+ linux-arm-kernel
On Sun, May 21, 2023 at 9:05 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
>
> 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
