Re: [PATCH v4 14/22] objtool: Reuse string references

On Sat, Aug 8, 2026 at 4:18 PM Josh Poimboeuf <[email protected]> wrote:
>
> For duplicate strings, elf_add_string() just blindly adds duplicates.
>
> That can be a problem for arm64 which often uses two consecutive
> instructions (and corresponding relocations) to put an address into a
> register, like:
>
>   d8:   90000001        adrp    x1, 0 <meminfo_proc_show>       d8: R_AARCH64_ADR_PREL_PG_HI21  .rodata.meminfo_proc_show.str1.8
>   dc:   91000021        add     x1, x1, #0x0    dc: R_AARCH64_ADD_ABS_LO12_NC   .rodata.meminfo_proc_show.str1.8
>
> Referencing two different addresses in the ADRP+ADD pair would corrupt
> the memory access.  Avoid that by detecting and reusing duplicates when
> cloning string relocs.
>
> Signed-off-by: Josh Poimboeuf <[email protected]>

Acked-by: Song Liu <[email protected]>

With one nitpick below:

> ---
>  tools/objtool/elf.c                 | 29 +++++++++++++++++++++++------
>  tools/objtool/include/objtool/elf.h |  3 ++-
>  tools/objtool/klp-diff.c            |  4 +++-
>  3 files changed, 28 insertions(+), 8 deletions(-)
>
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index 8bf225d70d918..3bb04d6155a8b 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -1379,9 +1379,27 @@ struct elf *elf_create_file(GElf_Ehdr *ehdr, const char *name)
>         return elf;
>  }
>
> -unsigned int elf_add_string(struct elf *elf, struct section *strtab, const char *str)
> +int elf_find_string(struct elf *elf, struct section *strtab, const char *str)
>  {

elf_find_string() returns -1 for error and positive number for addend.
It is a good idea to add some comments for this behavior.

Thanks,
Song

[...]