struct packed: add fallback byte array implementation, use gcc_struct on Windows, unit tests

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

gdb/Makefile.in

@@ -464,6 +464,7 @@ SELFTESTS_SRCS = \
 	unittests/offset-type-selftests.c \
 	unittests/observable-selftests.c \
 	unittests/optional-selftests.c \
+	unittests/packed-selftests.c \
 	unittests/parallel-for-selftests.c \
 	unittests/parse-connection-spec-selftests.c \
 	unittests/path-join-selftests.c \

gdb/infrun.c

@@ -3971,6 +3971,16 @@ prepare_for_detach (void)
     }
 }
 
+/* If all-stop, but there exists a non-stop target, stop all threads
+   now that we're presenting the stop to the user.  */
+
+static void
+stop_all_threads_if_all_stop_mode ()
+{
+  if (!non_stop && exists_non_stop_target ())
+    stop_all_threads ("presenting stop to user in all-stop");
+}
+
 /* Wait for control to return from inferior to debugger.
 
    If inferior gets a signal, we may decide to start it up again
@@ -4017,6 +4027,8 @@ wait_for_inferior (inferior *inf)
 	break;
     }
 
+  stop_all_threads_if_all_stop_mode ();
+
   /* No error, don't finish the state yet.  */
   finish_state.release ();
 }
@@ -4240,6 +4252,8 @@ fetch_inferior_event ()
 	    bool should_notify_stop = true;
 	    int proceeded = 0;
 
+	    stop_all_threads_if_all_stop_mode ();
+
 	    clean_up_just_stopped_threads_fsms (ecs);
 
 	    if (thr != nullptr && thr->thread_fsm () != nullptr)
@@ -8138,11 +8152,6 @@ stop_waiting (struct execution_control_state *ecs)
 
   /* Let callers know we don't want to wait for the inferior anymore.  */
   ecs->wait_some_more = 0;
-
-  /* If all-stop, but there exists a non-stop target, stop all
-     threads now that we're presenting the stop to the user.  */
-  if (!non_stop && exists_non_stop_target ())
-    stop_all_threads ("presenting stop to user in all-stop");
 }
 
 /* Like keep_going, but passes the signal to the inferior, even if the

gdb/testsuite/gdb.threads/step-N-all-progress.c

@@ -0,0 +1,49 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2022 Free Software Foundation, Inc.
+
+   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 <pthread.h>
+#include <assert.h>
+#include <stdlib.h>
+
+static pthread_barrier_t barrier;
+
+static void *
+thread_func (void *arg)
+{
+  pthread_barrier_wait (&barrier);
+  return NULL;
+}
+
+int
+main ()
+{
+  pthread_t thread;
+  int ret;
+
+  pthread_barrier_init (&barrier, NULL, 2);
+
+  /* We run to this line below, and then issue "next 3".  That should
+     step over the 3 lines below and land on the return statement.  If
+     GDB prematurely stops the thread_func thread after the first of
+     the 3 nexts (and never resumes it again), then the join won't
+     ever return.  */
+  pthread_create (&thread, NULL, thread_func, NULL); /* set break here */
+  pthread_barrier_wait (&barrier);
+  pthread_join (thread, NULL);
+
+  return 0;
+}

gdb/testsuite/gdb.threads/step-N-all-progress.exp

@@ -0,0 +1,59 @@
+# Copyright 2022 Free Software Foundation, Inc.
+
+# 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/>.
+
+# Test that with "next N", all threads are resumed at each of the N
+# steps.  GDB used to have a bug where in target-non-stop targets, and
+# in all-stop mode, after the first "next" (or "step/stepi/nexti"),
+# GDB would prematurely stop all threads.  For the subsequent N-1
+# steps, only the stepped thread would continue running, while all the
+# other threads would remain stopped.
+
+standard_testfile
+
+if { [build_executable "failed to prepare" $testfile \
+	  $srcfile {debug pthreads}] == -1 } {
+    return
+}
+
+proc test {non-stop target-non-stop} {
+    save_vars ::GDBFLAGS {
+	append ::GDBFLAGS " -ex \"maintenance set target-non-stop ${target-non-stop}\""
+	append ::GDBFLAGS " -ex \"set non-stop ${non-stop}\""
+	clean_restart $::binfile
+    }
+
+    if { ![runto_main] } {
+	return
+    }
+
+    set lineno [gdb_get_line_number "set break here"]
+
+    gdb_breakpoint $lineno
+
+    gdb_continue_to_breakpoint "break here"
+
+    gdb_test "next 3" "return 0;"
+}
+
+foreach_with_prefix non-stop {off on} {
+    foreach_with_prefix target-non-stop {off on} {
+	if {${non-stop} == "on" && ${target-non-stop} == "off"} {
+	    # Invalid combination.
+	    continue
+	}
+
+	test ${non-stop} ${target-non-stop}
+    }
+}

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);
+}

gdbsupport/packed.h

@@ -27,6 +27,26 @@
    bit-fields (and ENUM_BITFIELD), when the fields must have separate
    memory locations to avoid data races.  */
 
