compiler: Add QEMU_BUILD_BUG_MSG() macro

_Static_assert() allows us to specify messages, and that may come in
handy.  Even without _Static_assert(), encouraging developers to put a
helpful message next to the QEMU_BUILD_BUG_* may make debugging easier
whenever it breaks.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20180224154033.29559-2-mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 2cbe6a4f16e91c0074b0e879bf21dcc6dac0100a..9f762695d116d8cce83436b75e3a626c33dea8bf 100644 (file)
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -82,15 +82,21 @@
         int:(x) ? -1 : 1; \
     }
 
+/* QEMU_BUILD_BUG_MSG() emits the message given if _Static_assert is
+ * supported; otherwise, it will be omitted from the compiler error
+ * message (but as it remains present in the source code, it can still
+ * be useful when debugging). */
 #if defined(CONFIG_STATIC_ASSERT)
-#define QEMU_BUILD_BUG_ON(x) _Static_assert(!(x), "not expecting: " #x)
+#define QEMU_BUILD_BUG_MSG(x, msg) _Static_assert(!(x), msg)
 #elif defined(__COUNTER__)
-#define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
+#define QEMU_BUILD_BUG_MSG(x, msg) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
     glue(qemu_build_bug_on__, __COUNTER__) __attribute__((unused))
 #else
-#define QEMU_BUILD_BUG_ON(x)
+#define QEMU_BUILD_BUG_MSG(x, msg)
 #endif
 
+#define QEMU_BUILD_BUG_ON(x) QEMU_BUILD_BUG_MSG(x, "not expecting: " #x)
+
 #define QEMU_BUILD_BUG_ON_ZERO(x) (sizeof(QEMU_BUILD_BUG_ON_STRUCT(x)) - \
                                    sizeof(QEMU_BUILD_BUG_ON_STRUCT(x)))