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Message-ID: <CAK7LNARTN55RE18vXjMuAUO37kMeawBD4G=UcS6_j7U0asCZEA@mail.gmail.com>
Date: Tue, 26 Jul 2022 18:19:31 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Mauricio Faria de Oliveira <mfo@...onical.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-modules <linux-modules@...r.kernel.org>,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
Michal Marek <michal.lkml@...kovi.net>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Luis Chamberlain <mcgrof@...nel.org>,
Kees Cook <keescook@...omium.org>,
Iurii Zaikin <yzaikin@...gle.com>
Subject: Re: [RFC PATCH 2/6] modpost: deduplicate section_rel[a]()
On Fri, Jul 22, 2022 at 11:24 AM Mauricio Faria de Oliveira
<mfo@...onical.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@...onical.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
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