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

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

[Stafford Horne]

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)
-- 
2.31.1

Re: [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