ARM: 6318/1: ftrace: fix and update dynamic ftrace

This adds mcount recording and updates dynamic ftrace for ARM to work
with the new ftrace dyamic tracing implementation.  It also adds support
for the mcount format used by newer ARM compilers.

With dynamic tracing, mcount() is implemented as a nop.  Callsites are
patched on startup with nops, and dynamically patched to call to the
ftrace_caller() routine as needed.

Acked-by: Steven Rostedt <rostedt@goodmis.org> [recordmcount.pl change]
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 28 insertions, 9 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index f5e75de0203e..e02790f28879 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -127,6 +127,10 @@ ENDPROC(ret_from_fork)
  * clobber the ip register.  This is OK because the ARM calling convention
  * allows it to be clobbered in subroutines and doesn't use it to hold
  * parameters.)
+ *
+ * When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0"
+ * for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see
+ * arch/arm/kernel/ftrace.c).
  */
 
 #ifndef CONFIG_OLD_MCOUNT
@@ -136,30 +140,45 @@ ENDPROC(ret_from_fork)
 #endif
 
 #ifdef CONFIG_DYNAMIC_FTRACE
-ENTRY(mcount)
+ENTRY(__gnu_mcount_nc)
+        mov     ip, lr
+        ldmia   sp!, {lr}
+        mov     pc, ip
+ENDPROC(__gnu_mcount_nc)
+
+ENTRY(ftrace_caller)
         stmdb   sp!, {r0-r3, lr}
         mov     r0, lr
         sub     r0, r0, #MCOUNT_INSN_SIZE
+        ldr     r1, [sp, #20]
 
-        .globl mcount_call
-mcount_call:
+        .global ftrace_call
+ftrace_call:
         bl      ftrace_stub
-        ldr     lr, [fp, #-4]                   @ restore lr
-        ldmia   sp!, {r0-r3, pc}
+        ldmia   sp!, {r0-r3, ip, lr}
+        mov     pc, ip
+ENDPROC(ftrace_caller)
+
+#ifdef CONFIG_OLD_MCOUNT
+ENTRY(mcount)
+        stmdb   sp!, {lr}
+        ldr     lr, [fp, #-4]
+        ldmia   sp!, {pc}
 ENDPROC(mcount)
 
-ENTRY(ftrace_caller)
+ENTRY(ftrace_caller_old)
         stmdb   sp!, {r0-r3, lr}
         ldr     r1, [fp, #-4]
         mov     r0, lr
         sub     r0, r0, #MCOUNT_INSN_SIZE
 
-        .globl ftrace_call
-ftrace_call:
+        .globl ftrace_call_old
+ftrace_call_old:
         bl      ftrace_stub
         ldr     lr, [fp, #-4]                   @ restore lr
         ldmia   sp!, {r0-r3, pc}
-ENDPROC(ftrace_caller)
+ENDPROC(ftrace_caller_old)
+#endif
 
 #else