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x86: Fix export for mcount and __fentry__

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Commit 784d5699ed ("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 <[email protected]>
Tested-by: Borislav Petkov <[email protected]>
Cc: Gabriel C <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Al Viro <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>
This commit is contained in:
Steven Rostedt 2016-10-24 15:01:48 -04:00 • committed by Thomas Gleixner
commit 5de0a8c0c2
1 changed files with 2 additions and 1 deletions
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3
arch/x86/kernel/mcount_64.S
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@ -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