compiler: expression version of QEMU_BUILD_BUG_ON

QEMU_BUILD_BUG_ON uses a typedef in order to be safe
to use outside functions, but sometimes it's useful
to have a version that can be used within an expression.
Following what Linux does, introduce QEMU_BUILD_BUG_ON_ZERO
that return zero after checking condition at build time.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 057639af431db5638e421650455351d01959e0a1..e0ce9ffb2814c6b4ef1c4ac5574f3d5057efe248 100644 (file)
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -97,6 +97,9 @@
 #define QEMU_BUILD_BUG_ON(x)
 #endif
 
+#define QEMU_BUILD_BUG_ON_ZERO(x) (sizeof(QEMU_BUILD_BUG_ON_STRUCT(x)) - \
+                                   sizeof(QEMU_BUILD_BUG_ON_STRUCT(x)))
+
 #if defined __GNUC__
 # if !QEMU_GNUC_PREREQ(4, 4)
    /* gcc versions before 4.4.x don't support gnu_printf, so use printf. */