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[PULL,v2,04/18] compiler: expression version of QEMU_BUILD_BUG_ON

Message ID 1485447262-27014-5-git-send-email-mst@redhat.com
State New
Headers show

Commit Message

Michael S. Tsirkin Jan. 26, 2017, 4:15 p.m. UTC 
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>
---
 include/qemu/compiler.h | 3 +++
 1 file changed, 3 insertions(+)
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Patch

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index 1da500e..e0fb18b 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -92,6 +92,9 @@ 
 #define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
     glue(qemu_build_bug_on__, __LINE__) __attribute__((unused))
 
+#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. */