From: Nick Desaulniers <ndesaulniers@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
Nathan Chancellor <nathan@kernel.org>,
Nicolas Schier <nicolas@fjasle.eu>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Ard Biesheuvel <ardb@kernel.org>,
Fangrui Song <maskray@google.com>
Subject: Re: [PATCH v6 03/20] modpost: detect section mismatch for R_ARM_MOVW_ABS_NC and R_ARM_MOVT_ABS
Date: Mon, 22 May 2023 11:03:13 -0700 [thread overview]
Message-ID: <CAKwvOdmxLrE8VksbsSGirfTqnuhEFT__FuCG53ri3V42UbH5aw@mail.gmail.com> (raw)
In-Reply-To: <20230521160426.1881124-4-masahiroy@kernel.org>
+ linux-arm-kernel
On Sun, May 21, 2023 at 9:05 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> ARM defconfig misses to detect some section mismatches.
>
> [test code]
>
> #include <linux/init.h>
>
> int __initdata foo;
> int get_foo(int x) { return foo; }
>
> It is apparently a bad reference, but modpost does not report anything
> for ARM defconfig (i.e. multi_v7_defconfig).
>
> The test code above produces the following relocations.
>
> Relocation section '.rel.text' at offset 0x200 contains 2 entries:
> Offset Info Type Sym.Value Sym. Name
> 00000000 0000062b R_ARM_MOVW_ABS_NC 00000000 .LANCHOR0
> 00000004 0000062c R_ARM_MOVT_ABS 00000000 .LANCHOR0
>
> Relocation section '.rel.ARM.exidx' at offset 0x210 contains 2 entries:
> Offset Info Type Sym.Value Sym. Name
> 00000000 0000022a R_ARM_PREL31 00000000 .text
> 00000000 00001000 R_ARM_NONE 00000000 __aeabi_unwind_cpp_pr0
>
> Currently, R_ARM_MOVW_ABS_NC and R_ARM_MOVT_ABS are just skipped.
>
> Add code to handle them. I checked arch/arm/kernel/module.c to learn
> how the offset is encoded in the instruction.
>
> The referenced symbol in relocation might be a local anchor.
> If is_valid_name() returns false, let's search for a better symbol name.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> scripts/mod/modpost.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 34fbbd85bfde..ed2301e951a9 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1108,7 +1108,7 @@ static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym)
> /**
> * Find symbol based on relocation record info.
> * In some cases the symbol supplied is a valid symbol so
> - * return refsym. If st_name != 0 we assume this is a valid symbol.
> + * return refsym. If is_valid_name() == true, we assume this is a valid symbol.
> * In other cases the symbol needs to be looked up in the symbol table
> * based on section and address.
> * **/
> @@ -1121,7 +1121,7 @@ static Elf_Sym *find_tosym(struct elf_info *elf, Elf64_Sword addr,
> Elf64_Sword d;
> unsigned int relsym_secindex;
>
> - if (relsym->st_name != 0)
> + if (is_valid_name(elf, relsym))
> return relsym;
>
> /*
> @@ -1312,11 +1312,19 @@ 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);
> Elf_Sym *sym = elf->symtab_start + ELF_R_SYM(r->r_info);
> unsigned int inst = TO_NATIVE(*reloc_location(elf, sechdr, r));
> + int offset;
>
> switch (r_typ) {
> case R_ARM_ABS32:
> r->r_addend = inst + sym->st_value;
> break;
> + case R_ARM_MOVW_ABS_NC:
> + case R_ARM_MOVT_ABS:
> + offset = ((inst & 0xf0000) >> 4) | (inst & 0xfff);
> + offset = (offset ^ 0x8000) - 0x8000;
The code in arch/arm/kernel/module.c then right shifts the offset by
16 for R_ARM_MOVT_ABS. Is that necessary?
