[PATCHv3,5/7] gdb: ensure all targets are popped before an inferior is destructed

Message ID 2e7400a931704b3b3f366d8c5b7c5d40c0931da9.1668789658.git.aburgess@redhat.com
State New
Headers
Series gdb: fix target_ops reference count for some cases |

Commit Message

Andrew Burgess Nov. 18, 2022, 4:42 p.m. UTC
  Now that the inferiors target_stack automatically manages target
reference counts, we might think that we don't need to unpush targets
when an inferior is deleted...

...unfortunately that is not the case.  The inferior::unpush function
can do some work depending on the type of target, so it is important
that we still pass through this function.

To ensure that this is the case, in this commit I've added an assert
to inferior::~inferior that ensures the inferior's target_stack is
empty (except for the ever present dummy_target).

I've then added a pop_all_targets call to delete_inferior, otherwise
the new assert will fire in, e.g. the gdb.python/py-inferior.exp test.
---
 gdb/inferior.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
  

Patch

diff --git a/gdb/inferior.c b/gdb/inferior.c
index 4bad2198af7..f4b9828a425 100644
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -70,6 +70,15 @@  inferior::~inferior ()
 {
   inferior *inf = this;
 
+  /* Before the inferior is deleted, all target_ops should be popped from
+     the target stack, this leaves just the dummy_target behind.  If this
+     is not done, then any target left in the target stack will be left
+     with an artificially high reference count.  As the dummy_target is
+     still on the target stack then we are about to loose a reference to
+     that target, leaving its reference count artificially high.  However,
+     this is not critical as the dummy_target is a singleton.  */
+  gdb_assert (m_target_stack.top ()->stratum () == dummy_stratum);
+
   m_continuations.clear ();
   target_desc_info_free (inf->tdesc_info);
 }
@@ -230,6 +239,12 @@  delete_inferior (struct inferior *inf)
 
   gdb::observers::inferior_removed.notify (inf);
 
+  /* Pop all targets now, this ensures that inferior::unpush is called
+     correctly.  As pop_all_targets ends up making a temporary switch to
+     inferior INF then we need to make this call before we delete the
+     program space, which we do below.  */
+  inf->pop_all_targets ();
+
   /* If this program space is rendered useless, remove it. */
   if (inf->pspace->empty ())
     delete inf->pspace;