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Date: Wed,  3 Aug 2016 14:59:31 +1000
From: Michael Ellerman <>
To: Kees Cook <>
Cc: <>,
	Andrew Morton <>,
	Greg Kroah-Hartman <>,,
	Anton Blanchard <>,
	Nick Piggin <>
Subject: [PATCH] lkdtm: Mark lkdtm_rodata_do_nothing() notrace

lkdtm_rodata_do_nothing() is an empty function which is generated in
order to test the non-executability of rodata.

Currently if function tracing is enabled then an mcount callsite will be
generated for lkdtm_rodata_do_nothing(), and it will appear in the list
of available functions for function tracing (available_filter_functions).

Given it's purpose purely as a test function, it seems preferable for
lkdtm_rodata_do_nothing() to be marked notrace, so it doesn't appear as

This also avoids triggering a linker bug on powerpc:

When the linker sees code that needs to generate a call stub, eg. a
branch to mcount(), it assumes the section is executable and
dereferences a NULL pointer leading to a linker segfault. Marking
lkdtm_rodata_do_nothing() notrace avoids triggering the bug because the
function contains no other function calls.

Signed-off-by: Michael Ellerman <>
 drivers/misc/lkdtm_rodata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/lkdtm_rodata.c b/drivers/misc/lkdtm_rodata.c
index 166b1db3969f..3564477b8c2d 100644
--- a/drivers/misc/lkdtm_rodata.c
+++ b/drivers/misc/lkdtm_rodata.c
@@ -4,7 +4,7 @@
 #include "lkdtm.h"
-void lkdtm_rodata_do_nothing(void)
+void notrace lkdtm_rodata_do_nothing(void)
 	/* Does nothing. We just want an architecture agnostic "return". */

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