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
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 @@ 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 @@ struct packed 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 @@ struct packed 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