Re: [PATCH] x86-64: Ignore r_addend for R_X86_64_GLOB_DAT/R_X86_64_JUMP_SLOT

[Florian Weimer <fweimer@redhat.com>]

* H. J. Lu via Libc-alpha:

> According to x86-64 psABI, r_addend should be ignored for R_X86_64_GLOB_DAT
> and R_X86_64_JUMP_SLOT.
> ---
>  sysdeps/x86_64/dl-machine.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
> index c70af7ab1e..7f607f6dff 100644
> --- a/sysdeps/x86_64/dl-machine.h
> +++ b/sysdeps/x86_64/dl-machine.h
> @@ -325,11 +325,13 @@ and creates an unsatisfiable circular dependency.\n",
>  #  endif
>  	  /* Set to symbol size plus addend.  */
>  	  value = sym->st_size;
> +	  *reloc_addr = value + reloc->r_addend;
> +	  break;
>  # endif
> -	  /* Fall through.  */
> +
>  	case R_X86_64_GLOB_DAT:
>  	case R_X86_64_JUMP_SLOT:
> -	  *reloc_addr = value + reloc->r_addend;
> +	  *reloc_addr = value;
>  	  break;
>  
>  	case R_X86_64_DTPMOD64:

Context:

	{
# ifndef RTLD_BOOTSTRAP
#  ifdef __ILP32__
	case R_X86_64_SIZE64:
	  /* Set to symbol size plus addend.  */
	  *(Elf64_Addr *) (uintptr_t) reloc_addr
	    = (Elf64_Addr) sym->st_size + reloc->r_addend;
	  break;

	case R_X86_64_SIZE32:
#  else
	case R_X86_64_SIZE64:
#  endif
	  /* Set to symbol size plus addend.  */
	  value = sym->st_size;
# endif
	  /* Fall through.  */
	case R_X86_64_GLOB_DAT:
	case R_X86_64_JUMP_SLOT:
	  *reloc_addr = value + reloc->r_addend;
	  break;


The new version is:

	{
# ifndef RTLD_BOOTSTRAP
#  ifdef __ILP32__
	case R_X86_64_SIZE64:
	  /* Set to symbol size plus addend.  */
	  *(Elf64_Addr *) (uintptr_t) reloc_addr
	    = (Elf64_Addr) sym->st_size + reloc->r_addend;
	  break;

	case R_X86_64_SIZE32:
#  else
	case R_X86_64_SIZE64:
#  endif
	  /* Set to symbol size plus addend.  */
	  value = sym->st_size;
	  *reloc_addr = value + reloc->r_addend;
	  break;
# endif
	case R_X86_64_GLOB_DAT:
	case R_X86_64_JUMP_SLOT:
	  *reloc_addr = value;
	  break;

So that “break” is actually in the right place.

Are there binaries out there with a non-zero addend?  I'm a bit worried
that this change introduces hard-to-diagnose regressions.

Thanks,
Florian