Re: [Xen-devel] [PATCH LIVEPATCH-BUILD-TOOLS] create-diff-object: Update fixup offsets in .rela.ex_table

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 11/24/2016 01:08 AM, Konrad Rzeszutek Wilk wrote:
> From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
>
> When pruning entries from the fixup table, update the offsets in
> .rela.ex_table otherwise the relas might point to the wrong fixup entry
> or even out of the .fixup section.
>
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
> ---
> v2: Squashed fix from kpatch upstream
>    [see https://github.com/dynup/kpatch/pull/616]
> ---
>  create-diff-object.c | 41 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
>
> diff --git a/create-diff-object.c b/create-diff-object.c
> index 69bcd88..58f7c4c 100644
> --- a/create-diff-object.c
> +++ b/create-diff-object.c
> @@ -1057,6 +1057,34 @@ static int should_keep_rela_group(struct section *sec, 
> int start, int size)
>         return found;
>  }
>
> +/*
> + * When updating .fixup, the corresponding addends in .ex_table need to be
> + * updated too. Stash the result in rela.r_addend so that the calculation in
> + * fixup_group_size() is not affected.
> + */
> +void kpatch_update_ex_table_addend(struct kpatch_elf *kelf,
> +                                  struct special_section *special,
> +                                  int src_offset, int dest_offset,
> +                                  int group_size)
> +{
> +       struct rela *rela;
> +       struct section *sec;
> +
> +       if (strcmp(special->name, ".fixup"))
> +               return;
As suggested by kpatch upstream, the code would be clearer if the above 
check is in kpatch_regenerate_special_section() rather than this function.
I'll update and resend.

> +
> +       sec = find_section_by_name(&kelf->sections, ".rela.ex_table");
> +       if (!sec)
> +               ERROR("missing .rela.ex_table section");
> +
> +       list_for_each_entry(rela, &sec->relas, list) {
> +               if (!strcmp(rela->sym->name, ".fixup") &&
> +                   rela->addend >= src_offset &&
> +                   rela->addend < src_offset + group_size)
> +                       rela->rela.r_addend = rela->addend - (src_offset - 
> dest_offset);
> +       }
> +}
> +
>  static void kpatch_regenerate_special_section(struct kpatch_elf *kelf,
>                                               struct special_section *special,
>                                               struct section *sec)
> @@ -1073,6 +1101,14 @@ static void kpatch_regenerate_special_section(struct 
> kpatch_elf *kelf,
>         if (!dest)
>                 ERROR("malloc");
>
> +       /* Restore the stashed r_addend from kpatch_update_ex_table_addend. */
> +       if (!strcmp(special->name, ".ex_table")) {
> +               list_for_each_entry(rela, &sec->relas, list) {
> +                       if (!strcmp(rela->sym->name, ".fixup"))
> +                               rela->addend = rela->rela.r_addend;
> +               }
> +       }
> +
>         group_size = 0;
>         src_offset = 0;
>         dest_offset = 0;
> @@ -1100,6 +1136,11 @@ static void kpatch_regenerate_special_section(struct 
> kpatch_elf *kelf,
>                                 rela->rela.r_offset = rela->offset;
>
>                                 rela->sym->include = 1;
> +
> +                               kpatch_update_ex_table_addend(kelf, special,
> +                                                             src_offset,
> +                                                             dest_offset,
> +                                                             group_size);
>                         }
>                 }

--
Ross Lagerwall

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