On Tue, Mar 05, 2019 at 04:06:59PM -0500, Jason Merrill wrote:
> > Assuming output_view_list_offset is correct, the following patch adjusts
> > size_of_die/value_format accordingly.
>
> I would guess that omitting the handling from output_view_list_offset was an
> oversight in the view work. Alex, which is right? :)
I had further look today. Alex has added multiple modes, with
-gvariable-location-views=incompat5 the location view stuff is emitted
directly into the .debug_loclist section as part of the sequence, like:
.uleb128 0 # DW_AT_location (*.LLST0)
...
.section .debug_loclists.dwo,"e",@progbits
.long .Ldebug_loc3-.Ldebug_loc2 # Length of Location Lists
.Ldebug_loc2:
.value 0x5 # DWARF version number
.byte 0x8 # Address Size
.byte 0 # Segment Size
.long 0x3 # Offset Entry Count
.Ldebug_loc0:
.long .LLST0-.Ldebug_loc0
.long .LLST1-.Ldebug_loc0
.long .LLST2-.Ldebug_loc0
.LLST0:
.byte 0x9 # DW_LLE_view_pair
.uleb128 0 # Location view begin
.uleb128 .LVU6 # Location view end
.byte 0x3 # DW_LLE_startx_length (*.LLST0)
.uleb128 0x2 # Location list range start index (*.LVL0)
.uleb128 .LVL1-.LVL0 # Location list length (*.LLST0)
.uleb128 0x1 # Location expression size
.byte 0x61 # DW_OP_reg17
...
.byte 0 # DW_LLE_end_of_list (*.LLST0)
and in this case we don't ICE, the DW_AT_GNU_locviews attributes aren't
emitted at all.
With just -gvariable-location-views -gdwarf-5 -gsplit-dwarf (and the patch
I've posted so that it doesn't ICE):
.uleb128 0 # DW_AT_location (*.LLST0)
.long .LVUS0-.Ldebug_loc0 # DW_AT_GNU_locviews
...
.section .debug_loclists.dwo,"e",@progbits
.long .Ldebug_loc3-.Ldebug_loc2 # Length of Location Lists
.Ldebug_loc2:
.value 0x5 # DWARF version number
.byte 0x8 # Address Size
.byte 0 # Segment Size
.long 0x3 # Offset Entry Count
.Ldebug_loc0:
.long .LLST0-.Ldebug_loc0
.long .LLST1-.Ldebug_loc0
.long .LLST2-.Ldebug_loc0
.LVUS0:
.uleb128 0 # View list begin (*.LVUS0)
.uleb128 .LVU6 # View list end (*.LVUS0)
.uleb128 .LVU6 # View list begin (*.LVUS0)
.uleb128 0 # View list end (*.LVUS0)
.LLST0:
.byte 0x3 # DW_LLE_startx_length (*.LLST0)
.uleb128 0x2 # Location list range start index (*.LVL0)
.uleb128 .LVL1-.LVL0 # Location list length (*.LLST0)
.uleb128 0x1 # Location expression size
.byte 0x61 # DW_OP_reg17
.byte 0x3 # DW_LLE_startx_length (*.LLST0)
.uleb128 0 # Location list range start index (*.LVL1)
.uleb128 .LFE0-.LVL1 # Location list length (*.LLST0)
.uleb128 0x6 # Location expression size
.byte 0xa3 # DW_OP_entry_value
.uleb128 0x3
.byte 0xa5 # DW_OP_regval_type
.uleb128 0x11
.uleb128 0x19
.byte 0x9f # DW_OP_stack_value
.byte 0 # DW_LLE_end_of_list (*.LLST0)
In order to use DW_FORM_loclistx .uleb128 for the DW_AT_GNU_locviews,
we'd need to emit .long .LVUS0-.Ldebug_loc0 etc. next to the
.LLST0-.Ldebug_loc0 in the section offsets table at .Ldebug_loc0,
but I'd expect debug info consumers to assume that anything listed
in the offset table is actually a valid DW_LLE_* sequence, which is not the
case for the .LVUS* labels.
Note the
.long .LVUS0-.Ldebug_loc0 # DW_AT_GNU_locviews
looks weird, at least with the patch it is given DW_FORM_sec_offset, but
because it is a difference between .LVUS0-.Ldebug_loc0, it is actually not a
sec offset. Shall it use a different form in that case?
Alex?
Jakub
