[PATCH] or1k: Avoid R_OR1K_GOT16 signed overflow by using special howto

[Giulio Benetti]

Hi Stafford, All,

On 02/01/22 01:03, Stafford Horne wrote:
> Previously when fixing PR 21464 we masked out upper bits of the
> relocation value in order to avoid overflow complaints when acceptable.
> It turns out this does not work when the relocation value ends up being
> signed.
> 
> To fix this this patch introduces a special howto with
> complain_on_overflow set to complain_overflow_dont.  This is used in
> place of the normal R_OR1K_GOT16 howto when we detect R_OR1K_GOT_AHI16
> relocations.
> 
> bfd/ChangeLog:
> 
> 	PR 28735
> 	* elf32-or1k.c (or1k_elf_got16_no_overflow_howto): Define.
> 	(or1k_elf_relocate_section): Use new howto instead of trying to
> 	mask out relocation bits.
> ---
>   bfd/elf32-or1k.c | 24 ++++++++++++++++++++----
>   1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/bfd/elf32-or1k.c b/bfd/elf32-or1k.c
> index 4f9092539f5..a2ff47473a7 100644
> --- a/bfd/elf32-or1k.c
> +++ b/bfd/elf32-or1k.c
> @@ -828,6 +828,23 @@ static reloc_howto_type or1k_elf_howto_table[] =
>   	 false),		/* pcrel_offset */
>   };
>   
> +/* A copy of the R_OR1K_GOT16 used in the presense of R_OR1K_GOT_AHI16
> +   relocations when we know we can ignore overflows.  */
> +static reloc_howto_type or1k_elf_got16_no_overflow_howto =
> +  HOWTO (R_OR1K_GOT16,		/* type */
> +	 0,			/* rightshift */
> +	 2,			/* size (0 = byte, 1 = short, 2 = long) */
> +	 16,			/* bitsize */
> +	 false,			/* pc_relative */
> +	 0,			/* bitpos */
> +	 complain_overflow_dont, /* complain_on_overflow */
> +	 bfd_elf_generic_reloc, /* special_function */
> +	 "R_OR1K_GOT16",	/* name */
> +	 false,			/* partial_inplace */
> +	 0,			/* src_mask */
> +	 0xffff,		/* dst_mask */
> +	 false);		/* pcrel_offset */
> +
>   /* Map BFD reloc types to Or1k ELF reloc types.  */
>   
>   struct or1k_reloc_map
> @@ -1506,12 +1523,11 @@ or1k_elf_relocate_section (bfd *output_bfd,
>   	    if (r_type == R_OR1K_GOT_AHI16)
>   	      saw_gotha = true;
>   
> -	    /* If we have a R_OR1K_GOT16 followed by a R_OR1K_GOT_AHI16
> +	    /* If we have a R_OR1K_GOT16 following a R_OR1K_GOT_AHI16
>   	       relocation we assume the code is doing the right thing to avoid
> -	       overflows.  Here we mask the lower 16-bit of the relocation to
> -	       avoid overflow validation failures.  */
> +	       overflows.  */
>   	    if (r_type == R_OR1K_GOT16 && saw_gotha)
> -	      relocation &= 0xffff;
> +	      howto = &or1k_elf_got16_no_overflow_howto;
>   
>   	  /* Addend should be zero.  */
>   	  if (rel->r_addend != 0)
> 

this patch fixes the problem.

Thanks a lot
Best regards
-- 
Giulio Benetti
Benetti Engineering sas