[PATCH v6 2/5] elf: Properly handle zero DT_RELA/DT_REL values

[Adhemerval Zanella]

On 10/03/2022 17:03, H.J. Lu via Libc-alpha wrote:
> With DT_RELR, there may be no relocations in DT_RELA/DT_REL and their
> entry values are zero.  Don't relocate DT_RELA/DT_REL and update the
> combined relocation start address if their entry values are zero.

Patch looks good with the two small fixes below.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  elf/dynamic-link.h     |  6 +++++-
>  elf/get-dynamic-info.h | 18 ++++++++++++++----
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/elf/dynamic-link.h b/elf/dynamic-link.h
> index d04c457e55..252f407a12 100644
> --- a/elf/dynamic-link.h
> +++ b/elf/dynamic-link.h
> @@ -84,7 +84,9 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
>  	     __typeof (((ElfW(Dyn) *) 0)->d_un.d_val) nrelative; int lazy; }  \
>        ranges[2] = { { 0, 0, 0, 0 }, { 0, 0, 0, 0 } };			      \
>  									      \
> -    if ((map)->l_info[DT_##RELOC])					      \
> +    /* With DT_RELR, DT_RELA/DT_REL can have zero value.  */		      \
> +    if ((map)->l_info[DT_##RELOC]					      \

Compare to NULL here.

> +	&& (map)->l_info[DT_##RELOC]->d_un.d_ptr != 0)			      \
>        {									      \
>  	ranges[0].start = D_PTR ((map), l_info[DT_##RELOC]);		      \
>  	ranges[0].size = (map)->l_info[DT_##RELOC##SZ]->d_un.d_val;	      \
> @@ -98,6 +100,8 @@ elf_machine_lazy_rel (struct link_map *map, struct r_scope_elem *scope[],
>  	ElfW(Addr) start = D_PTR ((map), l_info[DT_JMPREL]);		      \
>  	ElfW(Addr) size = (map)->l_info[DT_PLTRELSZ]->d_un.d_val;	      \
>  									      \
> +	if (ranges[0].start == 0)					      \
> +	  ranges[0].start = start;					      \
>  	if (ranges[0].start + ranges[0].size == (start + size))		      \
>  	  ranges[0].size -= size;					      \
>  	if (!(do_lazy)							      \

Ok.

> diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
> index 6c2a3a12b1..f4b957684b 100644
> --- a/elf/get-dynamic-info.h
> +++ b/elf/get-dynamic-info.h
> @@ -83,16 +83,26 @@ elf_get_dynamic_info (struct link_map *l, bool bootstrap,
>        ADJUST_DYN_INFO (DT_PLTGOT);
>        ADJUST_DYN_INFO (DT_STRTAB);
>        ADJUST_DYN_INFO (DT_SYMTAB);
> +      ADJUST_DYN_INFO (DT_RELR);
> +      ADJUST_DYN_INFO (DT_JMPREL);
> +      ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
> +      ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
> +# undef ADJUST_DYN_INFO
> +
> +      /* DT_RELA/DT_REL are mandatory.  But they may have zero value if
> +	 there is DT_RELR.  Don't relocate them if they are zero.  */
> +# define ADJUST_DYN_INFO(tag) \
> +      do								      \
> +	if (info[tag] != NULL && info[tag]->d_un.d_ptr != 0)		      \
> +         info[tag]->d_un.d_ptr += l_addr;				      \
> +      while (0)
> +

Maybe use '{' and '}' on the do ... while.

>  # if ! ELF_MACHINE_NO_RELA
>        ADJUST_DYN_INFO (DT_RELA);
>  # endif
>  # if ! ELF_MACHINE_NO_REL
>        ADJUST_DYN_INFO (DT_REL);
>  # endif
> -      ADJUST_DYN_INFO (DT_RELR);
> -      ADJUST_DYN_INFO (DT_JMPREL);
> -      ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
> -      ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
>  # undef ADJUST_DYN_INFO
>      }
>    if (info[DT_PLTREL] != NULL)

Ok.