On Wed, Nov 6, 2024 at 3:36 PM Michal Jires <mji...@suse.cz> wrote:
>
> Die symbols are used for external references.
> Typically during LTO, early debug emits 'die_symbol+offset' for each
> possibly referenced DIE in future. Partitions in LTRANS phase then
> use these references.
>
> Originally die symbols are handled only in root comp_unit and
> in attributes.
>
> This patch allows die symbols to be attached to any DIE.
> References then choose closest parent with die symbol.
>
> gcc/ChangeLog:
>
> * dwarf2out.cc (dwarf2out_die_ref_for_decl):
> Choose closest parent with die_symbol.
> (output_die): Output asm label.
> (output_unit_die_symbol_list): New.
> (output_comp_unit): Output die_symbol list.
> (reset_dies): Reset all die_symbols.
> (dwarf2out_finish): Don't reset comp_unit die_symbol.
> ---
> gcc/dwarf2out.cc | 80 +++++++++++++++++++++++++++---------------------
> 1 file changed, 45 insertions(+), 35 deletions(-)
>
> diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
> index e10a5c78fe9..bf1ac45ed73 100644
> --- a/gcc/dwarf2out.cc
> +++ b/gcc/dwarf2out.cc
> @@ -6039,14 +6039,14 @@ dwarf2out_die_ref_for_decl (tree decl, const char
> **sym,
ah - here it is ...
> /* Similar to get_ref_die_offset_label, but using the "correct"
> label. */
> - *off = die->die_offset;
> - while (die->die_parent)
> + unsigned HOST_WIDE_INT unit_offset = die->die_offset;
> + while (die->die_parent && (die->comdat_type_p || !die->die_id.die_symbol))
> die = die->die_parent;
> - /* For the containing CU DIE we compute a die_symbol in
> + /* Root CU DIE always contains die_symbol computed in
> compute_comp_unit_symbol. */
> - if (die->die_tag == DW_TAG_compile_unit)
> + if (!die->comdat_type_p && die->die_id.die_symbol)
> {
> - gcc_assert (die->die_id.die_symbol != NULL);
> + *off = unit_offset - die->die_offset;
> *sym = die->die_id.die_symbol;
> return true;
> }
> @@ -10798,6 +10798,10 @@ output_die (dw_die_ref die)
> unsigned long size;
> unsigned ix;
>
> + if ((flag_generate_lto || flag_generate_offload)
> + && !die->comdat_type_p && die->die_id.die_symbol)
> + ASM_OUTPUT_LABEL (asm_out_file, die->die_id.die_symbol);
> +
> dw2_asm_output_data_uleb128 (die->die_abbrev, "(DIE (%#lx) %s)",
> (unsigned long)die->die_offset,
> dwarf_tag_name (die->die_tag));
> @@ -11228,14 +11232,41 @@ output_compilation_unit_header (enum
> dwarf_unit_type ut)
> dw2_asm_output_data (1, DWARF2_ADDR_SIZE, "Pointer Size (in bytes)");
> }
>
> +/* Output list of all die symbols in the DIE. */
> +static void
> +output_unit_die_symbol_list (dw_die_ref die)
> +{
> + if (!die->comdat_type_p && die->die_id.die_symbol)
> + {
> + const char* sym = die->die_id.die_symbol;
> + /* ??? No way to get visibility assembled without a decl. */
> + tree decl = build_decl (UNKNOWN_LOCATION, VAR_DECL,
> + get_identifier (sym), char_type_node);
> + TREE_PUBLIC (decl) = true;
> + TREE_STATIC (decl) = true;
> + DECL_ARTIFICIAL (decl) = true;
> + DECL_VISIBILITY (decl) = VISIBILITY_HIDDEN;
> + DECL_VISIBILITY_SPECIFIED (decl) = true;
> + targetm.asm_out.assemble_visibility (decl, VISIBILITY_HIDDEN);
> +#ifdef ASM_WEAKEN_LABEL
> + /* We prefer a .weak because that handles duplicates from duplicate
> + archive members in a graceful way. */
> + ASM_WEAKEN_LABEL (asm_out_file, sym);
> +#else
> + targetm.asm_out.globalize_label (asm_out_file, sym);
> +#endif
> + }
> +
> + dw_die_ref c;
> + FOR_EACH_CHILD (die, c, output_unit_die_symbol_list (c));
I'm not sure it will work this way together with the output_die hunk, instead
assemblers likely expect all this to happen close to the actual label
emission, so I suggest to only split out the visibiltiy/globalizing fancy
and emit it from output_die instead.
