DWARF5 .debug_loclists support

On Thu, Oct 20, 2016 at 01:36:12AM +0200, Jakub Jelinek wrote:
> This patch adds .debug_loclists and .debug_loclists.dwo
> support for -gdwarf-5 and -gdwarf-5 -gsplit-dwarf.
> The decrease of section size from .debug_loc section to .debug_loclists
> is really nice.
> 
> The patch doesn't handle -gdwarf-5 -gsplit-dwarf on targets where assembler
> doesn't support .uleb128, because in that case we really can't use
> DW_LLE_startx_length (no way to emit uleb128 region sizes - we don't have
> accurate instruction length computations) - we should use DW_LLE_startx_endx
> in that case, but would need .debug_addr entries not just for the region
> starts, but ends.  Cary, could you resolve this incrementally (and, do you
> plan to convert other -gsplit-dwarf support parts to DWARF 5 for -gdwarf-5)?

I'd also note that at least for the have_multiple_function_sections and
defined(HAVE_AS_LEB128) case, for -gdwarf-5 -gsplit-dwarf we could also try
to optimize the amount of .debug_addr entries, just put the base address in
that case into .debug_addr (isn't it already there in that case)
and use DW_LLE_offset_pair relative to that base.  But -gsplit-dwarf isn't a
priority for me, nor I know where the additional dwo tooling lives,
so I don't want to spend too much time on it.

> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

> +	  dw2_asm_output_data (1, DWARF2_ADDR_SIZE, "Address Size");
> +	  dw2_asm_output_data (1, 0, "Segment Size");
> +	  if (dwarf_split_debug_info)
> +	    dw2_asm_output_data (4, dwarf_split_debug_info ? loc_list_idx : 0,
> +				 "Offset Entry Count");

When working on .debug_rnglists support, I've noticed the above is a
mistake, obviously "Offset Entry Count" of 0 has to be emitted even for
-gdwarf-5 -gno-split-dwarf.  Here is updated patch with that fixed
(removed if (dwarf_split_debug_info) line and reindented the next 2 lines):

2016-10-20  Jakub Jelinek  <jakub@redhat.com>

	* dwarf2out.h (enum dw_val_class): Add dw_val_class_loclistsptr.
	* dwarf2out.c (struct dw_loc_list_struct): Change emitted field
	from bool to 1-bit uchar bitfield.  Add num_assigned and
	offset_emitted bitfields.
	(dw_val_equal_p): Compare v.val_lbl_id rather than v.val_unsigned
	for dw_val_class_lineptr and dw_val_class_macptr.  Handle
	dw_val_class_loclistsptr.
	(new_addr_loc_descr): Fix up formatting.
	(DEBUG_LOCLISTS_SECTION, DEBUG_DWO_LOCLISTS_SECTION): Define.
	(add_AT_low_high_pc): Fix up formatting.
	(add_AT_loclistsptr): New function.
	(AT_lbl): Allow dw_val_class_loclistsptr.
	(print_dw_val, attr_checksum, attr_checksum_ordered, same_dw_val_p):
	Handle dw_val_class_loclistsptr.
	(loc_list_idx): New variable.
	(output_loclists_offsets): New function.
	(size_of_die): For dw_val_class_loc_list -gsplit-dwarf -gdwarf-5
	add size_of_uleb128 of the index.  Drop never used
	dwarf_split_debug_info AT_index handling.  Handle
	dw_val_class_loclistsptr.
	(value_format): Return DW_FORM_loclistsx for dw_val_class_loc_list
	if -gsplit-dwarf -gdwarf-5.  Handle dw_val_class_loclistsptr.
	(output_loc_list): Handle DWARF 5 .debug_loclists* format.
	(output_loc_list_offset): Handle -gsplit-dwarf -gdwarf-5
	DW_FORM_loclistx indexes.
	(output_attr_index_or_value): Fix up formatting.  Don't handle
	dw_val_class_loc_list here.
	(output_die): Formatting fixes.  Handle dw_val_class_loclistsptr.
	For dw_val_class_loc_list call output_loc_list_offset rather than
	output_attr_index_or_value.
	(init_sections_and_labels): For -gdwarf-5 use .debug_loclists
	or .debug_loclists.dwo section name for debug_loc_section.
	(resolve_addr_in_expr): Formatting fix.
	(index_location_lists): Likewise.
	(assign_location_list_indexes): New function.
	(dwarf2out_finish): If there are any location lists, for
	-gsplit-dwarf -gdwarf-5 add DW_AT_loclists_base attribute.  Call
	index_location_lists only if have_location_lists.  Call
	assign_location_list_indexes for -gsplit-dwarf -gdwarf-5.  Emit
	.debug_loclists{,.dwo} section header for -gdwarf-5, for -gdwarf-5
	-gsplit-dwarf also emit offset table.

	Jakub

DWARF5 .debug_loclists support

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