[ was: Re: [PATCH 1/3] Add support for DW_OP_GNU_variable_value ]

On 08/23/2018 11:12 PM, Kevin Buettner wrote:
> On Wed, 22 Aug 2018 17:35:23 +0200
> Tom de Vries <tdevries@suse.de> wrote:
> 
>> On 08/18/2018 10:31 PM, Kevin Buettner wrote:
>>>     This patch adds support for DW_OP_GNU_variable_value to GDB.
>>>     
>>>     Jakub Jelinek provides a fairly expansive discussion of this DWARF
>>>     expression opcode in his GCC patch...
>>>     
>>>         https://gcc.gnu.org/ml/gcc-patches/2017-02/msg01499.html
>>>     
>>>     It has also been proposed for addition to the DWARF Standard:
>>>     
>>>         http://www.dwarfstd.org/ShowIssue.php?issue=161109.2  
>>
>> Hi,
>>
>> AFAIU from the discussion here (
>> https://gcc.gnu.org/ml/gcc-patches/2018-08/msg01351.html ) if:
>> - a DW_OP_GNU_variable_value refers to a die 'a', and
>> - there's a die 'b' with abstract_origin 'a' that does have a
>>   DW_AT_location, and
>> - die 'b' is 'in scope' in an evaluation context,
>> then the evaluation of DW_OP_GNU_variable_value 'a' should return the
>> value found at the DW_AT_location of die 'b'.
>>
>> I've written a gcc demonstrator patch to generate code like this for
>> VLAs, and found that gdb master (containing this patch series) does not
>> support this.
>>
>> Is this further support of DW_OP_GNU_variable_value something you're
>> currently working on, or plan to work on?
> 
> Tom and I discussed this briefly on IRC.  Tom says that he'll take
> a look at it...
> 

Hi,

sofar I've written:
- a hack that fixes the test-case I have, without regressing anything,
  and
- the rationale for the change,
hoping that this should sufficiently explain what we're trying to implement.

Hints on how to implement are welcome.

Thanks,
- Tom