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....@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 
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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