[PATCH] mips: pldd: support DT_MIPS_RLD_MAP and DT_MIPS_RLD_MAP_REL

[Adhemerval Zanella]

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.