[ARM] 5418/1: restore lr before leaving mcount

gcc seems to expect that lr isn't clobbered by mcount, because for a
function starting with:

	static int func(void)
	{
		void *ra = __builtin_return_address(0);

		printk(KERN_EMERG "__builtin_return_address(0) = %pS\n", ra)

		...

the following assembler is generated by gcc 4.3.2:

	   0:   e1a0c00d        mov     ip, sp
	   4:   e92dd810        push    {r4, fp, ip, lr, pc}
	   8:   e24cb004        sub     fp, ip, #4      ; 0x4
	   c:   ebfffffe        bl      0 <mcount>
	  10:   e59f0034        ldr     r0, [pc, #52]
	  14:   e1a0100e        mov     r1, lr
	  18:   ebfffffe        bl      0 <printk>

Without this patch obviously __builtin_return_address(0) yields
func+0x10 instead of the return address of the caller.

Note this patch fixes a similar issue for the routines used with dynamic
ftrace even though this isn't currently selectable for ARM.

Cc: Abhishek Sagar <sagar.abhishek@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/entry-common.S

@@ -111,6 +111,7 @@ ENTRY(mcount)
 	.globl mcount_call
 mcount_call:
 	bl ftrace_stub
+	ldr lr, [fp, #-4]			@ restore lr
 	ldmia sp!, {r0-r3, pc}
 
 ENTRY(ftrace_caller)
@@ -122,6 +123,7 @@ ENTRY(ftrace_caller)
 	.globl ftrace_call
 ftrace_call:
 	bl ftrace_stub
+	ldr lr, [fp, #-4]			@ restore lr
 	ldmia sp!, {r0-r3, pc}
 
 #else
@@ -133,6 +135,7 @@ ENTRY(mcount)
 	adr r0, ftrace_stub
 	cmp r0, r2
 	bne trace
+	ldr lr, [fp, #-4]			@ restore lr
 	ldmia sp!, {r0-r3, pc}
 
 trace:
@@ -141,6 +144,7 @@ trace:
 	sub r0, r0, #MCOUNT_INSN_SIZE
 	mov lr, pc
 	mov pc, r2
+	mov lr, r1				@ restore lr
 	ldmia sp!, {r0-r3, pc}
 
 #endif /* CONFIG_DYNAMIC_FTRACE */