[RFC PATCH 1/1] powerpc/ftrace: Exclude real mode code from

Naveen N. Rao naveen.n.rao at linux.vnet.ibm.com
Thu Mar 8 03:46:19 AEDT 2018

We can't take a trap in most parts of real mode code. Instead of adding
the 'notrace' annotation to all C functions that can be invoked from
real mode, detect that we are in real mode on ftrace entry and return

Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
This RFC only handles -mprofile-kernel to demonstrate the approach being 
considered. We will need to handle other ftrace entry if we decide to 
continue down this path.

- Naveen

 arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index 3f3e81852422..ecc0e8e38ead 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
@@ -56,6 +56,21 @@ _GLOBAL(ftrace_caller)
 	/* Load special regs for save below */
 	mfmsr   r8
+	/* Only proceed if we are not in real mode and can take interrupts */
+	andi.	r9, r8, MSR_IR|MSR_DR|MSR_RI
+	cmpdi	r9, MSR_IR|MSR_DR|MSR_RI
+	beq	1f
+	mflr	r8
+	mtctr	r8
+	REST_GPR(9, r1)
+	REST_GPR(8, r1)
+	addi	r1, r1, SWITCH_FRAME_SIZE
+	ld	r0, LRSAVE(r1)
+	mtlr	r0
+	bctr
 	mfctr   r9
 	mfxer   r10
 	mfcr	r11

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