Re: [Qemu-devel] [RfC PATCH 2/2] qdev/prop: convert pci.c to helper macros.

[Gerd Hoffmann <kraxel@redhat.com>]

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   Hi,

>             (long)(&(_prop)->type -&((_struct *)0)->_field)) \

> This seems to be free of gcc extensions and gives more or less sane errors like:
>
> foo.c:26: error: invalid operands to binary - (have ‘long long int *’ and ‘int *’)

The "better error message" bit works.  Nice idea.  Incremental patch 
attached.

cheers,
   Gerd

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From cf4d63c456250c7e97705338c3c052fe10a5a4b6 Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Fri, 31 Jul 2009 17:36:01 +0200
Subject: [PATCH] better type check

---
 hw/qdev.h |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/hw/qdev.h b/hw/qdev.h
index 4fe534e..e2703f4 100644
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -156,10 +156,8 @@ extern PropertyInfo qdev_prop_ptr;
 extern PropertyInfo qdev_prop_macaddr;
 extern PropertyInfo qdev_prop_pci_devfn;
 
-extern int qdev_property_type_check_failed; /* undefined */
 #define typeof_field(type, field) typeof(((type *)0)->field)
-#define type_check(t1,t2) __builtin_choose_expr( \
-        __builtin_types_compatible_p(t1,t2),0,qdev_property_type_check_failed)
+#define type_check(t1,t2) ((t1*)0 - (t2*)0)
 
 #define DEFINE_PROP(_name, _state, _field, _prop, _type) { \
         .name      = (_name),                                    \
-- 
1.6.2.5