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From: Pedro Alves <palves@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] struct packed: Add fallback byte array implementation Date: Mon, 25 Jul 2022 15:12:20 +0000 (GMT) [thread overview] Message-ID: <20220725151220.C4D79383B7A4@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b669667d0749ccf8d70792bb086f41904157e54d commit b669667d0749ccf8d70792bb086f41904157e54d Author: Pedro Alves <pedro@palves.net> Date: Tue Jul 19 00:26:33 2022 +0100 struct packed: Add fallback byte array implementation Attribute gcc_struct is not implemented in Clang targeting Windows, so add a fallback standard-conforming implementation based on arrays. I ran the testsuite on x86_64 GNU/Linux with this implementation forced, and saw no regressions. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29373 Change-Id: I023315ee03622c59c397bf4affc0b68179c32374 Diff: --- gdbsupport/packed.h | 51 ++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 48 insertions(+), 3 deletions(-) diff --git a/gdbsupport/packed.h b/gdbsupport/packed.h index d721b02c056..dbece2a29aa 100644 --- a/gdbsupport/packed.h +++ b/gdbsupport/packed.h @@ -28,9 +28,27 @@ bit-fields (and ENUM_BITFIELD), when the fields must have separate memory locations to avoid data races. */ -/* We need gcc_struct on Windows GCC, as otherwise the size of e.g., - "packed<int, 1>" will be larger than what we want. */ -#if defined _WIN32 +/* 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 when + debugging GDB -- printing a struct packed variable prints its field + using its natural type, which is particularly useful if the type is + an enum -- but may not work on all compilers. */ + +/* Clang targeting Windows does not support attribute gcc_struct, so + we use the alternative byte array implemention there. */ +#if defined _WIN32 && defined __clang__ +# define PACKED_USE_ARRAY 1 +#else +# define PACKED_USE_ARRAY 0 +#endif + +/* For the preferred implementation, we need gcc_struct on Windows, as + otherwise the size of e.g., "packed<int, 1>" will be larger than + what we want. Clang targeting Windows does not support attribute + gcc_struct. */ +#if !PACKED_USE_ARRAY && defined _WIN32 && !defined __clang__ # define ATTRIBUTE_GCC_STRUCT __attribute__((__gcc_struct__)) #else # define ATTRIBUTE_GCC_STRUCT @@ -44,7 +62,18 @@ public: packed (T val) { + gdb_static_assert (sizeof (ULONGEST) >= sizeof (T)); + +#if PACKED_USE_ARRAY + ULONGEST tmp = val; + for (int i = (Bytes - 1); i >= 0; --i) + { + m_bytes[i] = (gdb_byte) tmp; + tmp >>= HOST_CHAR_BIT; + } +#else m_val = val; +#endif /* Ensure size and aligment are what we expect. */ gdb_static_assert (sizeof (packed) == Bytes); @@ -62,11 +91,27 @@ public: operator T () const noexcept { +#if PACKED_USE_ARRAY + ULONGEST tmp = 0; + for (int i = 0;;) + { + tmp |= m_bytes[i]; + if (++i == Bytes) + break; + tmp <<= HOST_CHAR_BIT; + } + 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 }; /* Add some comparisons between std::atomic<packed<T>> and packed<T>
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