+/* There are two implementations here -- one standard compliant, using
+   a byte array for internal representation, and another that relies on
+   bitfields and attribute packed (and attribute gcc_struct on
+   Windows).  The latter is preferable, as it is more convenient to
+   debug -- an enum wrapped in struct packed is printed by GDB as an
+   enum -- but may not work on all compilers.  */
+
+/* Clang does not support attribute gcc_struct.  */
+#if defined _WIN32 && defined __clang__
+# define PACKED_USE_ARRAY 1
+#else
+# define PACKED_USE_ARRAY 0
+#endif
+
+#if !PACKED_USE_ARRAY && defined _WIN32
+# define ATTRIBUTE_GCC_STRUCT  __attribute__((__gcc_struct__))
+#else
+# define ATTRIBUTE_GCC_STRUCT
+#endif
+
 template<typename T, size_t Bytes = sizeof (T)>
 struct packed
 {
@@ -35,7 +55,18 @@ public:
 
   packed (T val)
   {
+    gdb_static_assert (sizeof (size_t) >= sizeof (T));
+
+#if PACKED_USE_ARRAY
+    size_t tmp = val;
+    for (int i = (Bytes - 1); i >= 0; --i)
+      {
+	m_bytes[i] = tmp & 0xff;
+	tmp >>= 8;
+      }
+#else
     m_val = val;
+#endif
 
     /* Ensure size and aligment are what we expect.  */
     gdb_static_assert (sizeof (packed) == Bytes);
@@ -53,44 +84,78 @@ public:
 
   operator T () const noexcept
   {
+#if PACKED_USE_ARRAY
+    size_t tmp = 0;
+    for (int i = 0;;)
+      {
+	tmp |= m_bytes[i];
+	if (++i == Bytes)
+	  break;
+	tmp <<= 8;
+      }
+    return (T) tmp;
+#else
     return m_val;
+#endif
   }
 
 private:
+#if PACKED_USE_ARRAY
+  gdb_byte m_bytes[Bytes];
+#else
   T m_val : (Bytes * HOST_CHAR_BIT) ATTRIBUTE_PACKED;
-};
+#endif
+} ATTRIBUTE_GCC_STRUCT;
 
-/* Add some comparisons between std::atomic<packed<T>> and T.  We need
-   this because the regular comparisons would require two implicit
-   conversions to go from T to std::atomic<packed<T>>:
+/* Add some (non-atomic) comparisons between std::atomic<packed<T>>
+   and packed<T> and T.  We need this because even though
+   std::atomic<T> doesn't define these operators, the relational
+   expressions still work via implicit conversions.  Thos wouldn't
+   work when wrapped in packed without these operators, because we'd
+   require two implicit conversions to go from T to packed<T> to
+   std::atomic<packed<T>> (and back), and C++ only does one.  */
 
-     T         -> packed<T>
-     packed<T> -> std::atomic<packed<T>>
+#define PACKED_ATOMIC_OP(OP)						\
+  template<typename T, size_t Bytes>					\
+  bool operator OP (const std::atomic<packed<T, Bytes>> &lhs,		\
+		    const std::atomic<packed<T, Bytes>> &rhs)		\
+  {									\
+    return lhs.load () OP rhs.load ();					\
+  }									\
+									\
+  template<typename T, size_t Bytes>					\
+  bool operator OP (T lhs, const std::atomic<packed<T, Bytes>> &rhs)	\
+  {									\
+    return lhs OP rhs.load ();						\
+  }									\
+									\
+  template<typename T, size_t Bytes>					\
+  bool operator OP (const std::atomic<packed<T, Bytes>> &lhs, T rhs)	\
+  {									\
+    return lhs.load () OP rhs;						\
+  }									\
+									\
+  template<typename T, size_t Bytes>					\
+  bool operator OP (const std::atomic<packed<T, Bytes>> &lhs,		\
+		    packed<T, Bytes> rhs)				\
+  {									\
+    return lhs.load () OP rhs;						\
+  }									\
+									\
+  template<typename T, size_t Bytes>					\
+  bool operator OP (packed<T, Bytes> lhs,				\
+		    const std::atomic<packed<T, Bytes>> &rhs)		\
+  {									\
+    return lhs OP rhs.load ();						\
+  }
 
-   and C++ only does one.  */
+PACKED_ATOMIC_OP (==)
+PACKED_ATOMIC_OP (!=)
+PACKED_ATOMIC_OP (>)
+PACKED_ATOMIC_OP (<)
+PACKED_ATOMIC_OP (>=)
+PACKED_ATOMIC_OP (<=)
 
-template<typename T, size_t Bytes>
-bool operator== (T lhs, const std::atomic<packed<T, Bytes>> &rhs)
-{
-  return lhs == rhs.load ();
-}
-
-template<typename T, size_t Bytes>
-bool operator== (const std::atomic<packed<T, Bytes>> &lhs, T rhs)
-{
-  return lhs.load () == rhs;
-}
-
-template<typename T, size_t Bytes>
-bool operator!= (T lhs, const std::atomic<packed<T, Bytes>> &rhs)
-{
-  return !(lhs == rhs);
-}
-
-template<typename T, size_t Bytes>
-bool operator!= (const std::atomic<packed<T, Bytes>> &lhs, T rhs)
-{
-  return !(lhs == rhs);
-}
+#undef PACKED_ATOMIC_OP
 
 #endif