[PATCH v5 3/4] cleanup: Annotate guard constructors with nonnull

[Dmitry Ilvokhin <d@ilvokhin.com>]

Add __nonnull_args() to unconditional guard constructors so the compiler
warns when NULL is statically known to be passed:

- DEFINE_GUARD(): re-declare the constructor with __nonnull_args().
- __DEFINE_LOCK_GUARD_1(): annotate the constructor directly.

DEFINE_LOCK_GUARD_0() needs no annotation: its constructor takes no
pointer arguments (.lock is hardcoded to (void *)1).

Define the __nonnull_args() macro in compiler_attributes.h, following
the existing convention for attribute wrappers. Deliberately not named
'__nonnull', to avoid clashing with glibc's __nonnull() when kernel and
userspace headers are combined (User Mode Linux for example).

Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
---
Miguel, I dropped your Acked-by due to the rename. Went with
__nonnull_args() (over __knonnull()). Happy to restore your tag if that
spelling works for you.

 include/linux/cleanup.h             | 4 +++-
 include/linux/compiler_attributes.h | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index ea95ca4bc11c..4e60d519713c 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -397,6 +397,7 @@ static __maybe_unused const bool class_##_name##_is_conditional = _is_cond
 	__DEFINE_GUARD_LOCK_PTR(_name, _T)
 
 #define DEFINE_GUARD(_name, _type, _lock, _unlock) \
+	static __always_inline __nonnull_args() _type class_##_name##_constructor(_type _T); \
 	DEFINE_CLASS(_name, _type, if (_T) { _unlock; }, ({ _lock; _T; }), _type _T); \
 	DEFINE_CLASS_IS_GUARD(_name)
 
@@ -497,7 +498,8 @@ static __always_inline void class_##_name##_destructor(class_##_name##_t *_T) \
 __DEFINE_GUARD_LOCK_PTR(_name, &_T->lock)
 
 #define __DEFINE_LOCK_GUARD_1(_name, _type, ...)			\
-static __always_inline class_##_name##_t class_##_name##_constructor(_type *l) \
+static __always_inline __nonnull_args()					\
+class_##_name##_t class_##_name##_constructor(_type *l)			\
 	__no_context_analysis						\
 {									\
 	class_##_name##_t _t = { .lock = l }, *_T = &_t;		\
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index c16d4199bf92..cffe09387ea6 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -230,6 +230,15 @@
  */
 #define   noinline                      __attribute__((__noinline__))
 
+/*
+ * Note: deliberately not named '__nonnull', to avoid clashing with glibc's
+ * __nonnull() when kernel and userspace headers are combined.
+ *
+ *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Attributes.html#index-nonnull
+ * clang: https://clang.llvm.org/docs/AttributeReference.html#nonnull
+ */
+#define __nonnull_args(x...)		__attribute__((__nonnull__(x)))
+
 /*
  * Optional: only supported since gcc >= 8
  * Optional: not supported by clang
-- 
2.53.0-Meta