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List:       linux-kbuild
Subject:    Re: [PATCH] modpost: fix section mismatch message for RELA
From:       Nick Desaulniers <ndesaulniers () google ! com>
Date:       2023-10-31 18:07:22
Message-ID: CAKwvOd=TmAh-eAmOzRxb6Gri8AfOXc7t9mPXgDgDTtAnegZ3iw () mail ! gmail ! com
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On Tue, Oct 31, 2023 at 10:46 AM Masahiro Yamada <masahiroy@kernel.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@kernel.org>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.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


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