Re: [PATCH] mips: pldd: support DT_MIPS_RLD_MAP and DT_MIPS_RLD_MAP_REL

[Carlos O'Donell <carlos@redhat.com>]

On 1/28/22 15:48, Adhemerval Zanella via Libc-alpha wrote:
> 
> 
> On 28/01/2022 17:45, H.J. Lu via Libc-alpha wrote:
>> 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.
>>
> 
> Agreed, I think we should avoid arch specific defines (__mips__) on generic
> code.
 
Ah! I see, the objection if about arch-defines in tests. Yes, lets clean that up.

-- 
Cheers,
Carlos.