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[PULL,v2,03/18] compiler: rework BUG_ON using a struct

Message ID 1485447262-27014-4-git-send-email-mst@redhat.com
State New
Headers show

Commit Message

Michael S. Tsirkin Jan. 26, 2017, 4:15 p.m. UTC 
There are theoretical concerns that some compilers might not trigger
build failures on attempts to define an array of size (x ? -1 : 1) where
x is a variable 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>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
---
 include/qemu/compiler.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
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Patch

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 7512082..1da500e 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:(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)