powerpc/ppc32/tracing: Add stack frame to calls of trace_hardirqs_on/off

32-bit variant of the previous patch for 64-bit:

<<
    When an interrupt occurs in userspace, we can call trace_hardirqs_on/off()
    With one level stack. But if we have irqsoff tracing enabled,
    it checks both CALLER_ADDR0 and CALLER_ADDR1. The second call
    goes two stack frames up. If this is from user space, then there may
    not exist a second stack....
>>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/entry_32.S

@@ -880,7 +880,18 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_47x)
 	 */
 	andi.	r10,r9,MSR_EE
 	beq	1f
+	/*
+	 * Since the ftrace irqsoff latency trace checks CALLER_ADDR1,
+	 * which is the stack frame here, we need to force a stack frame
+	 * in case we came from user space.
+	 */
+	stwu	r1,-32(r1)
+	mflr	r0
+	stw	r0,4(r1)
+	stwu	r1,-32(r1)
 	bl	trace_hardirqs_on
+	lwz	r1,0(r1)
+	lwz	r1,0(r1)
 	lwz	r9,_MSR(r1)
 1:
 #endif /* CONFIG_TRACE_IRQFLAGS */