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authorPedro Alves <pedro@palves.net>2022-07-19 00:26:33 +0100
committerPedro Alves <pedro@palves.net>2022-07-19 15:44:07 +0100
commit73a029bd6037c59d10ab39518ad35d76292be54a (patch)
tree9f9864a9d103193b202d1f4e6ec9aeb63dd275ef
parent6994a75776b3a40e9a7435be8e6c5518c18bd391 (diff)
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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
-rw-r--r--gdb/Makefile.in1
-rw-r--r--gdb/unittests/packed-selftests.c125
-rw-r--r--gdbsupport/packed.h129
3 files changed, 223 insertions, 32 deletions
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 911daa2..b0daa64 100644
--- a/gdb/Makefile.in
+++ b/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 \
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);
+}
diff --git a/gdbsupport/packed.h b/gdbsupport/packed.h
index 3468cf4..d65e0bc 100644
--- a/gdbsupport/packed.h
+++ b/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;
-};
-
-/* 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>>:
-
- T -> packed<T>
- packed<T> -> std::atomic<packed<T>>
-
- and C++ only does one. */
-
-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;
-}
+#endif
+} ATTRIBUTE_GCC_STRUCT;
+
+/* 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. */
+
+#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 (); \
+ }
-template<typename T, size_t Bytes>
-bool operator!= (T lhs, const std::atomic<packed<T, Bytes>> &rhs)
-{
- return !(lhs == rhs);
-}
+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!= (const std::atomic<packed<T, Bytes>> &lhs, T rhs)
-{
- return !(lhs == rhs);
-}
+#undef PACKED_ATOMIC_OP
#endif