On 4/3/21 5:35 PM, Marek Polacek wrote:
On Sat, Apr 03, 2021 at 10:47:13AM -0400, Jason Merrill wrote:
On 4/2/21 9:53 PM, Marek Polacek wrote:
Coming back to
<https://gcc.gnu.org/pipermail/gcc-patches/2019-August/527699.html>:
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<cp_decl_specifier_seq *, va_gc>
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.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10.4?
gcc/cp/ChangeLog:
PR c++/91416
* parser.c: Create a GC root for attributes in a decl specifier.
(cp_parser_declaration): Free it.
(cp_parser_type_specifier): Push ->attributes onto it.
gcc/testsuite/ChangeLog:
PR c++/91416
* g++.dg/other/gc7.C: New test.
---
gcc/cp/parser.c | 7 +++++++
gcc/testsuite/g++.dg/other/gc7.C | 16 ++++++++++++++++
2 files changed, 23 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/other/gc7.C
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 808e5b61b1e..31da9f56b1b 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -13957,6 +13957,11 @@ cp_parser_declaration_seq_opt (cp_parser* parser)
}
}
+/* Preserve the attributes across a garbage collect (by making it a GC
+ root), which can occur when parsing a member function. */
+
+static GTY(()) vec<tree, va_gc> *cp_parser_decl_specs_attrs;
+
/* Parse a declaration.
declaration:
@@ -14140,6 +14145,7 @@ cp_parser_declaration (cp_parser* parser, tree
prefix_attrs)
/* Free any declarators allocated. */
obstack_free (&declarator_obstack, p);
+ vec_free (cp_parser_decl_specs_attrs);
}
/* Parse a namespace-scope declaration. */
@@ -18438,6 +18444,7 @@ 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);
+ vec_safe_push (cp_parser_decl_specs_attrs, decl_specs->attributes);
This looks like any time we see 'class' in a function we'll add another
entry to the vec, that accumulates until we finish the enclosing top-level
declaration. Let's pop the entry again after the call to
cp_parser_class_specifier, and only push/pop if there are actually any
attributes.
Ah, yeah, push/pop works here too, thanks.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10?
OK for trunk and 10 after 10.3.
-- >8 --
Coming back to
<https://gcc.gnu.org/pipermail/gcc-patches/2019-August/527699.html>:
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<cp_decl_specifier_seq *, va_gc>
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 808e5b61b1e..c915d6415de 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<tree, va_gc> *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 00000000000..ab436bac72f
--- /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;
base-commit: fc27115d6107f219e6f3dc610c99210005fe9dc5
