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

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, May 25, 2022 at 9:52 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * 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

Linker always sets r_addend to 0 for R_X86_64_GLOB_DAT and
R_X86_64_JUMP_SLOT.

> that this change introduces hard-to-diagnose regressions.
>
> Thanks,
> Florian
>


-- 
H.J.