[xen staging] xen/include: import sizeof_field() macro from Linux stddef.h

[patchbot@xxxxxxx]

commit 758fae24d7b90fcfa7dffbffb5a5cab274caf3fc
Author:     Paul Durrant <pdurrant@xxxxxxxxxx>
AuthorDate: Wed Nov 25 14:06:27 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Nov 25 14:06:27 2020 +0100

    xen/include: import sizeof_field() macro from Linux stddef.h
    
    Co-locate it with the definition of offsetof() (since this is also in 
stddef.h
    in the Linux kernel source). This macro will be needed in a subsequent 
patch.
    
    Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/include/xen/compiler.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index c0e0ee9f27..676c6ea1b0 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -76,6 +76,14 @@
 
 #define offsetof(a,b) __builtin_offsetof(a,b)
 
+/**
+ * sizeof_field(TYPE, MEMBER)
+ *
+ * @TYPE: The structure containing the field of interest
+ * @MEMBER: The field to return the size of
+ */
+#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
+
 #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L
 #define alignof __alignof__
 #endif
--
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