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

Tom de Vries
2018-08-22T15:35:21Z

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?

Thanks,
- Tom