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Re: [RFC] Use address_from_register in dwarf2-frame.c:read_addr_from_reg
- From: Andrew Pinski <pinskia at gmail dot com>
- To: Ulrich Weigand <uweigand at de dot ibm dot com>
- Cc: "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>
- Date: Sat, 6 Sep 2014 15:34:45 -0700
- Subject: Re: [RFC] Use address_from_register in dwarf2-frame.c:read_addr_from_reg
- Authentication-results: sourceware.org; auth=none
- References: <CA+=Sn1=4+tFKYtZgAbUVk86bHPWbF3FT+9HZNG8zU18wEX08Tw at mail dot gmail dot com> <201408271221 dot s7RCL684028429 at d06av02 dot portsmouth dot uk dot ibm dot 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
>