> + offset += sym->st_value;
> + r->r_addend = offset;
> + break;
> case R_ARM_PC24:
> case R_ARM_CALL:
> case R_ARM_JUMP24:
> --
> 2.39.2
>
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2023-05-22 18:03 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-21 16:04 [PATCH v6 00/20] Unify <linux/export.h> and <asm/export.h>, remove EXPORT_DATA_SYMBOL(), faster TRIM_UNUSED_KSYMS Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 01/20] Revert "modpost: skip ELF local symbols during section mismatch check" Masahiro Yamada
2023-05-22 17:42 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 02/20] modpost: fix section mismatch message for R_ARM_ABS32 Masahiro Yamada
2023-05-22 17:56 ` Nick Desaulniers
2023-05-22 21:35 ` Ard Biesheuvel
2023-05-23 5:07 ` Masahiro Yamada
2023-05-23 7:13 ` Ard Biesheuvel
2023-05-21 16:04 ` [PATCH v6 03/20] modpost: detect section mismatch for R_ARM_MOVW_ABS_NC and R_ARM_MOVT_ABS Masahiro Yamada
2023-05-22 18:03 ` Nick Desaulniers [this message]
2023-05-22 21:50 ` Ard Biesheuvel
2023-05-23 11:58 ` Masahiro Yamada
2023-05-23 12:20 ` Ard Biesheuvel
2023-05-24 0:02 ` Masahiro Yamada
2023-05-24 0:04 ` Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 04/20] modpost: remove unused argument from secref_whitelist() Masahiro Yamada
2023-05-22 18:10 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 05/20] modpost: refactor find_fromsym() and find_tosym() Masahiro Yamada
2023-05-22 18:18 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 06/20] modpost: unify 'sym' and 'to' in default_mismatch_handler() Masahiro Yamada
2023-05-22 18:23 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 07/20] modpost: replace r->r_offset, r->r_addend with faddr, taddr Masahiro Yamada
2023-05-22 18:31 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 08/20] modpost: remove is_shndx_special() check from section_rel(a) Masahiro Yamada
2023-05-25 17:20 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 09/20] modpost: pass struct module pointer to check_section_mismatch() Masahiro Yamada
2023-05-25 17:23 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 10/20] kbuild: generate KSYMTAB entries by modpost Masahiro Yamada
2023-05-25 17:50 ` Nick Desaulniers
2023-06-02 13:51 ` Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 11/20] ia64,export.h: replace EXPORT_DATA_SYMBOL* with EXPORT_SYMBOL* Masahiro Yamada
2023-05-25 17:52 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 12/20] modpost: check static EXPORT_SYMBOL* by modpost again Masahiro Yamada
2023-05-25 18:18 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 13/20] modpost: squash sym_update_namespace() into sym_add_exported() Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 14/20] modpost: use null string instead of NULL pointer for default namespace Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 15/20] kbuild: implement CONFIG_TRIM_UNUSED_KSYMS without recursion Masahiro Yamada
2023-05-25 18:14 ` Nick Desaulniers
2023-05-28 7:40 ` Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 16/20] modpost: merge fromsec=DATA_SECTIONS entries in sectioncheck table Masahiro Yamada
2023-05-25 18:30 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 17/20] modpost: merge bad_tosec=ALL_EXIT_SECTIONS " Masahiro Yamada
2023-05-25 18:36 ` Nick Desaulniers
2023-05-28 16:43 ` Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 18/20] modpost: remove *_sections[] arrays Masahiro Yamada
2023-05-21 16:04 ` [PATCH v6 19/20] modpost: merge two similar section mismatch warnings Masahiro Yamada
2023-05-25 18:20 ` Nick Desaulniers
2023-05-21 16:04 ` [PATCH v6 20/20] modpost: show offset from symbol for " Masahiro Yamada
2023-05-25 18:26 ` Nick Desaulniers
2023-05-28 7:29 ` Masahiro Yamada
2023-05-22 1:47 ` [PATCH v6 00/20] Unify <linux/export.h> and <asm/export.h>, remove EXPORT_DATA_SYMBOL(), faster TRIM_UNUSED_KSYMS Masahiro Yamada
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