[PATCH v2 2/4] linux/stddef.h: Add sizeof_member() macro

[Kees Cook]

From: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@xxxxxxxxx>

At present we have 2 different macros to calculate the size of a member
of a struct: FIELD_SIZEOF() and sizeof_field(). As a prerequisite to
bringing uniformity to the entire kernel source tree, add sizeof_member()
macro as it is both more pleasant (not upper case) and more correct
(sizeof()-family cannot operate on bit fields; this is meant to operate
on struct members), as discussed[1].

Future patches will replace all occurrences of above macros with
sizeof_member().

[1] https://www.openwall.com/lists/kernel-hardening/2019/07/02/2

Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@xxxxxxxxx>
Link: https://lore.kernel.org/r/20190924105839.110713-2-pankaj.laxminarayan.bharadiya@xxxxxxxxx
Co-developed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/stddef.h                 | 13 ++++++++++++-
 tools/testing/selftests/bpf/bpf_util.h |  6 +++---
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/stddef.h b/include/linux/stddef.h
index 998a4ba28eba..ecadb736c853 100644
--- a/include/linux/stddef.h
+++ b/include/linux/stddef.h
@@ -27,6 +27,17 @@ enum {
  */
 #define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
 
+/**
+ * sizeof_member(TYPE, MEMBER) - get the size of a struct's member
+ *
+ * @TYPE: the target struct
+ * @MEMBER: the target struct's member
+ *
+ * Return: the size of @MEMBER in the struct definition without having a
+ * declared instance of @TYPE.
+ */
+#define sizeof_member(TYPE, MEMBER)	(sizeof(((TYPE *)0)->MEMBER))
+
 /**
  * offsetofend(TYPE, MEMBER)
  *
@@ -34,6 +45,6 @@ enum {
  * @MEMBER: The member within the structure to get the end offset of
  */
 #define offsetofend(TYPE, MEMBER) \
-	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
+	(offsetof(TYPE, MEMBER)	+ sizeof_member(TYPE, MEMBER))
 
 #endif
diff --git a/tools/testing/selftests/bpf/bpf_util.h b/tools/testing/selftests/bpf/bpf_util.h
index ec219f84e041..6b4b3e24ba9f 100644
--- a/tools/testing/selftests/bpf/bpf_util.h
+++ b/tools/testing/selftests/bpf/bpf_util.h
@@ -31,13 +31,13 @@ static inline unsigned int bpf_num_possible_cpus(void)
 # define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 #endif
 
-#ifndef sizeof_field
-#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
+#ifndef sizeof_member
+#define sizeof_member(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
 #endif
 
 #ifndef offsetofend
 #define offsetofend(TYPE, MEMBER) \
-	(offsetof(TYPE, MEMBER)	+ sizeof_field(TYPE, MEMBER))
+	(offsetof(TYPE, MEMBER)	+ sizeof_member(TYPE, MEMBER))
 #endif
 
 #endif /* __BPF_UTIL__ */
-- 
2.17.1