Re: [PATCH v3 12/28] Add indirect_implicit_ptr to dwarf_location class

[Lancelot SIX <lsix@lancelotsix.com>]

Hi,

I have included very minor comments in the patch.

On Thu, Oct 14, 2021 at 10:32:19AM +0100, Zoran Zaric via Gdb-patches wrote:
> From: Zoran Zaric <Zoran.Zaric@amd.com>
> 
> Similarly to the is_implicit_ptr_at method, the existing function
> callback interface of the computed struct value, requiers a way to
> apply indirection to an implicit pointer on a given offset of a given
> length of an underlying location description.
> 
> This is different then reading from a struct value object (previously

then -> than

> described write_to_gdb_value method) in a way that the result of this
> operation is expected to be a struct value of a pointed source level
> variable instead of reading the value of that variable.
> 
> In the same way this is also different operation then the deref method

then -> than

> because the deref returns a read value of a given type from that
> location description.
> 
> gdb/ChangeLog:
> 
>         * dwarf2/expr.c (dwarf_location::indirect_implicit_ptr):
>         New method.
>         (dwarf_implicit_pointer::indirect_implicit_ptr): New method.
>         (dwarf_composite::indirect_implicit_ptr): New method.
> ---
>  gdb/dwarf2/expr.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 73 insertions(+)
> 
> diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
> index aa36a992e09..af84710b054 100644
> --- a/gdb/dwarf2/expr.c
> +++ b/gdb/dwarf2/expr.c
> @@ -474,6 +474,24 @@ class dwarf_location : public dwarf_entry
>       return false;
>    }
>  
> +  /* Recursive indirecting of the implicit pointer location description
> +     if that location is or encapsulates an implicit pointer.  The
> +     operation is performed in a given FRAME context, using the TYPE as
> +     the type of the pointer.  Where POINTER_OFFSET is an offset
> +     applied to that implicit pointer location description before the
> +     operation. BIT_OFFSET is a bit offset applied to the location and
                 ^^
Two spaces after the '.' here.

Best,
Lancelot.

> +     BIT_LENGTH is a bit length of the read.
> +
> +     Indirecting is only performed on the implicit pointer location
> +     description parts of the location.  */
> +  virtual value *indirect_implicit_ptr (frame_info *frame, struct type *type,
> +					LONGEST pointer_offset = 0,
> +					LONGEST bit_offset = 0,
> +					int bit_length = 0) const
> +  {
> +    return nullptr;
> +  }
> +
>  protected:
>    /* Architecture of the location.  */
>    gdbarch *m_arch;
> @@ -1103,6 +1121,11 @@ class dwarf_implicit_pointer final : public dwarf_location
>       return true;
>    }
>  
> +  value *indirect_implicit_ptr (frame_info *frame, struct type *type,
> +				LONGEST pointer_offset = 0,
> +				LONGEST bit_offset = 0,
> +				int bit_length = 0) const override;
> +
>  private:
>    /* Per object file data of the implicit pointer.  */
>    dwarf2_per_objfile *m_per_objfile;
> @@ -1155,6 +1178,17 @@ dwarf_implicit_pointer::read (frame_info *frame, gdb_byte *buf,
>      }
>  }
>  
> +value *
> +dwarf_implicit_pointer::indirect_implicit_ptr (frame_info *frame,
> +					       struct type *type,
> +					       LONGEST pointer_offset,
> +					       LONGEST bit_offset,
> +					       int bit_length) const
> +{
> +  return indirect_synthetic_pointer (m_die_offset, m_offset + pointer_offset,
> +				     m_per_cu, m_per_objfile, frame, type);
> +}
> +
>  /* Composite location description entry.  */
>  
>  class dwarf_composite final : public dwarf_location
> @@ -1191,6 +1225,11 @@ class dwarf_composite final : public dwarf_location
>  
>    bool is_implicit_ptr_at (LONGEST bit_offset, int bit_length) const override;
>  
> +  value *indirect_implicit_ptr (frame_info *frame, struct type *type,
> +				LONGEST pointer_offset = 0,
> +				LONGEST bit_offset = 0,
> +				int bit_length = 0) const override;
> +
>  private:
>    /* Composite piece that contains a piece location
>       description and it's size.  */
> @@ -1424,6 +1463,40 @@ dwarf_composite::is_implicit_ptr_at (LONGEST bit_offset, int bit_length) const
>      return false;
>  }
>  
> +value *
> +dwarf_composite::indirect_implicit_ptr (frame_info *frame, struct type *type,
> +					LONGEST pointer_offset,
> +					LONGEST bit_offset,
> +					int bit_length) const
> +{
> +  LONGEST total_bit_offset = HOST_CHAR_BIT * m_offset
> +			     + m_bit_suboffset + bit_offset;
> +
> +  /* Advance to the first non-skipped piece.  */
> +  for (const piece &piece : m_pieces)
> +    {
> +      ULONGEST read_bit_length = piece.size;
> +
> +      if (total_bit_offset >= read_bit_length)
> +	{
> +	  total_bit_offset -= read_bit_length;
> +	  continue;
> +	}
> +
> +      read_bit_length -= total_bit_offset;
> +
> +      if (bit_length < read_bit_length)
> +	read_bit_length = bit_length;
> +
> +      return piece.location->indirect_implicit_ptr (frame, type,
> +						    pointer_offset,
> +						    total_bit_offset,
> +						    read_bit_length);
> +    }
> +
> +  return nullptr;
> +}
> +
>  struct piece_closure
>  {
>    /* Reference count.  */
> -- 
> 2.17.1
>