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

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Message-ID: <CAKwvOdkMYKhm1gaDGxqa=J136J1=+vSv=fEVYNJR430Px5Qy6A@mail.gmail.com>
Date:   Wed, 17 May 2023 14:41:17 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH] modpost: fix section mismatch message for R_ARM_ABS32

On Sun, May 14, 2023 at 5:54 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> The section mismatch check does not show proper warning messages for ARM.
>
> Here, very simple test code.
>
>     #include <linux/init.h>
>
>     static int __initdata foo;
>
>     void set_foo(int x)
>     {
>             foo = x;
>     }
>
>     int get_foo(int x)
>     {
>             return foo;
>     }
>
> If I compile it for ARM, modpost does not show the symbol name.
>
>   WARNING: modpost: vmlinux.o: section mismatch in reference: set_foo (section: .text) -> (unknown) (section: .init.data)
>   WARNING: modpost: vmlinux.o: section mismatch in reference: get_foo (section: .text) -> (unknown) (section: .init.data)
>
> If I compile it for other architectures, modpost shows the correct symbol name.
>
>   WARNING: modpost: vmlinux.o: section mismatch in reference: set_foo (section: .text) -> foo (section: .init.data)
>   WARNING: modpost: vmlinux.o: section mismatch in reference: get_foo (section: .text) -> foo (section: .init.data)
>
> For R_ARM_ABS32, addend_arm_rel() sets r->r_addend to a wrong value.
>
> arch/arm/kernel/module.c handles R_ARM_ABS32 as follows:
>
>         case R_ARM_ABS32:
>         case R_ARM_TARGET1:
>                 *(u32 *)loc += sym->st_value;
>
> I just mimicked it in modpost.
>
> Fixes: 56a974fa2d59 ("kbuild: make better section mismatch reports on arm")
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  scripts/mod/modpost.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index d4531d09984d..c93780d93caf 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1460,12 +1460,13 @@ static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
>  static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
>  {
>         unsigned int r_typ = ELF_R_TYPE(r->r_info);
> +       unsigned int *location = reloc_location(elf, sechdr, r);

If `location` is only used in one case of the switch, consider
computing `location` only in that case.

> +       Elf_Sym *sym;
>
>         switch (r_typ) {
>         case R_ARM_ABS32:
> -               /* From ARM ABI: (S + A) | T */
> -               r->r_addend = (int)(long)
> -                             (elf->symtab_start + ELF_R_SYM(r->r_info));
> +               sym = elf->symtab_start + ELF_R_SYM(r->r_info);
> +               r->r_addend = TO_NATIVE(*location) + sym->st_value;
>                 break;
>         case R_ARM_PC24:
>         case R_ARM_CALL:
> --
> 2.39.2
>


-- 
Thanks,
~Nick Desaulniers