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Subject[PATCH v4 3/6] riscv/ftrace: Add dynamic function graph tracer support
Date
Once the function_graph tracer is enabled, a filtered function has the
following call sequence:

* ftracer_caller ==> on/off by ftrace_make_call/ftrace_make_nop
* ftrace_graph_caller
* ftrace_graph_call ==> on/off by ftrace_en/disable_ftrace_graph_caller
* prepare_ftrace_return

Considering the following DYNAMIC_FTRACE_WITH_REGS feature, it would be
more extendable to have a ftrace_graph_caller function, instead of
calling prepare_ftrace_return directly in ftrace_caller.

Cc: Greentime Hu <greentime@andestech.com>
Signed-off-by: Alan Kao <alankao@andestech.com>
---
arch/riscv/kernel/ftrace.c | 55 +++++++++++++++++++++++++++++++++++-
arch/riscv/kernel/mcount-dyn.S | 64 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 118 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index be4b24332d97..5bbe1afd9463 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -139,4 +139,57 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
return;
*parent = return_hooker;
}
-#endif
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+extern void ftrace_graph_call(void);
+int ftrace_enable_ftrace_graph_caller(void)
+{
+ unsigned int call[2];
+ static int init_graph = 1;
+ int ret;
+
+ make_call(&ftrace_graph_call, &ftrace_stub, call);
+
+ /*
+ * When enabling graph tracer for the first time, ftrace_graph_call
+ * should contains a call to ftrace_stub. Once it has been disabled,
+ * the 8-bytes at the position becomes NOPs.
+ */
+ if (init_graph) {
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ call);
+ init_graph = 0;
+ } else {
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ NULL);
+ }
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call((unsigned long)&ftrace_graph_call,
+ (unsigned long)&prepare_ftrace_return, true);
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+ unsigned int call[2];
+ int ret;
+
+ make_call(&ftrace_graph_call, &prepare_ftrace_return, call);
+
+ /*
+ * This is to make sure that ftrace_enable_ftrace_graph_caller
+ * did the right thing.
+ */
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ call);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call((unsigned long)&ftrace_graph_call,
+ (unsigned long)&prepare_ftrace_return, false);
+}
+#endif /* CONFIG_DYNAMIC_FTRACE */
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index a3ebeadbe698..739e07a6fd85 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -14,18 +14,62 @@
.text

.macro SAVE_ABI_STATE
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ addi sp, sp, -48
+ sd s0, 32(sp)
+ sd ra, 40(sp)
+ addi s0, sp, 48
+ sd t0, 24(sp)
+ sd t1, 16(sp)
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ sd t2, 8(sp)
+#endif
+#else
addi sp, sp, -16
sd s0, 0(sp)
sd ra, 8(sp)
addi s0, sp, 16
+#endif
.endm

.macro RESTORE_ABI_STATE
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ ld s0, 32(sp)
+ ld ra, 40(sp)
+ addi sp, sp, 48
+#else
ld ra, 8(sp)
ld s0, 0(sp)
addi sp, sp, 16
+#endif
.endm

+ .macro RESTORE_GRAPH_ARGS
+ ld a0, 24(sp)
+ ld a1, 16(sp)
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ ld a2, 8(sp)
+#endif
+ .endm
+
+ENTRY(ftrace_graph_caller)
+ addi sp, sp, -16
+ sd s0, 0(sp)
+ sd ra, 8(sp)
+ addi s0, sp, 16
+ftrace_graph_call:
+ .global ftrace_graph_call
+ /*
+ * Calling ftrace_enable/disable_ftrace_graph_caller would overwrite the
+ * call below. Check ftrace_modify_all_code for details.
+ */
+ call ftrace_stub
+ ld ra, 8(sp)
+ ld s0, 0(sp)
+ addi sp, sp, 16
+ ret
+ENDPROC(ftrace_graph_caller)
+
ENTRY(ftrace_caller)
/*
* a0: the address in the caller when calling ftrace_caller
@@ -33,6 +77,20 @@ ENTRY(ftrace_caller)
*/
ld a1, -8(s0)
addi a0, ra, -MCOUNT_INSN_SIZE
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ /*
+ * the graph tracer (specifically, prepare_ftrace_return) needs these
+ * arguments but for now the function tracer occupies the regs, so we
+ * save them in temporary regs to recover later.
+ */
+ addi t0, s0, -8
+ mv t1, a0
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ ld t2, -16(s0)
+#endif
+#endif
+
SAVE_ABI_STATE
ftrace_call:
.global ftrace_call
@@ -45,6 +103,12 @@ ftrace_call:
* Check ftrace_modify_all_code for details.
*/
call ftrace_stub
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ RESTORE_GRAPH_ARGS
+ call ftrace_graph_caller
+#endif
+
RESTORE_ABI_STATE
ret
ENDPROC(ftrace_caller)
--
2.15.1
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