Re: [PATCH v5 09/21] modpost: pass section index to find_elf_symbol2()

[Nick Desaulniers]

On Sun, May 14, 2023 at 8:28 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
>
> find_elf_symbol2() converts the section index to the section name,
> then compares the two section names in each iteration. This is slow.
>
> It is faster to compare the section indices (i.e. integers) directly.

Good idea!
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
>
>  scripts/mod/modpost.c | 34 +++++++++++++++-------------------
>  1 file changed, 15 insertions(+), 19 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 2cc9c2a4aadc..3b7b78e69137 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1169,19 +1169,14 @@ static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf64_Sword addr,
>   * it is, but this works for now.
>   **/
>  static Elf_Sym *find_elf_symbol2(struct elf_info *elf, Elf_Addr addr,
> -                                const char *sec)
> +                                unsigned int secndx)
>  {
>         Elf_Sym *sym;
>         Elf_Sym *near = NULL;
>         Elf_Addr distance = ~0;
>
>         for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
> -               const char *symsec;
> -
> -               if (is_shndx_special(sym->st_shndx))
> -                       continue;
> -               symsec = sec_name(elf, get_secindex(elf, sym));
> -               if (strcmp(symsec, sec) != 0)
> +               if (get_secindex(elf, sym) != secndx)
>                         continue;
>                 if (!is_valid_name(elf, sym))
>                         continue;
> @@ -1203,7 +1198,8 @@ static bool is_executable_section(struct elf_info *elf, unsigned int secndx)
>
>  static void default_mismatch_handler(const char *modname, struct elf_info *elf,
>                                      const struct sectioncheck* const mismatch,
> -                                    Elf_Rela *r, Elf_Sym *sym, const char *fromsec,
> +                                    Elf_Rela *r, Elf_Sym *sym,
> +                                    unsigned int fsecndx, const char *fromsec,
>                                      const char *tosec)
>  {
>         Elf_Sym *to;
> @@ -1211,7 +1207,7 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
>         const char *tosym;
>         const char *fromsym;
>
> -       from = find_elf_symbol2(elf, r->r_offset, fromsec);
> +       from = find_elf_symbol2(elf, r->r_offset, fsecndx);
>         fromsym = sym_name(elf, from);
>
>         to = find_elf_symbol(elf, r->r_addend, sym);
> @@ -1267,7 +1263,8 @@ static void default_mismatch_handler(const char *modname, struct elf_info *elf,
>  }
>
>  static void check_section_mismatch(const char *modname, struct elf_info *elf,
> -                                  Elf_Rela *r, Elf_Sym *sym, const char *fromsec)
> +                                  Elf_Rela *r, Elf_Sym *sym,
> +                                  unsigned int fsecndx, const char *fromsec)
>  {
>         const char *tosec = sec_name(elf, get_secindex(elf, sym));
>         const struct sectioncheck *mismatch = section_mismatch(fromsec, tosec);
> @@ -1275,7 +1272,8 @@ static void check_section_mismatch(const char *modname, struct elf_info *elf,
>         if (!mismatch)
>                 return;
>
> -       default_mismatch_handler(modname, elf, mismatch, r, sym, fromsec, tosec);
> +       default_mismatch_handler(modname, elf, mismatch, r, sym, fsecndx, fromsec,
> +                                tosec);
>  }
>
>  static unsigned int *reloc_location(struct elf_info *elf,
> @@ -1390,12 +1388,11 @@ static void section_rela(const char *modname, struct elf_info *elf,
>         Elf_Rela *rela;
>         Elf_Rela r;
>         unsigned int r_sym;
> -       const char *fromsec;
> -
> +       unsigned int fsecndx = sechdr->sh_info;
> +       const char *fromsec = sec_name(elf, fsecndx);
>         Elf_Rela *start = (void *)elf->hdr + sechdr->sh_offset;
>         Elf_Rela *stop  = (void *)start + sechdr->sh_size;
>
> -       fromsec = sec_name(elf, sechdr->sh_info);
>         /* if from section (name) is know good then skip it */
>         if (match(fromsec, section_white_list))
>                 return;
> @@ -1434,7 +1431,7 @@ static void section_rela(const char *modname, struct elf_info *elf,
>                 /* Skip special sections */
>                 if (is_shndx_special(sym->st_shndx))
>                         continue;
> -               check_section_mismatch(modname, elf, &r, sym, fromsec);
> +               check_section_mismatch(modname, elf, &r, sym, fsecndx, fromsec);
>         }
>  }
>
> @@ -1445,12 +1442,11 @@ static void section_rel(const char *modname, struct elf_info *elf,
>         Elf_Rel *rel;
>         Elf_Rela r;
>         unsigned int r_sym;
> -       const char *fromsec;
> -
> +       unsigned int fsecndx = sechdr->sh_info;
> +       const char *fromsec = sec_name(elf, fsecndx);
>         Elf_Rel *start = (void *)elf->hdr + sechdr->sh_offset;
>         Elf_Rel *stop  = (void *)start + sechdr->sh_size;
>
> -       fromsec = sec_name(elf, sechdr->sh_info);
>         /* if from section (name) is know good then skip it */
>         if (match(fromsec, section_white_list))
>                 return;
> @@ -1493,7 +1489,7 @@ static void section_rel(const char *modname, struct elf_info *elf,
>                 /* Skip special sections */
>                 if (is_shndx_special(sym->st_shndx))
>                         continue;
> -               check_section_mismatch(modname, elf, &r, sym, fromsec);
> +               check_section_mismatch(modname, elf, &r, sym, fsecndx, fromsec);
>         }
>  }
>
> --
> 2.39.2
>


-- 
Thanks,
~Nick Desaulniers