[PATCH v4 04/10] mm/kasan: define __asan_before_dynamic_init, __asan_after_dynamic_init

[Alexander Potapenko <glider@google.com>]

Calls to __asan_before_dynamic_init() and __asan_after_dynamic_init()
are inserted by Clang when building with coverage guards.
These functions can be used to detect initialization order fiasco bugs
in the userspace, but it is fine for them to be no-ops in the kernel.

Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

---
v4:
 - Fix a compilation error reported by the kernel test robot <lkp@intel.com>

v3:
 - add Reviewed-by: Dmitry Vyukov

v2:
 - Address comments by Dmitry Vyukov:
   - rename CONFIG_KCOV_ENABLE_GUARDS to CONFIG_KCOV_UNIQUE
 - Move this patch before the one introducing CONFIG_KCOV_UNIQUE,
   per Marco Elver's request.

Change-Id: I7f8eb690a3d96f7d122205e8f1cba8039f6a68eb

fixup asan_before

Change-Id: If653ba4f160414cafe65eee530b6b67e5b5b547c
---
 mm/kasan/generic.c | 24 ++++++++++++++++++++++++
 mm/kasan/kasan.h   |  2 ++
 2 files changed, 26 insertions(+)

diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index d54e89f8c3e76..b43ac17b7c926 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -238,6 +238,30 @@ void __asan_unregister_globals(void *ptr, ssize_t size)
 }
 EXPORT_SYMBOL(__asan_unregister_globals);
 
+#if defined(CONFIG_KCOV_UNIQUE)
+/*
+ * __asan_before_dynamic_init() and __asan_after_dynamic_init() are inserted
+ * when the user requests building with coverage guards. In the userspace, these
+ * two functions can be used to detect initialization order fiasco bugs, but in
+ * the kernel they can be no-ops.
+ *
+ * There is an inconsistency between how Clang and GCC emit calls to this
+ * function, with Clang expecting the parameter to be i64, whereas GCC wants it
+ * to be const void *.
+ * We pick the latter option, because Clang does not care, and GCC prints a
+ * warning with -Wbuiltin-declaration-mismatch.
+ */
+void __asan_before_dynamic_init(const void *module_name)
+{
+}
+EXPORT_SYMBOL(__asan_before_dynamic_init);
+
+void __asan_after_dynamic_init(void)
+{
+}
+EXPORT_SYMBOL(__asan_after_dynamic_init);
+#endif
+
 #define DEFINE_ASAN_LOAD_STORE(size)					\
 	void __asan_load##size(void *addr)				\
 	{								\
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 129178be5e649..d23fcac9e0c12 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -582,6 +582,8 @@ void kasan_restore_multi_shot(bool enabled);
 
 void __asan_register_globals(void *globals, ssize_t size);
 void __asan_unregister_globals(void *globals, ssize_t size);
+void __asan_before_dynamic_init(const void *module_name);
+void __asan_after_dynamic_init(void);
 void __asan_handle_no_return(void);
 void __asan_alloca_poison(void *, ssize_t size);
 void __asan_allocas_unpoison(void *stack_top, ssize_t stack_bottom);
-- 
2.50.1.552.g942d659e1b-goog