
> -                * In addition, the variables defined using DEFINE_PERCPU_FIRST are
> -                * also not included, which currently includes:
> -                *
> -                *  1. fixed_percpu_data
> -                */
> -               if (!addr)
> -                       continue;
> +       sym_name = elf_sym__name(sym, btfe->symtab);
> +       if (!btf_name_valid(sym_name)) {
> +               dump_invalid_symbol("Found symbol of invalid name when encoding btf",
> +                                   sym_name, btf_elf__verbose, btf_elf__force);
> +               if (btf_elf__force)
> +                       return 0;
> +               return -1;
> +       }
>
> -               size = elf_sym__size(&sym);
> -               if (!size)
> -                       continue; /* ignore zero-sized symbols */
> +       if (btf_elf__verbose)
> +               printf("Found per-CPU symbol '%s' at address 0x%lx\n", sym_name, addr);
>
> -               sym_name = elf_sym__name(&sym, btfe->symtab);
> -               if (!btf_name_valid(sym_name)) {
> -                       dump_invalid_symbol("Found symbol of invalid name when encoding btf",
> -                                           sym_name, btf_elf__verbose, btf_elf__force);
> -                       if (btf_elf__force)
> -                               continue;
> -                       return -1;
> -               }
> +       if (percpu_var_cnt == MAX_PERCPU_VAR_CNT) {
> +               fprintf(stderr, "Reached the limit of per-CPU variables: %d\n",
> +                       MAX_PERCPU_VAR_CNT);
> +               return -1;
> +       }
> +       percpu_vars[percpu_var_cnt].addr = addr;
> +       percpu_vars[percpu_var_cnt].sz = size;
> +       percpu_vars[percpu_var_cnt].name = sym_name;
> +       percpu_var_cnt++;
>
> -               if (btf_elf__verbose)
> -                       printf("Found per-CPU symbol '%s' at address 0x%lx\n", sym_name, addr);
> +       return 0;
> +}
> +
> +static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
> +{
> +       uint32_t core_id;
> +       GElf_Sym sym;
>
> -               if (percpu_var_cnt == MAX_PERCPU_VAR_CNT) {
> -                       fprintf(stderr, "Reached the limit of per-CPU variables: %d\n",
> -                               MAX_PERCPU_VAR_CNT);
> +       /* cache variables' addresses, preparing for searching in symtab. */
> +       percpu_var_cnt = 0;
> +
> +       /* search within symtab for percpu variables */
> +       elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) {
> +               if (collect_percpu_vars && collect_percpu_var(btfe, &sym))
>                         return -1;
> -               }
> -               percpu_vars[percpu_var_cnt].addr = addr;
> -               percpu_vars[percpu_var_cnt].sz = size;
> -               percpu_vars[percpu_var_cnt].name = sym_name;
> -               percpu_var_cnt++;
>         }
>
> -       if (percpu_var_cnt)
> -               qsort(percpu_vars, percpu_var_cnt, sizeof(percpu_vars[0]), percpu_var_cmp);
> +       if (collect_percpu_vars) {
> +               if (percpu_var_cnt)
> +                       qsort(percpu_vars, percpu_var_cnt, sizeof(percpu_vars[0]), percpu_var_cmp);
>
> -       if (btf_elf__verbose)
> -               printf("Found %d per-CPU variables!\n", percpu_var_cnt);
> +               if (btf_elf__verbose)
> +                       printf("Found %d per-CPU variables!\n", percpu_var_cnt);
> +       }
>         return 0;
>  }
>
> @@ -347,7 +357,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
>                 if (!btfe)
>                         return -1;
>
> -               if (!skip_encoding_vars && find_all_percpu_vars(btfe))
> +               if (collect_symbols(btfe, !skip_encoding_vars))
>                         goto out;
>
>                 has_index_type = false;
> --
> 2.26.2
>



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