static_call: Provide DEFINE_STATIC_CALL_RET0()

DECLARE_STATIC_CALL() must pass the original function targeted for a
given static call. But DEFINE_STATIC_CALL() may want to initialize it as
off. In this case we can't pass NULL (for functions without return value)
or __static_call_return0 (for functions returning a value) directly
to DEFINE_STATIC_CALL() as that may trigger a static call redeclaration
with a different function prototype. Type casts neither can work around
that as they don't get along with typeof().

The proper way to do that for functions that don't return a value is
to use DEFINE_STATIC_CALL_NULL(). But functions returning a actual value
don't have an equivalent yet.

Provide DEFINE_STATIC_CALL_RET0() to solve this situation.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210118141223.123667-3-frederic@kernel.org

diff --git a/include/linux/static_call.h b/include/linux/static_call.h
index bd6735d..d69dd8b 100644 (file)
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -144,13 +144,13 @@ extern int static_call_text_reserved(void *start, void *end);
 
 extern long __static_call_return0(void);
 
-#define DEFINE_STATIC_CALL(name, _func)                                        \
+#define __DEFINE_STATIC_CALL(name, _func, _func_init)                  \
        DECLARE_STATIC_CALL(name, _func);                               \
        struct static_call_key STATIC_CALL_KEY(name) = {                \
-               .func = _func,                                          \
+               .func = _func_init,                                     \
                .type = 1,                                              \
        };                                                              \
-       ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
+       ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func_init)
 
 #define DEFINE_STATIC_CALL_NULL(name, _func)                           \
        DECLARE_STATIC_CALL(name, _func);                               \
@@ -178,12 +178,12 @@ struct static_call_key {
        void *func;
 };
 
-#define DEFINE_STATIC_CALL(name, _func)                                        \
+#define __DEFINE_STATIC_CALL(name, _func, _func_init)                  \
        DECLARE_STATIC_CALL(name, _func);                               \
        struct static_call_key STATIC_CALL_KEY(name) = {                \
-               .func = _func,                                          \
+               .func = _func_init,                                     \
        };                                                              \
-       ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func)
+       ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func_init)
 
 #define DEFINE_STATIC_CALL_NULL(name, _func)                           \
        DECLARE_STATIC_CALL(name, _func);                               \
@@ -234,10 +234,10 @@ static inline long __static_call_return0(void)
        return 0;
 }
 
-#define DEFINE_STATIC_CALL(name, _func)                                        \
+#define __DEFINE_STATIC_CALL(name, _func, _func_init)                  \
        DECLARE_STATIC_CALL(name, _func);                               \
        struct static_call_key STATIC_CALL_KEY(name) = {                \
-               .func = _func,                                          \
+               .func = _func_init,                                     \
        }
 
 #define DEFINE_STATIC_CALL_NULL(name, _func)                           \
@@ -286,4 +286,10 @@ static inline int static_call_text_reserved(void *start, void *end)
 
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
+#define DEFINE_STATIC_CALL(name, _func)                                        \
+       __DEFINE_STATIC_CALL(name, _func, _func)
+
+#define DEFINE_STATIC_CALL_RET0(name, _func)                           \
+       __DEFINE_STATIC_CALL(name, _func, __static_call_return0)
+
 #endif /* _LINUX_STATIC_CALL_H */