2017-03-15 18:08:33

by Abel Vesa

Subject: [PATCH] arm: ftrace: fix dynamic ftrace with DEBUG_RODATA and !FRAME_POINTER

The support for dynamic ftrace with CONFIG_DEBUG_RODATA involves
overriding the weak arch_ftrace_update_code() with a variant which makes
the kernel text writable around the patching.

This override was however added under the CONFIG_OLD_MCOUNT ifdef, and
CONFIG_OLD_MCOUNT is only enabled if frame pointers are enabled.

This leads to non-functional dynamic ftrace (ftrace triggers a
WARN_ON()) when CONFIG_DEBUG_RODATA is enabled and CONFIG_FRAME_POINTER
is not.

Move the override out of that ifdef and into the CONFIG_DYNAMIC_FTRACE
ifdef where it belongs.

Fixes: 80d6b0c2eed2a ("ARM: mm: allow text and rodata sections to be read-only")

Suggested-by: Nicolai Stange <[email protected]>
Suggested-by: Rabin Vincent <[email protected]>
Signed-off-by: Abel Vesa <[email protected]>
---
arch/arm/kernel/ftrace.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 3f17594..414e60e 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -29,11 +29,6 @@
#endif

#ifdef CONFIG_DYNAMIC_FTRACE
-#ifdef CONFIG_OLD_MCOUNT
-#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
-#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
-
-#define OLD_NOP 0xe1a00000 /* mov r0, r0 */

static int __ftrace_modify_code(void *data)
{
@@ -51,6 +46,12 @@ void arch_ftrace_update_code(int command)
stop_machine(__ftrace_modify_code, &command, NULL);
}

+#ifdef CONFIG_OLD_MCOUNT
+#define OLD_MCOUNT_ADDR ((unsigned long) mcount)
+#define OLD_FTRACE_ADDR ((unsigned long) ftrace_caller_old)
+
+#define OLD_NOP 0xe1a00000 /* mov r0, r0 */
+
static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
{
return rec->arch.old_mcount ? OLD_NOP : NOP;
--
2.7.4

2017-03-18 18:33:52

by Rabin Vincent

Subject: Re: [PATCH] arm: ftrace: fix dynamic ftrace with DEBUG_RODATA and !FRAME_POINTER

On Wed, Mar 15, 2017 at 06:07:39PM +0000, Abel Vesa wrote:
> The support for dynamic ftrace with CONFIG_DEBUG_RODATA involves
> overriding the weak arch_ftrace_update_code() with a variant which makes
> the kernel text writable around the patching.
>
> This override was however added under the CONFIG_OLD_MCOUNT ifdef, and
> CONFIG_OLD_MCOUNT is only enabled if frame pointers are enabled.
>
> This leads to non-functional dynamic ftrace (ftrace triggers a
> WARN_ON()) when CONFIG_DEBUG_RODATA is enabled and CONFIG_FRAME_POINTER
> is not.
>
> Move the override out of that ifdef and into the CONFIG_DYNAMIC_FTRACE
> ifdef where it belongs.
>
> Fixes: 80d6b0c2eed2a ("ARM: mm: allow text and rodata sections to be read-only")
>
> Suggested-by: Nicolai Stange <[email protected]>
> Suggested-by: Rabin Vincent <[email protected]>
> Signed-off-by: Abel Vesa <[email protected]>

Acked-by: Rabin Vincent <[email protected]>