ARM: 7440/1: kprobes: only test 'sub pc, pc, #1b-2b+8-2' on ARMv6
Rabin Vincent [Wed, 4 Jul 2012 06:37:37 +0000 (07:37 +0100)]
'sub pc, pc, #1b-2b+8-2' results in address<1:0> == '10'.

sub pc, pc, #const (== ADR pc, #const) performs an interworking branch
(BXWritePC()) on ARMv7+ and a simple branch (BranchWritePC()) on earlier
versions.

In ARM state, BXWritePC() is UNPREDICTABLE when address<1:0> == '10'.

In ARM state on ARMv6+, BranchWritePC() ignores address<1:0>.  Before
ARMv6, BranchWritePC() is UNPREDICTABLE if address<1:0> != '00'

So the instruction is UNPREDICTABLE both before and after v6.

Acked-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/kprobes-test-arm.c

index ba32b39..38c1a3b 100644 (file)
@@ -187,8 +187,8 @@ void kprobe_arm_test_cases(void)
        TEST_BF_R ("mov pc, r",0,2f,"")
        TEST_BF_RR("mov pc, r",0,2f,", asl r",1,0,"")
        TEST_BB(   "sub pc, pc, #1b-2b+8")
-#if __LINUX_ARM_ARCH__ >= 6
-       TEST_BB(   "sub pc, pc, #1b-2b+8-2") /* UNPREDICTABLE before ARMv6 */
+#if __LINUX_ARM_ARCH__ == 6 && !defined(CONFIG_CPU_V7)
+       TEST_BB(   "sub pc, pc, #1b-2b+8-2") /* UNPREDICTABLE before and after ARMv6 */
 #endif
        TEST_BB_R( "sub pc, pc, r",14, 1f-2f+8,"")
        TEST_BB_R( "rsb pc, r",14,1f-2f+8,", pc")