Re: [PATCH v2 03/24] virtio: allow __virtioXX, __leXX in config space

On Tue, Aug 04, 2020 at 04:23:40PM +0200, Cornelia Huck wrote:

On Mon, 3 Aug 2020 16:58:46 -0400
"Michael S. Tsirkin" [off-list ref] wrote:

quoted

Currently all config space fields are of the type __uXX.
This confuses people and some drivers (notably vdpa)
access them using CPU endian-ness - which only
works well for legacy or LE platforms.

Update virtio_cread/virtio_cwrite macros to allow __virtioXX
and __leXX field types. Follow-up patches will convert
config space to use these types.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/linux/virtio_config.h | 50 +++++++++++++++++++++++++++++++++--
 1 file changed, 48 insertions(+), 2 deletions(-)

(...)

quoted

@@ -287,12 +288,57 @@ static inline __virtio64 cpu_to_virtio64(struct virtio_device *vdev, u64 val)
 	return __cpu_to_virtio64(virtio_is_little_endian(vdev), val);
 }
 
+/*
+ * Only the checker differentiates between __virtioXX and __uXX types. But we
+ * try to share as much code as we can with the regular GCC build.
+ */
+#if !defined(CONFIG_CC_IS_GCC) && !defined(__CHECKER__)
+
+/* Not a checker - we can keep things simple */
+#define __virtio_native_typeof(x) typeof(x)
+
+#else
+
+/*
+ * We build this out of a couple of helper macros in a vain attempt to
+ * help you keep your lunch down while reading it.
+ */

It might help with the lunch, but it still gives a slight queasiness.
No ideas for a better version, though.

A later patch fixes this. Hopefully :)

quoted

+#define __virtio_pick_value(x, type, then, otherwise)			\
+	__builtin_choose_expr(__same_type(x, type), then, otherwise)
+
+#define __virtio_pick_type(x, type, then, otherwise)			\
+	__virtio_pick_value(x, type, (then)0, otherwise)
+
+#define __virtio_pick_endian(x, x16, x32, x64, otherwise)			\
+	__virtio_pick_type(x, x16, __u16,					\
+		__virtio_pick_type(x, x32, __u32,				\
+			__virtio_pick_type(x, x64, __u64,			\
+				otherwise)))
+
+#define __virtio_native_typeof(x) typeof(					\
+	__virtio_pick_type(x, __u8, __u8,					\
+		__virtio_pick_endian(x, __virtio16, __virtio32, __virtio64,	\
+			__virtio_pick_endian(x, __le16, __le32, __le64,		\
+				__virtio_pick_endian(x, __u16, __u32, __u64,	\
+					/* No other type allowed */		\
+					(void)0)))))
+
+#endif
+
+#define __virtio_native_type(structname, member) \
+	__virtio_native_typeof(((structname*)0)->member)
+
+#define __virtio_typecheck(structname, member, val) \
+		/* Must match the member's type, and be integer */ \
+		typecheck(__virtio_native_type(structname, member), (val))
+
+

Acked-by: Cornelia Huck <cohuck@redhat.com>

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