[RFC][PATCH] Add EXPORT_MACRO_SYMBOL() for asm

[Steven Rostedt]

Commit 784d5699eddc5 ("x86: move exports to actual definitions") removed the
EXPORT_SYMBOL(__fentry__) and EXPORT_SYMBOL(mcount) from x8664_ksyms_64.c,
and added EXPORT_SYMBOL(function_hook) in mcount_64.S instead. The problem
is that function_hook isn't a function at all, but a macro that is defined
as eithe mcount or __fentry__ depending on the support from gcc. But instead
of adding more #ifdefs like x8684_ksyms_64.c had, I suggest having another
export that can handle this similar to the way __string() works with
converting macros to strings. By having:

 EXPORT_MACRO_SYMBOL(function_hook)

Where we have:

 #define EXPORT_MACRO_SYMBOL(x) EXPORT_SYMBOL(x)

It will convert the macro into what it is defined as before calling
EXPORT_SYMBOL(), and this will just work properly again.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: Commit 784d5699eddc5 ("x86: move exports to actual definitions")
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 arch/x86/kernel/mcount_64.S  | 2 +-
 include/asm-generic/export.h | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
index efe73aacf966..ccd9d912af27 100644
--- a/arch/x86/kernel/mcount_64.S
+++ b/arch/x86/kernel/mcount_64.S
@@ -295,7 +295,7 @@ trace:
 	jmp fgraph_trace
 END(function_hook)
 #endif /* CONFIG_DYNAMIC_FTRACE */
-EXPORT_SYMBOL(function_hook)
+EXPORT_MACRO_SYMBOL(function_hook)
 #endif /* CONFIG_FUNCTION_TRACER */
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
index 43199a049da5..cb86e746865e 100644
--- a/include/asm-generic/export.h
+++ b/include/asm-generic/export.h
@@ -90,5 +90,10 @@
 	__EXPORT_SYMBOL(name, KSYM(name),)
 #define EXPORT_DATA_SYMBOL_GPL(name)				\
 	__EXPORT_SYMBOL(name, KSYM(name),_gpl)
+/*
+ * If "name" is a macro of a function and not a function itself,
+ * it needs a second pass.
+ */
+#define EXPORT_MACRO_SYMBOL(x) EXPORT_SYMBOL(x)
 
 #endif
-- 
1.9.3