gdb_vecs.h: Avoid self move assign

While working on another patch I ran into an issue with
unordered_remove (in gdb_vecs.h), where removing the last item of the
vector can cause a self move assign.

When compiling the C++ standard library in debug mode (with
-D_GLIBCXX_DEBUG=1) this causes an error to trigger.

I've fixed the issue in this patch and provided a unit test.

The provided unit test includes an assignment operator which checks
for self move assign, this removes the need to compile with
-D_GLIBCXX_DEBUG=1 in order to spot the bug.  If you're keen to see
the error reported from the C++ standard library then remove operator=
from the unit test and recompile GDB with -D_GLIBCXX_DEBUG=1.

gdb/ChangeLog:

	* Makefile.in (SUBDIR_UNITTESTS_SRCS): Add new file to the list.
	* unittests/vec-utils-selftests.c: New file.
	* gdbsupport/gdb_vecs.h (unordered_remove): Avoid self move assign.

Change-Id: I80247b20cd5212038117db7412865f5e6a9257cd

1 files changed, 2 insertions, 1 deletions

diff --git a/gdb/gdbsupport/gdb_vecs.h b/gdb/gdbsupport/gdb_vecs.h
index e87ebe26e99..e8af624770d 100644
--- a/gdb/gdbsupport/gdb_vecs.h
+++ b/gdb/gdbsupport/gdb_vecs.h
@@ -51,7 +51,8 @@ unordered_remove (std::vector<T> &vec, typename std::vector<T>::iterator it)
   gdb_assert (it >= vec.begin () && it < vec.end ());
 
   T removed = std::move (*it);
-  *it = std::move (vec.back ());
+  if (it != vec.end () - 1)
+    *it = std::move (vec.back ());
   vec.pop_back ();
 
   return removed;