linux-kernel - Re: [PATCH] modpost: fix section mismatch message for RELA

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Message-ID: <CAKwvOd=TmAh-eAmOzRxb6Gri8AfOXc7t9mPXgDgDTtAnegZ3iw@mail.gmail.com>
Date:   Tue, 31 Oct 2023 11:07:22 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Albert Ou <aou@...s.berkeley.edu>,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org, Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH] modpost: fix section mismatch message for RELA

On Tue, Oct 31, 2023 at 10:46 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> The section mismatch check prints a bogus symbol name on some
> architectures.
>
> [test code]
>
>   #include <linux/init.h>
>
>   int __initdata foo;
>   int get_foo(void) { return foo; }
>
> If you compile it with GCC for riscv or loongarch, modpost will show an
> incorrect symbol name:
>
>   WARNING: modpost: vmlinux: section mismatch in reference: get_foo+0x8 (section: .text) -> done (section: .init.data)
>
> To get the correct symbol address, st_value must be added
>
> This issue has never been noticed since commit 93684d3b8062 ("kbuild:
> include symbol names in section mismatch warnings") presumably because
> st_value becomes zero on most architectures when the referenced symbol
> is looked up. It is not true for riscv or loongarch, at least.
>
> With this fix, modpost will show the correct symbol name:
>
>   WARNING: modpost: vmlinux: section mismatch in reference: get_foo+0x8 (section: .text) -> foo (section: .init.data)
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>
>  scripts/mod/modpost.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 973b5e5ae2dd..cb6406f485a9 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1383,13 +1383,15 @@ static void section_rela(struct module *mod, struct elf_info *elf,
>         const Elf_Rela *rela;
>
>         for (rela = start; rela < stop; rela++) {
> +               Elf_Sym *tsym;
>                 Elf_Addr taddr, r_offset;
>                 unsigned int r_type, r_sym;
>
>                 r_offset = TO_NATIVE(rela->r_offset);
>                 get_rel_type_and_sym(elf, rela->r_info, &r_type, &r_sym);
>
> -               taddr = TO_NATIVE(rela->r_addend);
> +               tsym = elf->symtab_start + r_sym;
> +               taddr = tsym->st_value + TO_NATIVE(rela->r_addend);
>
>                 switch (elf->hdr->e_machine) {
>                 case EM_RISCV:
> @@ -1404,7 +1406,7 @@ static void section_rela(struct module *mod, struct elf_info *elf,
>                         break;
>                 }
>
> -               check_section_mismatch(mod, elf, elf->symtab_start + r_sym,
> +               check_section_mismatch(mod, elf, tsym,
>                                        fsecndx, fromsec, r_offset, taddr);
>         }
>  }
> --
> 2.40.1
>


-- 
Thanks,
~Nick Desaulniers