[PATCH] Make Function Duration Tracer work with __gnu_mcount_nc

[Ashwin Chaugule <ashwinc@codeaurora.org>]

Is there a better way to fix this in the original ftrace_graph_caller ?
The lr isn't pushed on the stack before "bl mcount".

--

From: Ashwin Chaugule <ashwinc@quicinc.com>

Newer compilers use the __gnu_mcount_nc stub in every function
prologue. The lr of the instrumented function is pushed on the
stack before branching to __gnu_mcount_nc. Pop it before returning
back to instrumented function so that it can return to its parent
from its epilogue.


Signed-off-by: Ashwin Chaugule <ashwinc@quicinc.com>
---
 arch/arm/kernel/entry-common.S |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index b8a9e47..30feac3 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -144,6 +144,14 @@ ENTRY(__gnu_mcount_nc)
     adr r0, ftrace_stub
     cmp r0, r2
     bne gnu_trace
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+    ldr r1, =ftrace_graph_return
+    ldr r2, [r1]
+    cmp r0, r2        @ if *ftrace_graph_return != ftrace_stub
+    bne new_ftrace_graph_caller
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
     ldmia sp!, {r0-r3, ip, lr}
     bx ip
 
@@ -155,6 +163,18 @@ gnu_trace:
     mov pc, r2
     ldmia sp!, {r0-r3, ip, lr}
     bx ip
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ENTRY(new_ftrace_graph_caller)        @ for use with __gnu_mcount_nc
+    sub r0, fp, #4                    @ &lr of instrumented routine 
(&parent)
+    mov r1, lr                        @ instrumented routine (func)
+    sub r1, r1, #MCOUNT_INSN_SIZE
+    mov r2, fp                        @ frame pointer
+    bl prepare_ftrace_return
+    ldmia sp!, {r0-r3, ip, lr}        @ need to pop lr, pushed before
+    mov pc, ip                        @ bl __gnu_mcount_nc
+
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
    
 ENTRY(mcount)
     stmdb sp!, {r0-r3, lr}
-- 
1.5.6.3