Re: [Xen-devel] [PATCH v2] create-diff-object: Update fixup offsets in .rela.ex_table

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Dec 12, 2016 at 02:52:34PM +0000, Ross Lagerwall wrote:
> 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.
> 
> This is a port of kpatch's commit 13d61012f9b2 ("create-diff-object:
> Update fixup offsets in .rela__ex_table").
> 
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Thanks!
> ---
> 
> Changed in v2:
> * Updated to match the patch which went into kpatch.
> 
>  create-diff-object.c | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/create-diff-object.c b/create-diff-object.c
> index b0d1348..f07e727 100644
> --- a/create-diff-object.c
> +++ b/create-diff-object.c
> @@ -1057,6 +1057,31 @@ 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;
> +
> +     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 +1098,14 @@ 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 +1133,12 @@ static void kpatch_regenerate_special_section(struct 
> kpatch_elf *kelf,
>                               rela->rela.r_offset = rela->offset;
>  
>                               rela->sym->include = 1;
> +
> +                             if (!strcmp(special->name, ".fixup"))
> +                                     kpatch_update_ex_table_addend(kelf, 
> special,
> +                                                                   
> src_offset,
> +                                                                   
> dest_offset,
> +                                                                   
> group_size);
>                       }
>               }
>  
> -- 
> 2.7.4
> 

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