[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: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 49a6ba926c2b..159d0416f270 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/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 */