> +}
> +
> /* Output the compilation unit DIE and its children. */
>
> static void
> output_comp_unit (dw_die_ref die, int output_if_empty,
> const unsigned char *dwo_id)
> {
> - const char *oldsym;
> -
> /* Unless we are outputting main CU, we may throw away empty ones. */
> if (!output_if_empty && die->die_child == NULL)
> return;
> @@ -11267,34 +11298,12 @@ output_comp_unit (dw_die_ref die, int
> output_if_empty,
> : DWARF_COMPILE_UNIT_HEADER_SIZE);
> calc_die_sizes (die);
>
> - oldsym = die->die_id.die_symbol;
> -
> switch_to_section (debug_info_section);
> ASM_OUTPUT_LABEL (asm_out_file, debug_info_section_label);
> info_section_emitted = true;
>
> - /* For LTO cross unit DIE refs we want a symbol on the start of the
> - debuginfo section, not on the CU DIE. */
> - if ((flag_generate_lto || flag_generate_offload) && oldsym)
> - {
> - /* ??? No way to get visibility assembled without a decl. */
> - tree decl = build_decl (UNKNOWN_LOCATION, VAR_DECL,
> - get_identifier (oldsym), char_type_node);
> - TREE_PUBLIC (decl) = true;
> - TREE_STATIC (decl) = true;
> - DECL_ARTIFICIAL (decl) = true;
> - DECL_VISIBILITY (decl) = VISIBILITY_HIDDEN;
> - DECL_VISIBILITY_SPECIFIED (decl) = true;
> - targetm.asm_out.assemble_visibility (decl, VISIBILITY_HIDDEN);
> -#ifdef ASM_WEAKEN_LABEL
> - /* We prefer a .weak because that handles duplicates from duplicate
> - archive members in a graceful way. */
> - ASM_WEAKEN_LABEL (asm_out_file, oldsym);
> -#else
> - targetm.asm_out.globalize_label (asm_out_file, oldsym);
> -#endif
> - ASM_OUTPUT_LABEL (asm_out_file, oldsym);
> - }
> + if (flag_generate_lto || flag_generate_offload)
> + output_unit_die_symbol_list (die);
>
> /* Output debugging information. */
> output_compilation_unit_header (dwo_id
> @@ -11309,7 +11318,7 @@ output_comp_unit (dw_die_ref die, int output_if_empty,
>
> /* Leave the marks on the main CU, so we can check them in
> output_pubnames. */
> - if (oldsym)
> + if (die->die_id.die_symbol)
> unmark_dies (die);
> }
>
> @@ -32297,6 +32306,10 @@ reset_dies (dw_die_ref die)
> die->die_abbrev = 0;
> remove_AT (die, DW_AT_sibling);
>
> + /* Reset die symbols so we don't output them twice. */
> + if (!die->comdat_type_p)
> + die->die_id.die_symbol = NULL;
> +
> FOR_EACH_CHILD (die, c, reset_dies (c));
> }
>
> @@ -32388,9 +32401,6 @@ dwarf2out_finish (const char *filename)
> reset_dies (ctnode->root_die);
> }
>
> - /* Reset die CU symbol so we don't output it twice. */
> - comp_unit_die ()->die_id.die_symbol = NULL;
> -
> /* Remove DW_AT_macro and DW_AT_stmt_list from the early output. */
> remove_AT (comp_unit_die (), DW_AT_stmt_list);
> if (have_macinfo)
> --
> 2.47.0
>
