[PATCH 1/3] compiler.h: add ASSERT_STATIC_STORAGE()

[Yury Norov <yury.norov@gmail.com>]

Static lock initializers rely on a persistent object address when lockdep
assigns a lock-class key. Using such an initializer for an automatic local
object can compile successfully but disable lockdep on the first lock
acquisition.

Add ASSERT_STATIC_STORAGE() for declaration macros that require
static storage duration. It declares an unused static pointer initialized
with the object's address. An automatic local object's address is not a
valid static initializer, so the compiler rejects it.

Mirror the helper in tools/include/linux/compiler.h because the userspace
radix-tree tests include the kernel IDA and Maple Tree headers with the
tools compiler definitions.

For example:

  void example(void)
  {
          int object;
          ASSERT_STATIC_STORAGE(object);
  }

GCC reports:

  error: initializer element is not constant
    name##_storage_check = &(name)
                           ^
  note: in expansion of macro 'ASSERT_STATIC_STORAGE'
    ASSERT_STATIC_STORAGE(object);

File-scope objects and static local objects remain valid. The helper takes
an object identifier and must be used as a declaration after that object
has been declared.

Link: https://lore.kernel.org/all/20260911155244.1406122-1-ynorov@nvidia.com/
Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
 include/linux/compiler.h       | 5 +++++
 tools/include/linux/compiler.h | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index cb2f6050bdf7..ef9036fa5413 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -275,6 +275,11 @@ static inline void *offset_to_ptr(const int *off)
 #define __ADDRESSABLE(sym) \
 	___ADDRESSABLE(sym, __section(".discard.addressable"))
 
+/* Enforce static storage duration. */
+#define ASSERT_STATIC_STORAGE(name) \
+	static typeof(name) * const __always_unused \
+		name##_storage_check = &(name)
+
 /*
  * This returns a constant expression while determining if an argument is
  * a constant expression, most importantly without evaluating the argument.
diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
index f2f54b038168..03ecf9086643 100644
--- a/tools/include/linux/compiler.h
+++ b/tools/include/linux/compiler.h
@@ -73,6 +73,11 @@
 # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 #endif
 
+/* Enforce static storage duration. */
+#define ASSERT_STATIC_STORAGE(name) \
+	static typeof(name) * const __always_unused \
+		name##_storage_check = &(name)
+
 /*
  * This returns a constant expression while determining if an argument is
  * a constant expression, most importantly without evaluating the argument.
-- 
2.53.0