From a809d8a737da1ccebcd93065fc57fc0f4d94894a Mon Sep 17 00:00:00 2001 From: Marek Polacek Date: Fri, 2 Apr 2021 17:11:32 -0400 Subject: [PATCH] c++: GC during late parsing collects live data [PR91416] Coming back to : This is a crash that points to a GC problem. Consider this test: __attribute__ ((unused)) struct S { S() { } } s; We're parsing a simple-declaration. While parsing the decl specs, we parse the attribute, which means creating a TREE_LIST using ggc_alloc_*. A function body is a complete-class context so when parsing the member-specification of this class-specifier, we parse the bodies of the functions we'd queued in cp_parser_late_parsing_for_member. This then leads to this call chain: cp_parser_function_definition_after_declarator -> expand_or_defer_fn -> expand_or_defer_fn_1 -> maybe_clone_body -> expand_or_defer_fn -> cgraph_node::finalize_function -> ggc_collect. In this test, the ggc_collect call collects the TREE_LIST we had allocated, and a crash duly ensues. I couldn't do what Richard suggested, that is, attach the attribute list to struct S, because we don't pass decl_specs from cp_parser_type_specifier down to cp_parser_class_specifier. Therefore I've attempted to do "push the decl_specifiers onto a vec that is a GC root", except I couldn't really push the decl_specifiers, because first I'd have to mark cp_decl_specifier_seq with GTY(()) and even that wouldn't be enough for me to be able to create static GTY(()) vec But here we only care about cp_decl_specifier_seq::attributes, so the patch is just this. I've also extended the test so now we test a nested class too. gcc/cp/ChangeLog: PR c++/91416 * parser.c: Create a GC root for attributes in a decl specifier. (cp_parser_type_specifier): Push/pop ->attributes onto/from it. gcc/testsuite/ChangeLog: PR c++/91416 * g++.dg/other/gc7.C: New test. --- gcc/cp/parser.c | 9 +++++++++ gcc/testsuite/g++.dg/other/gc7.C | 16 ++++++++++++++++ 2 files changed, 25 insertions(+) create mode 100644 gcc/testsuite/g++.dg/other/gc7.C diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c index 808e5b6..c915d64 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -18346,6 +18346,11 @@ cp_parser_explicit_specialization (cp_parser* parser) --parser->num_template_parameter_lists; } +/* Preserve the attributes across a garbage collect (by making it a GC + root), which can occur when parsing a member function. */ + +static GTY(()) vec *cp_parser_decl_specs_attrs; + /* Parse a type-specifier. type-specifier: @@ -18438,8 +18443,12 @@ cp_parser_type_specifier (cp_parser* parser, /* Parse tentatively so that we can back up if we don't find a class-specifier. */ cp_parser_parse_tentatively (parser); + if (decl_specs->attributes) + vec_safe_push (cp_parser_decl_specs_attrs, decl_specs->attributes); /* Look for the class-specifier. */ type_spec = cp_parser_class_specifier (parser); + if (decl_specs->attributes) + cp_parser_decl_specs_attrs->pop (); invoke_plugin_callbacks (PLUGIN_FINISH_TYPE, type_spec); /* If that worked, we're done. */ if (cp_parser_parse_definitely (parser)) diff --git a/gcc/testsuite/g++.dg/other/gc7.C b/gcc/testsuite/g++.dg/other/gc7.C new file mode 100644 index 0000000..ab436ba --- /dev/null +++ b/gcc/testsuite/g++.dg/other/gc7.C @@ -0,0 +1,16 @@ +// PR c++/91416 - GC during late parsing collects live data. +// { dg-do compile } +// { dg-options "--param ggc-min-heapsize=0 --param ggc-min-expand=0" } + +__attribute__ ((unused)) struct S { + S() { } +} s; + +__attribute__ ((unused)) struct X { + void fn () + { + __attribute__ ((unused)) struct N { + N() { } + } n; + } +} x; -- 2.7.4