sparse: Add __private to privatize members of structs

In C programming language, we don't have a easy way to privatize a
member of a structure. However in kernel, sometimes there is a need to
privatize a member in case of potential bugs or misuses.

Fortunately, the noderef attribute of sparse is a way to privatize a
member, as by defining a member as noderef, the address-of operator on
the member will produce a noderef pointer to that member, and if anyone
wants to dereference that kind of pointers to read or modify the member,
sparse will yell.

Based on this, __private modifier and related operation ACCESS_PRIVATE()
are introduced, which could help detect undesigned public uses of
private members of structs. Here is an example of sparse's output if it
detect an undersigned public use:

| kernel/rcu/tree.c:4453:25: warning: incorrect type in argument 1 (different modifiers)
| kernel/rcu/tree.c:4453:25:    expected struct raw_spinlock [usertype] *lock
| kernel/rcu/tree.c:4453:25:    got struct raw_spinlock [noderef] *<noident>

Also, this patch improves compiler.h a little bit by adding comments for
"#else" and "#endif".

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 00b042c49ccdac7af3262a399d33dacc88c83e25..c845356952bbf5830462b7c6d629f3be1b580f72 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -20,12 +20,14 @@
 # define __pmem                __attribute__((noderef, address_space(5)))
 #ifdef CONFIG_SPARSE_RCU_POINTER
 # define __rcu         __attribute__((noderef, address_space(4)))
-#else
+#else /* CONFIG_SPARSE_RCU_POINTER */
 # define __rcu
-#endif
+#endif /* CONFIG_SPARSE_RCU_POINTER */
+# define __private     __attribute__((noderef))
 extern void __chk_user_ptr(const volatile void __user *);
 extern void __chk_io_ptr(const volatile void __iomem *);
-#else
+# define ACCESS_PRIVATE(p, member) (*((typeof((p)->member) __force *) &(p)->member))
+#else /* __CHECKER__ */
 # define __user
 # define __kernel
 # define __safe
@@ -44,7 +46,9 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 # define __percpu
 # define __rcu
 # define __pmem
-#endif
+# define __private
+# define ACCESS_PRIVATE(p, member) ((p)->member)
+#endif /* __CHECKER__ */
 
 /* Indirect macros required for expanded argument pasting, eg. __LINE__. */
 #define ___PASTE(a,b) a##b

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 0147c91fa549e6ab46b68c47b46425b272c37571..874132b26d23dfec9c5c09afd5d61c78cc562e0f 100755 (executable)
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -269,7 +269,8 @@ our $Sparse = qr{
                        __init_refok|
                        __kprobes|
                        __ref|
-                       __rcu
+                       __rcu|
+                       __private
                }x;
 our $InitAttributePrefix = qr{__(?:mem|cpu|dev|net_|)};
 our $InitAttributeData = qr{$InitAttributePrefix(?:initdata\b)};