Make Function Duration Tracer work with __gnu_mcount_nc

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 <[email protected]>

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 <[email protected]>

---
 arch/arm/kernel/entry-common.S |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

arch/arm/kernel/entry-common.S +20 -0

index b8a9e47..30feac3 100644
@@ -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}

Quoted 57 lines · Ashwin Chaugule

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 <[email protected]>

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 <[email protected]>

---
 arch/arm/kernel/entry-common.S |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

arch/arm/kernel/entry-common.S +20 -0

index b8a9e47..30feac3 100644
@@ -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)

Quoted 2 lines

     stmdb sp!, {r0-r3, lr}

Wow, interesting timing. I just finished yesterday my own version of this patch (for 2.6.29) - it looks amazingingly similar.

What's up with putting fp in r2 - is that required in the latest prepare_ftrace_return()?
-- Tim

------------- patch follows ----------------
Add support to __gnu_mcount_nc, used by newer (4.x?) Gnu compilers, for ftrace function_graph support on ARM.

Signed-off-by Tim Bird <[email protected]>

---
 arch/arm/kernel/entry-common.S |   13 +++++++++++++
 1 file changed, 13 insertions(+)

arch/arm/kernel/entry-common.S +13 -0

@@ -140,6 +140,12 @@ 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 gnu_ftrace_graph_caller
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 	ldmia sp!, {r0-r3, ip, lr}
 	bx ip
 

@@ -196,6 +202,13 @@ return_to_handler:
 	ldmia sp!, {r0-r3}
 	mov pc, lr
 
+ENTRY(gnu_ftrace_graph_caller)
+	sub r0, fp, #4			@ &lr of instrumented routine (&parent)
+	sub r1, lr, #MCOUNT_INSN_SIZE	@ instrumented routine (func)
+	bl prepare_ftrace_return
+	ldmia sp!, {r0-r3, ip, lr}
+	bx ip
+
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
 #endif /* CONFIG_DYNAMIC_FTRACE */