[PATCH] mips: pldd: support DT_MIPS_RLD_MAP and DT_MIPS_RLD_MAP_REL

[H.J. Lu]

On Fri, Jan 28, 2022 at 10:57 AM Xi Ruoyao via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> MIPS uses DT_MIPS_RLD_MAP and DT_MIPS_RLD_MAP_REL for accessing r_debug,
> instead of DT_DEBUG.
> ---
>  elf/pldd-xx.c | 67 ++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 53 insertions(+), 14 deletions(-)
>
> diff --git a/elf/pldd-xx.c b/elf/pldd-xx.c
> index 1cdfb49c53..ec397f00e5 100644
> --- a/elf/pldd-xx.c
> +++ b/elf/pldd-xx.c
> @@ -22,6 +22,12 @@
>  #define EW_(e, w, t) EW__(e, w, _##t)
>  #define EW__(e, w, t) e##w##t
>
> +#if CLASS == 32
> +typedef Elf32_Word E(val_type);
> +#else
> +typedef Elf64_Xword E(val_type);
> +#endif
> +
>  struct E(link_map)
>  {
>    EW(Addr) l_addr;
> @@ -70,6 +76,35 @@ _Static_assert (offsetof (struct r_debug, r_map)
>                 == offsetof (struct E(r_debug), r_map), "r_map");
>  #endif
>
> +static EW(Addr)
> +E(r_debug_offset) (EW(Dyn) *d, int memfd, EW(Addr) d_addr)
> +{
> +#ifdef __mips__
> +  EW(Addr) ptr;
> +
> +  switch (d->d_tag)
> +    {
> +    case DT_MIPS_RLD_MAP_REL:
> +      ptr = d_addr + d->d_un.d_val;
> +      break;
> +    case DT_MIPS_RLD_MAP:
> +      ptr = d->d_un.d_ptr;
> +      break;
> +    default:
> +      return 0;
> +    }
> +
> +    if (pread (memfd, &ptr, sizeof (ptr), ptr) != sizeof (ptr))
> +      return 0;
> +
> +    return ptr;
> +#else
> +  if (d->d_tag == DT_DEBUG)
> +    return (off_t) d->d_un.d_ptr;
> +
> +  return 0;
> +#endif
> +}
>
>  static int
>
> @@ -126,21 +161,25 @@ E(find_maps) (const char *exe, int memfd, pid_t pid, void *auxv,
>             != p[i].p_filesz)
>           error (EXIT_FAILURE, 0, gettext ("cannot read dynamic section"));
>
> -       /* Search for the DT_DEBUG entry.  */
> +       /* Search for the r_debug struct.  */
>         for (unsigned int j = 0; j < p[i].p_filesz / sizeof (EW(Dyn)); ++j)
> -         if (dyn[j].d_tag == DT_DEBUG && dyn[j].d_un.d_ptr != 0)
> -           {
> -             struct E(r_debug) r;
> -             if (pread (memfd, &r, sizeof (r), dyn[j].d_un.d_ptr)
> -                 != sizeof (r))
> -               error (EXIT_FAILURE, 0, gettext ("cannot read r_debug"));
> -
> -             if (r.r_map != 0)
> -               {
> -                 list = r.r_map;
> -                 break;
> -               }
> -           }
> +         {
> +           EW(Addr) d_addr = offset + p[i].p_vaddr + sizeof (EW(Dyn)) * j;
> +           EW(Addr) off = E(r_debug_offset)(&dyn[j], memfd, d_addr);
> +           if (off != 0)
> +             {
> +               struct E(r_debug) r;
> +               if (pread (memfd, &r, sizeof (r), off)
> +                   != sizeof (r))
> +                 error (EXIT_FAILURE, 0, gettext ("cannot read r_debug"));
> +
> +               if (r.r_map != 0)
> +                 {
> +                   list = r.r_map;
> +                   break;
> +                 }
> +             }
> +         }
>
>         free (dyn);
>         break;
> --
> 2.35.0
>
>

I think a header file to access r_debug works better.  MIPS can provide
one to override the generic header file.

-- 
H.J.