From a43f3893f6cb66dfca7f628cd159a008009ad06f Mon Sep 17 00:00:00 2001 From: Patrick Frants Date: Thu, 26 Oct 2017 22:26:08 -0400 Subject: [PATCH] Fix broken recursion detection when printing static members MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Recursion detection for static members was broken. The implementation uses a growing (and shrinking) obstack object to simulate a stack of addresses (CORE_ADDR). Pushing addresses is implemented by calling obstack_grow(), while popping is implemented by calling obstack_free(). The latter is problematic because obstack_free() expects a pointer to the base of an object. When popping elements of the stack however, obstack_free() was called with the new top, which potentially is not the same as the base of the stack. This is unintended use and the effect is that obstack->next_free and obstack->object_base members are assigned the value of the new top, which equals an empty stack. Summary: popping elements would always result in an empty stack, which breaks the recursion detection. The fix shrinks the stack using obstack_blank_fast() with a negative value as described at the bottom of this page: https://gcc.gnu.org/onlinedocs/libiberty/Extra-Fast-Growing.html "You can use obstack_blank_fast with a “negative” size argument to make the current object smaller. Just don’t try to shrink it beyond zero length—there’s no telling what will happen if you do that. Earlier versions of obstacks allowed you to use obstack_blank to shrink objects. This will no longer work." The reproducer is added to gdb.cp/classes.exp, which fails without this patch. gdb/ChangeLog: * cp-valprint.c (cp_print_value_fields): Use obstack_blank_fast to rewind obstack. gdb/testsuite/ChangeLog: * gdb.cp/classes.exp (test_static_members): Test printing Outer::instance. * gdb.cp/classes.c (struct Inner, struct Outer): New. (Inner::instance, Outer::instance): New. --- gdb/ChangeLog | 5 +++++ gdb/cp-valprint.c | 10 +++------- gdb/testsuite/ChangeLog | 7 +++++++ gdb/testsuite/gdb.cp/classes.cc | 13 +++++++++++++ gdb/testsuite/gdb.cp/classes.exp | 5 +++++ 5 files changed, 33 insertions(+), 7 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index caa64848799..1d188811210 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2017-10-26 Patrick Frants + + * cp-valprint.c (cp_print_value_fields): Use obstack_blank_fast + to rewind obstack. + 2017-10-26 Pedro Alves * remote.c (remote_async_terminal_ours_p): Delete. diff --git a/gdb/cp-valprint.c b/gdb/cp-valprint.c index fb9bfd904f7..609dabb6606 100644 --- a/gdb/cp-valprint.c +++ b/gdb/cp-valprint.c @@ -371,13 +371,9 @@ cp_print_value_fields (struct type *type, struct type *real_type, if (obstack_final_size > statmem_obstack_initial_size) { /* In effect, a pop of the printed-statics stack. */ - - void *free_to_ptr = - (char *) obstack_next_free (&dont_print_statmem_obstack) - - (obstack_final_size - statmem_obstack_initial_size); - - obstack_free (&dont_print_statmem_obstack, - free_to_ptr); + size_t shrink_bytes + = statmem_obstack_initial_size - obstack_final_size; + obstack_blank_fast (&dont_print_statmem_obstack, shrink_bytes); } if (last_set_recurse != recurse) diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 0c6c93acb03..0e2bc23d0ce 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,10 @@ +2017-10-26 Patrick Frants + + * gdb.cp/classes.exp (test_static_members): Test printing + Outer::instance. + * gdb.cp/classes.c (struct Inner, struct Outer): New. + (Inner::instance, Outer::instance): New. + 2017-10-24 Pedro Alves * gdb.base/new-ui.exp (do_test): Split "delete all breakpoints on diff --git a/gdb/testsuite/gdb.cp/classes.cc b/gdb/testsuite/gdb.cp/classes.cc index 50f0740abe7..a6508462b7e 100644 --- a/gdb/testsuite/gdb.cp/classes.cc +++ b/gdb/testsuite/gdb.cp/classes.cc @@ -665,6 +665,19 @@ void use_methods () base1 b (3); } +struct Inner +{ + static Inner instance; +}; + +struct Outer +{ + Inner inner; + static Outer instance; +}; + +Inner Inner::instance; +Outer Outer::instance; int main() diff --git a/gdb/testsuite/gdb.cp/classes.exp b/gdb/testsuite/gdb.cp/classes.exp index 9e2630acef4..374b6327912 100644 --- a/gdb/testsuite/gdb.cp/classes.exp +++ b/gdb/testsuite/gdb.cp/classes.exp @@ -602,6 +602,11 @@ proc test_static_members {} { gdb_test "print cnsi" \ "{x = 30, y = 40, static null = {x = 0, y = 0, static null = , static yy = {z = 5, static xx = {x = 1, y = 2, static null = , static yy = }}}, static yy = }" \ "print cnsi with static members" + + # Another case of infinite recursion. + gdb_test "print Outer::instance" \ + "{inner = {static instance = {static instance = }}, static instance = {inner = {static instance = {static instance = }}, static instance = }}" \ + "print recursive static member" } proc do_tests {} { -- 2.30.2