struct packed: add fallback byte array implementation, use gcc_struct on Windows, unit testsusers/palves/packed

https://sourceware.org/bugzilla/show_bug.cgi?id=29373

- Windows hosts need attribute gcc_struct.

- attribute gcc_struct seemingly doesn't work with Clang, so add a
  fallback standard-conforming implementation based on arrays.

- add unit tests to make sure both implementations behave the same
  way.

- add more relational operators while at it.

Change-Id: I023315ee03622c59c397bf4affc0b68179c32374

1 files changed, 125 insertions, 0 deletions

diff --git a/gdb/unittests/packed-selftests.c b/gdb/unittests/packed-selftests.c
new file mode 100644
index 0000000..172d601
--- /dev/null
+++ b/gdb/unittests/packed-selftests.c
@@ -0,0 +1,125 @@
+/* Self tests for packed for GDB, the GNU debugger.
+
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "gdbsupport/selftest.h"
+#include "gdbsupport/packed.h"
+#include <atomic>
+
+namespace selftests {
+namespace packed_tests {
+
+gdb_static_assert (sizeof (packed<unsigned int, 1>) == 1);
+gdb_static_assert (sizeof (packed<unsigned int, 2>) == 2);
+gdb_static_assert (sizeof (packed<unsigned int, 3>) == 3);
+gdb_static_assert (sizeof (packed<unsigned int, 4>) == 4);
+
+gdb_static_assert (alignof (packed<unsigned int, 1>) == 1);
+gdb_static_assert (alignof (packed<unsigned int, 2>) == 1);
+gdb_static_assert (alignof (packed<unsigned int, 3>) == 1);
+gdb_static_assert (alignof (packed<unsigned int, 4>) == 1);
+
+/* Triviality checks.  */
+#define CHECK_TRAIT(TRAIT)			\
+  static_assert (std::TRAIT<packed<unsigned int, 1>>::value, "")
+
+#if HAVE_IS_TRIVIALLY_COPYABLE
+
+CHECK_TRAIT (is_trivially_copyable);
+CHECK_TRAIT (is_trivially_copy_constructible);
+CHECK_TRAIT (is_trivially_move_constructible);
+CHECK_TRAIT (is_trivially_copy_assignable);
+CHECK_TRAIT (is_trivially_move_assignable);
+
+#endif
+
+#undef CHECK_TRAIT
+
+/* Entry point.  */
+
+static void
+run_tests ()
+{
+  typedef packed<unsigned int, 2> packed_2;
+
+  packed_2 p1;
+  packed_2 p2 (0x0102);
+  p1 = 0x0102;
+
+  SELF_CHECK (p1 == p1);
+  SELF_CHECK (p1 == p2);
+  SELF_CHECK (p1 == 0x0102);
+  SELF_CHECK (0x0102 == p1);
+
+  SELF_CHECK (p1 != 0);
+  SELF_CHECK (0 != p1);
+
+  SELF_CHECK (p1 != 0x0103);
+  SELF_CHECK (0x0103 != p1);
+
+  SELF_CHECK (p1 != 0x01020102);
+  SELF_CHECK (0x01020102 != p1);
+
+  SELF_CHECK (p1 != 0x01020000);
+  SELF_CHECK (0x01020000 != p1);
+
+  /* Check truncation.  */
+  p1 = 0x030102;
+  SELF_CHECK (p1 == 0x0102);
+  SELF_CHECK (p1 != 0x030102);
+
+  /* Check that the custom std::atomic/packed/T relational operators
+     work as intended.  No need for fully comprehensive tests, as all
+     operators are defined in the same way, via a macro.  We just want
+     to make sure that we can (non-atomically) compare atomic-wrapped
+     packed, with packed, and with the packed underlying type.  */
+
+  std::atomic<packed<unsigned int, 2>> atomic_packed_2 (0x0102);
+
+  SELF_CHECK (atomic_packed_2 == atomic_packed_2);
+  SELF_CHECK (atomic_packed_2 == p1);
+  SELF_CHECK (p1 == atomic_packed_2);
+  SELF_CHECK (atomic_packed_2 == 0x0102u);
+  SELF_CHECK (0x0102u == atomic_packed_2);
+
+  SELF_CHECK (atomic_packed_2 >= 0x0102u);
+  SELF_CHECK (atomic_packed_2 <= 0x0102u);
+  SELF_CHECK (atomic_packed_2 > 0u);
+  SELF_CHECK (atomic_packed_2 < 0x0103u);
+  SELF_CHECK (atomic_packed_2 >= 0u);
+  SELF_CHECK (atomic_packed_2 <= 0x0102u);
+  SELF_CHECK (!(atomic_packed_2 > 0x0102u));
+  SELF_CHECK (!(atomic_packed_2 < 0x0102u));
+
+  /* Check std::atomic<packed> truncation behaves the same as without
+     std::atomic.  */
+  atomic_packed_2 = 0x030102;
+  SELF_CHECK (atomic_packed_2 == 0x0102u);
+  SELF_CHECK (atomic_packed_2 != 0x030102u);
+}
+
+} /* namespace packed_tests */
+} /* namespace selftests */
+
+void _initialize_packed_selftests ();
+void
+_initialize_packed_selftests ()
+{
+  selftests::register_test ("packed", selftests::packed_tests::run_tests);
+}