Re: [RFC] Use address_from_register in dwarf2-frame.c:read_addr_from_reg

[Andrew Pinski <pinskia@gmail.com>]

On Wed, Aug 27, 2014 at 5:21 AM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
> Andrew Pinski wrote:
>
>> I think this patch broke MIPS64 n32 big-endian support.  We assert here:
>> gdb_assert (!gdbarch_convert_register_p (gdbarch, regnum, type));
>>
>> The convert_register_p code for MIPS does:
>>   return (register_size (gdbarch, regnum) == 8
>>           && regnum % num_regs > 0 && regnum % num_regs < 32
>>           && TYPE_LENGTH (type) < 8);
>>
>>
>> Since the register size is 8 byte wide (MIPS64) and the type length is
>> 4 (pointer), we return true.  In MIPS64, the registers are stored
>> 64bits but pointers are 32bits.
>>
>> Here is the code that is used by mips_register_to_value:
>>       int len = TYPE_LENGTH (type);
>>       CORE_ADDR offset;
>>
>>       offset = gdbarch_byte_order (gdbarch) == BFD_ENDIAN_BIG ? 8 - len : 0;
>>       if (!get_frame_register_bytes (frame, regnum, offset, len, to,
>>     optimizedp, unavailablep))
>> return 0;
>>
>>       *optimizedp = *unavailablep = 0;
>>       return 1;
>
> Huh, I wasn't aware of that conversion.  Note that for the register_to_value
> case, I don't actually see any difference to the default behavior; it's the
> value_to_register routine that's really special (because of the sign-extension
> in performs).
>
>> Is there a way to fix this in a target neutral way?  (I might need a
>> way like this for AARCH64 ILP32 also).
>
> I guess it isn't too hard to support gdbarch_convert_register_p in that
> routine as well; I just didn't have any target to test on.
>
> Can you try whether something along the following lines works for you?

Yes this works for me.

Thanks,
Andrew Pinski


>
> Bye,
> Ulrich
>
> ChangeLog:
>
>         * findvar.c (address_from_register): Handle targets requiring
>         a special conversion routine even for plain pointer types.
>
> diff --git a/gdb/findvar.c b/gdb/findvar.c
> index 41887de..ba3dd4d 100644
> --- a/gdb/findvar.c
> +++ b/gdb/findvar.c
> @@ -764,11 +764,28 @@ address_from_register (int regnum, struct frame_info *frame)
>       would therefore abort in get_frame_id.  However, since we only need
>       a temporary value that is never used as lvalue, we actually do not
>       really need to set its VALUE_FRAME_ID.  Therefore, we re-implement
> -     the core of value_from_register, but use the null_frame_id.
> +     the core of value_from_register, but use the null_frame_id.  */
>
> -     This works only if we do not require a special conversion routine,
> -     which is true for plain pointer types for all current targets.  */
> -  gdb_assert (!gdbarch_convert_register_p (gdbarch, regnum, type));
> +  /* Some targets require a special conversion routine even for plain
> +     pointer types.  Avoid constructing a value object in those cases.  */
> +  if (gdbarch_convert_register_p (gdbarch, regnum, type))
> +    {
> +      gdb_byte *buf = alloca (TYPE_LENGTH (type));
> +      int optim, unavail, ok;
> +
> +      ok = gdbarch_register_to_value (gdbarch, frame, regnum, type,
> +                                     buf, &optim, &unavail);
> +      if (!ok)
> +       {
> +         /* This function is used while computing a location expression.
> +            Complain about the value being optimized out, rather than
> +            letting value_as_address complain about some random register
> +            the expression depends on not being saved.  */
> +         error_value_optimized_out ();
> +       }
> +
> +      return unpack_long (type, buf);
> +    }
>
>    value = gdbarch_value_from_register (gdbarch, type, regnum, null_frame_id);
>    read_frame_register_value (value, frame);
>
> --
>   Dr. Ulrich Weigand
>   GNU/Linux compilers and toolchain
>   Ulrich.Weigand@de.ibm.com
>