linux-kernel - Re: [PATCH v5 14/21] modpost: remove is_shndx_special() check from section

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Message-ID: <CAK7LNARcSSA429nZENksFwVWu--gLhzymi06XLY7VpRimiHZaQ@mail.gmail.com>
Date:   Sat, 20 May 2023 22:45:48 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Pitre <npitre@...libre.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH v5 14/21] modpost: remove is_shndx_special() check from section_rel(a)

On Thu, May 18, 2023 at 6:23 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Sun, May 14, 2023 at 8:28 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > This check is unneeded. Without it, sec_name() will returns the null
> > string "", then section_mismatch() will return immediately.
> >
> > Anyway, special section indices do not appear quite often in these
> > loops.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
>
> Could almost eliminate is_shndx_special after this. I think there's
> only one callsite after this?

There will be no callsite of is_shndx_special().
I will remove the definition as well.



 (I should check with the series applied;
> this patch fails to apply on mainline if that's relevant for potential
> merge conflicts).
>
> Does doing that additional work speed things up though?


I do not know.

As I wrote in the comment, special indices rarely appear in
the relocation.
I do not believe "let's bail out earlier" does not buy us.



>
> > ---
> >
> >  scripts/mod/modpost.c | 16 ++++------------
> >  1 file changed, 4 insertions(+), 12 deletions(-)
> >
> > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > index 0ef9d6964b6a..28db215ecc71 100644
> > --- a/scripts/mod/modpost.c
> > +++ b/scripts/mod/modpost.c
> > @@ -1370,7 +1370,6 @@ static int addend_mips_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
> >  static void section_rela(const char *modname, struct elf_info *elf,
> >                          Elf_Shdr *sechdr)
> >  {
> > -       Elf_Sym  *sym;
> >         Elf_Rela *rela;
> >         Elf_Rela r;
> >         unsigned int r_sym;
> > @@ -1413,11 +1412,8 @@ static void section_rela(const char *modname, struct elf_info *elf,
> >                                 continue;
> >                         break;
> >                 }
> > -               sym = elf->symtab_start + r_sym;
> > -               /* Skip special sections */
> > -               if (is_shndx_special(sym->st_shndx))
> > -                       continue;
> > -               check_section_mismatch(modname, elf, sym,
> > +
> > +               check_section_mismatch(modname, elf, elf->symtab_start + r_sym,
> >                                        fsecndx, fromsec, r.r_offset, r.r_addend);
> >         }
> >  }
> > @@ -1425,7 +1421,6 @@ static void section_rela(const char *modname, struct elf_info *elf,
> >  static void section_rel(const char *modname, struct elf_info *elf,
> >                         Elf_Shdr *sechdr)
> >  {
> > -       Elf_Sym *sym;
> >         Elf_Rel *rel;
> >         Elf_Rela r;
> >         unsigned int r_sym;
> > @@ -1472,11 +1467,8 @@ static void section_rel(const char *modname, struct elf_info *elf,
> >                 default:
> >                         fatal("Please add code to calculate addend for this architecture\n");
> >                 }
> > -               sym = elf->symtab_start + r_sym;
> > -               /* Skip special sections */
> > -               if (is_shndx_special(sym->st_shndx))
> > -                       continue;
> > -               check_section_mismatch(modname, elf, sym,
> > +
> > +               check_section_mismatch(modname, elf, elf->symtab_start + r_sym,
> >                                        fsecndx, fromsec, r.r_offset, r.r_addend);
> >         }
> >  }
> > --
> > 2.39.2
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Best Regards
Masahiro Yamada