[PATCH v5] MIPS: Reject branch absolute relocs for PIC for linking

[PATCH v5] MIPS: Reject branch absolute relocs for PIC for linking

[YunQiang Su]

The asm code like:
	b	(8)
will emit absolute relocs like:
	R_MIPS_PC16	*ABS*

If they are included into PIC shared objects or PIE executables,
the branch target will be like 0x12340000, which will make the
programs crash.
---
 bfd/elfxx-mips.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
index 69dd71419ff..9542250dec4 100644
--- a/bfd/elfxx-mips.c
+++ b/bfd/elfxx-mips.c
@@ -9258,6 +9258,15 @@ _bfd_mips_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
 		   (h) ? h->root.root.string : "a local symbol");
 	      break;
 	    default:
+	      if (branch_reloc_p (r_type) && r_symndx == STN_UNDEF)
+		{
+		  howto = MIPS_ELF_RTYPE_TO_HOWTO (abfd, r_type, NEWABI_P (abfd));
+		  info->callbacks->einfo
+		    /* xgettext:c-format */
+		    (_("%X%H: relocation %s against `*ABS*' cannot be used"
+		       " when making a PIC/PIE object\n"),
+		     abfd, sec, rel->r_offset, howto->name);
+		}
 	      break;
 	    }
 	}
-- 
2.39.2

Re: [PATCH v5] MIPS: Reject branch absolute relocs for PIC for linking

[YunQiang Su]

YunQiang Su <syq@gcc.gnu.org> 于2024年2月8日周四 01:31写道：
>
> The asm code like:
>         b       (8)
> will emit absolute relocs like:
>         R_MIPS_PC16     *ABS*
>
> If they are included into PIC shared objects or PIE executables,
> the branch target will be like 0x12340000, which will make the
> programs crash.

@Maciej ping.

> ---
>  bfd/elfxx-mips.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
> index 69dd71419ff..9542250dec4 100644
> --- a/bfd/elfxx-mips.c
> +++ b/bfd/elfxx-mips.c
> @@ -9258,6 +9258,15 @@ _bfd_mips_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
>                    (h) ? h->root.root.string : "a local symbol");
>               break;
>             default:
> +             if (branch_reloc_p (r_type) && r_symndx == STN_UNDEF)
> +               {
> +                 howto = MIPS_ELF_RTYPE_TO_HOWTO (abfd, r_type, NEWABI_P (abfd));
> +                 info->callbacks->einfo
> +                   /* xgettext:c-format */
> +                   (_("%X%H: relocation %s against `*ABS*' cannot be used"
> +                      " when making a PIC/PIE object\n"),
> +                    abfd, sec, rel->r_offset, howto->name);
> +               }
>               break;
>             }
>         }
> --
> 2.39.2
>

Re: [PATCH v5] MIPS: Reject branch absolute relocs for PIC for linking

[Maciej W. Rozycki]

On Thu, 8 Feb 2024, YunQiang Su wrote:

> The asm code like:
> 	b	(8)
> will emit absolute relocs like:
> 	R_MIPS_PC16	*ABS*
> 
> If they are included into PIC shared objects or PIE executables,
> the branch target will be like 0x12340000, which will make the
> programs crash.

 This needs a proper LD test case.  I don't think `8' needs to be 
parenthesised here.

  Maciej