[{"id":3683700,"web_url":"http://patchwork.ozlabs.org/comment/3683700/","msgid":"","list_archive_url":null,"date":"2026-04-28T19:57:38","subject":"Re: [PATCH v2] c++: Improve -fdump-lang-class output","submitter":{"id":14370,"url":"http://patchwork.ozlabs.org/api/people/14370/","name":"Marek Polacek","email":"polacek@redhat.com"},"content":"On Tue, Apr 28, 2026 at 05:54:50PM +0100, Peter Damianov wrote:\n> When I was researching to write my blogpost about vtables:\n> https://peter0x44.github.io/posts/vtables-itanium-abi/\n> \n> I noticed a few improvements I could make to -fdump-lang-class's output\n> \n> -fdump-lang-class prepended \"0x\" to HOST_WIDE_INT_PRINT_HEX outputs, but the\n> macro already includes that prefix, producing \"0x0x...\" in dumps.\n> \n> Some vtable entries hold signed values e.g. vcall offsets, vbase offsets,\n> offset-to-top. When expr_as_string prints those INTEGER_CSTs,\n> negative offsets appear as large (unsigned) values. Print integer vtable\n> entries as signed values, and keep expr_as_string for all other entries.\n\nNot an approval but the patch LGTM now, thanks.\n \n> gcc/cp/ChangeLog:\n> \n> \t* class.cc (dump_vtable_entry): New function.\n> \t(dump_array): Use it.\n> \t(dump_class_hierarchy_r): Drop redundant literal 0x from\n> \tHOST_WIDE_INT_PRINT_HEX formatting.\n> \t(dump_vtable): Likewise.\n> \n> Signed-off-by: Peter Damianov \n> ---\n> \n> v2: add comment to dump_vtable_entry\n> use STRIP_NOPS\n> simplify code using print_decs instead of print_dec with SIGNED\n> \n> gcc/cp/class.cc | 31 ++++++++++++++++++++++++++-----\n> 1 file changed, 26 insertions(+), 5 deletions(-)\n> \n> diff --git a/gcc/cp/class.cc b/gcc/cp/class.cc\n> index 8beeb797a08..4d2284b1891 100644\n> --- a/gcc/cp/class.cc\n> +++ b/gcc/cp/class.cc\n> @@ -167,6 +167,7 @@ static int maybe_indent_hierarchy (FILE *, int, int);\n> static tree dump_class_hierarchy_r (FILE *, dump_flags_t, tree, tree, int);\n> static void dump_class_hierarchy (tree);\n> static void dump_class_hierarchy_1 (FILE *, dump_flags_t, tree);\n> +static void dump_vtable_entry (FILE *, tree);\n> static void dump_array (FILE *, tree);\n> static void dump_vtable (tree, tree, tree);\n> static void dump_vtt (tree, tree);\n> @@ -9729,7 +9730,7 @@ dump_class_hierarchy_r (FILE *stream,\n> tree base_binfo;\n> int i;\n> \n> - fprintf (stream, \"%s (0x\" HOST_WIDE_INT_PRINT_HEX \") \",\n> + fprintf (stream, \"%s (\" HOST_WIDE_INT_PRINT_HEX \") \",\n> \t type_as_string (BINFO_TYPE (binfo), TFF_PLAIN_IDENTIFIER),\n> \t (HOST_WIDE_INT) (uintptr_t) binfo);\n> if (binfo != igo)\n> @@ -9752,7 +9753,7 @@ dump_class_hierarchy_r (FILE *stream,\n> if (BINFO_PRIMARY_P (binfo))\n> {\n> indented = maybe_indent_hierarchy (stream, indent + 3, indented);\n> - fprintf (stream, \" primary-for %s (0x\" HOST_WIDE_INT_PRINT_HEX \")\",\n> + fprintf (stream, \" primary-for %s (\" HOST_WIDE_INT_PRINT_HEX \")\",\n> \t type_as_string (BINFO_TYPE (BINFO_INHERITANCE_CHAIN (binfo)),\n> \t\t\t TFF_PLAIN_IDENTIFIER),\n> \t (HOST_WIDE_INT) (uintptr_t) BINFO_INHERITANCE_CHAIN (binfo));\n> @@ -9845,6 +9846,23 @@ dump_class_hierarchy (tree t)\n> }\n> }\n> \n> +/* Dump VALUE, a vtable entry, to STREAM. Print integer offsets as signed\n> + values. */\n> +\n> +static void\n> +dump_vtable_entry (FILE *stream, tree value)\n> +{\n> + /* Vtable offset entries are stored in the pointer-sized vtable entry\n> + type, but should be displayed as signed ptrdiff_t values. */\n> + tree cst = value;\n> + STRIP_NOPS (cst);\n> +\n> + if (TREE_CODE (cst) == INTEGER_CST)\n> + print_decs (wi::to_wide (cst), stream);\n> + else\n> + fprintf (stream, \"%s\", expr_as_string (value, TFF_PLAIN_IDENTIFIER));\n> +}\n> +\n> static void\n> dump_array (FILE * stream, tree decl)\n> {\n> @@ -9863,8 +9881,11 @@ dump_array (FILE * stream, tree decl)\n> \n> FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (DECL_INITIAL (decl)),\n> \t\t\t ix, value)\n> - fprintf (stream, \"%-4ld %s\\n\", (long)(ix * elt),\n> -\t expr_as_string (value, TFF_PLAIN_IDENTIFIER));\n> + {\n> + fprintf (stream, \"%-4ld \", (long)(ix * elt));\n> + dump_vtable_entry (stream, value);\n> + fprintf (stream, \"\\n\");\n> + }\n> }\n> \n> static void\n> @@ -9886,7 +9907,7 @@ dump_vtable (tree t, tree binfo, tree vtable)\n> if (ctor_vtbl_p)\n> \t{\n> \t if (!BINFO_VIRTUAL_P (binfo))\n> -\t fprintf (stream, \" (0x\" HOST_WIDE_INT_PRINT_HEX \" instance)\",\n> +\t fprintf (stream, \" (\" HOST_WIDE_INT_PRINT_HEX \" instance)\",\n> \t\t (HOST_WIDE_INT) (uintptr_t) binfo);\n> \t fprintf (stream, \" in %s\", type_as_string (t, TFF_PLAIN_IDENTIFIER));\n> \t}\n> -- \n> 2.54.0\n> \n\nMarek","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=hzVLzK7d;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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