[PATCH v3 02/32] Disable clang warnings

[Karim Taha <kariem.taha2.7@gmail.com>]

From: Kyle Evans <kevans@FreeBSD.org>

Implement PRAGMA_DISABLE_PACKED_WARNING and PRAGMA_REENABLE_PACKED_WARNING macros in include/qemu/compiler.h.

Signed-off-by: Kyle Evans <kevans@FreeBSD.org>
Signed-off-by: Karim Taha <kariem.taha2.7@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/qemu/compiler.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index a309f90c76..b037442518 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -22,6 +22,36 @@
 #define QEMU_EXTERN_C extern
 #endif
 
+/*
+ * Tricky points:
+ * - Use __builtin_choose_expr to avoid type promotion from ?:,
+ * - Invalid sizes result in a compile time error stemming from
+ *   the fact that abort has no parameters.
+ * - It's easier to use the endian-specific unaligned load/store
+ *   functions than host-endian unaligned load/store plus tswapN.
+ * - The pragmas are necessary only to silence a clang false-positive
+ *   warning: see https://bugs.llvm.org/show_bug.cgi?id=39113 .
+ * - We have to disable -Wpragmas warnings to avoid a complaint about
+ *   an unknown warning type from older compilers that don't know about
+ *   -Waddress-of-packed-member.
+ * - gcc has bugs in its _Pragma() support in some versions, eg
+ *   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83256 -- so we only
+ *   include the warning-suppression pragmas for clang
+ */
+#ifdef __clang__
+#define PRAGMA_DISABLE_PACKED_WARNING                                   \
+    _Pragma("GCC diagnostic push");                                     \
+    _Pragma("GCC diagnostic ignored \"-Wpragmas\"");                    \
+    _Pragma("GCC diagnostic ignored \"-Waddress-of-packed-member\"")
+
+#define PRAGMA_REENABLE_PACKED_WARNING          \
+    _Pragma("GCC diagnostic pop")
+
+#else
+#define PRAGMA_DISABLE_PACKED_WARNING
+#define PRAGMA_REENABLE_PACKED_WARNING
+#endif
+
 #if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
 # define QEMU_PACKED __attribute__((gcc_struct, packed))
 #else
-- 
2.40.0