[Qemu-devel] [PATCH v3 2/4] compiler: rework BUG_ON using a struct

["Michael S. Tsirkin" <mst@redhat.com>]

There are theoretical concerns that some compilers might not trigger
build failures on attempts to define an array of size -1 and make it a
variable sized array instead. Let rewrite using a struct with a negative
bit field size instead as there are no dynamic bit field sizes.  This is
similar to what Linux does.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/qemu/compiler.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 7512082..c6f673e 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -85,9 +85,12 @@
 #define typeof_field(type, field) typeof(((type *)0)->field)
 #define type_check(t1,t2) ((t1*)0 - (t2*)0)
 
-#define QEMU_BUILD_BUG_ON(x) \
-    typedef char glue(qemu_build_bug_on__, __LINE__)[(x) ? -1 : 1] \
-        __attribute__((unused))
+#define QEMU_BUILD_BUG_ON_STRUCT(x) \
+    struct { \
+        int qemu_build_bug_on : (x) ? -1 : 1; \
+    }
+#define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
+    glue(qemu_build_bug_on__, __LINE__) __attribute__((unused))
 
 #if defined __GNUC__
 # if !QEMU_GNUC_PREREQ(4, 4)
-- 
MST