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References: <20220722022416.137548-1-mfo@canonical.com> <20220722022416.137548-3-mfo@canonical.com>
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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Tue, 26 Jul 2022 18:19:31 +0900
Message-ID: <CAK7LNARTN55RE18vXjMuAUO37kMeawBD4G=UcS6_j7U0asCZEA@mail.gmail.com>
Subject: Re: [RFC PATCH 2/6] modpost: deduplicate section_rel[a]()
To:     Mauricio Faria de Oliveira <mfo@canonical.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-modules <linux-modules@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>
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On Fri, Jul 22, 2022 at 11:24 AM Mauricio Faria de Oliveira
<mfo@canonical.com> wrote:
>
> Now both functions are almost identical, and we can again generalize
> the relocation types Elf_Rela/Elf_Rel with Elf_Rela, and handle some
> differences with conditionals on section header type (SHT_RELA/REL).
>
> The important bit is to make sure the loop increment uses the right
> size for pointer arithmethic.
>
> The original reason for split functions to make program logic easier
> to follow; commit 5b24c0715fc4 ("kbuild: code refactoring in modpost").
>
> Hopefully these 2 commits may help improving that, without an impact
> in understanding the code due to generalization of relocation types.
>
> Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
> ---
>  scripts/mod/modpost.c | 61 ++++++++++++++++---------------------------
>  1 file changed, 23 insertions(+), 38 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 4c1038dccae0..d1ed67fa290b 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1794,63 +1794,49 @@ static int get_relx_sym(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *rela,
>         return 0;
>  }
>
> -static void section_rela(const char *modname, struct elf_info *elf,
> +/* The caller must ensure sechdr->sh_type == SHT_RELA or SHT_REL. */
> +static void section_relx(const char *modname, struct elf_info *elf,
>                          Elf_Shdr *sechdr)
>  {
>         Elf_Sym  *sym;
> -       Elf_Rela *rela;
> +       Elf_Rela *relx; /* access .r_addend in SHT_RELA _only_! */
>         Elf_Rela r;
> +       size_t relx_size;
>         const char *fromsec;
>
>         Elf_Rela *start = (void *)elf->hdr + sechdr->sh_offset;
>         Elf_Rela *stop  = (void *)start + sechdr->sh_size;
>
>         fromsec = sech_name(elf, sechdr);
> -       fromsec += strlen(".rela");
> +       if (sechdr->sh_type == SHT_RELA) {
> +               relx_size = sizeof(Elf_Rela);
> +               fromsec += strlen(".rela");
> +       } else if (sechdr->sh_type == SHT_REL) {
> +               relx_size = sizeof(Elf_Rel);
> +               fromsec += strlen(".rel");
> +       } else {
> +               error("%s: [%s.ko] not relocation section\n", fromsec, modname);


Nit.

modname already contains the suffix  ".o".

For vmlinux, the error message will print like this:
[vmlinux.o.ko]


> +               return;
> +       }
> +
>         /* if from section (name) is know good then skip it */
>         if (match(fromsec, section_white_list))
>                 return;
>
> -       for (rela = start; rela < stop; rela++) {
> -               if (get_relx_sym(elf, sechdr, rela, &r, &sym))
> +       for (relx = start; relx < stop; relx = (void *)relx + relx_size) {
> +               if (get_relx_sym(elf, sechdr, relx, &r, &sym))
>                         continue;
>
>                 switch (elf->hdr->e_machine) {
>                 case EM_RISCV:
> -                       if (!strcmp("__ex_table", fromsec) &&
> +                       if (sechdr->sh_type == SHT_RELA &&
> +                           !strcmp("__ex_table", fromsec) &&
>                             ELF_R_TYPE(r.r_info) == R_RISCV_SUB32)
>                                 continue;
>                         break;
>                 }
>
> -               if (is_second_extable_reloc(start, rela, fromsec))
> -                       find_extable_entry_size(fromsec, &r);
> -               check_section_mismatch(modname, elf, &r, sym, fromsec);
> -       }
> -}
> -
> -static void section_rel(const char *modname, struct elf_info *elf,
> -                       Elf_Shdr *sechdr)
> -{
> -       Elf_Sym *sym;
> -       Elf_Rel *rel;
> -       Elf_Rela r;
> -       const char *fromsec;
> -
> -       Elf_Rel *start = (void *)elf->hdr + sechdr->sh_offset;
> -       Elf_Rel *stop  = (void *)start + sechdr->sh_size;
> -
> -       fromsec = sech_name(elf, sechdr);
> -       fromsec += strlen(".rel");
> -       /* if from section (name) is know good then skip it */
> -       if (match(fromsec, section_white_list))
> -               return;
> -
> -       for (rel = start; rel < stop; rel++) {
> -               if (get_relx_sym(elf, sechdr, (Elf_Rela *)rel, &r, &sym)
> -                       continue;
> -
> -               if (is_second_extable_reloc(start, rel, fromsec))
> +               if (is_second_extable_reloc(start, relx, fromsec))
>                         find_extable_entry_size(fromsec, &r);
>                 check_section_mismatch(modname, elf, &r, sym, fromsec);
>         }
> @@ -1877,10 +1863,9 @@ static void check_sec_ref(const char *modname, struct elf_info *elf)
>         for (i = 0; i < elf->num_sections; i++) {
>                 check_section(modname, elf, &elf->sechdrs[i]);
>                 /* We want to process only relocation sections and not .init */
> -               if (sechdrs[i].sh_type == SHT_RELA)
> -                       section_rela(modname, elf, &elf->sechdrs[i]);
> -               else if (sechdrs[i].sh_type == SHT_REL)
> -                       section_rel(modname, elf, &elf->sechdrs[i]);
> +               if (sechdrs[i].sh_type == SHT_RELA ||
> +                   sechdrs[i].sh_type == SHT_REL)
> +                       section_relx(modname, elf, &elf->sechdrs[i]);
>         }
>  }
>
> --
> 2.25.1
>


-- 
Best Regards
Masahiro Yamada