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Subject[PATCH] x86: Fix export for mcount and __fentry__
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 either mcount or __fentry__ depending on the support from gcc.

Originally, I thought this was a macro issue, like what __stringify()
is used for. But the problem is a bit deeper. The Makefile.build has
some magic that does post processing of files to create the CRC
bindings. It does some searches for EXPORT_SYMBOL() and because it
finds a macro name and not the actual functions, this causes
function_hook not to be converted into mcount or __fentry__ and they
are missed.

Instead of adding more magic to Makefile.build, just add
EXPORT_SYMBOL() for mcount and __fentry__ where the ifdef is used.
Since this is assembly and not C, it doesn't require being set after
the function is defined.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/kernel/mcount_64.S | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-trace.git/arch/x86/kernel/mcount_64.S
===================================================================
--- linux-trace.git.orig/arch/x86/kernel/mcount_64.S 2016-10-24 11:35:14.410524414 -0400
+++ linux-trace.git/arch/x86/kernel/mcount_64.S 2016-10-24 11:37:23.593443665 -0400
@@ -18,8 +18,10 @@

#ifdef CC_USING_FENTRY
# define function_hook __fentry__
+EXPORT_SYMBOL(__fentry__)
#else
# define function_hook mcount
+EXPORT_SYMBOL(mcount)
#endif

/* All cases save the original rbp (8 bytes) */
@@ -295,7 +297,6 @@ trace:
jmp fgraph_trace
END(function_hook)
#endif /* CONFIG_DYNAMIC_FTRACE */
-EXPORT_SYMBOL(function_hook)
#endif /* CONFIG_FUNCTION_TRACER */

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
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