[PATCH -next 6/7] riscv: stacktrace: Fix unwinding on ftrace_regs_call

[Chen Zhongjin]

When unwinding on ftrace_regs_call, the traced function will be skipped
because ftrace_regs_caller doesn't save the fp and ra.

Save the encoded fp so that we can get the pt_regs so that we can unwind
from ftrace_regs_call to the traced function.

Also the pt_regs->status should be set as kernel mode.

Stacktrace before this patch:

 Call Trace:
  ...
  [<ffffffff0161a0e0>] handler_pre+0x30/0x4a [kprobe_unwind]
  [<ffffffff800bce92>] aggr_pre_handler+0x60/0x94
  [<ffffffff80006df0>] kprobe_ftrace_handler+0x13e/0x188
  [<ffffffff80008e7e>] ftrace_regs_call+0x8/0x10
  [<ffffffff80002540>] do_one_initcall+0x4c/0x1f2
  [<ffffffff8008a4e6>] do_init_module+0x56/0x210
 ...

Stacktrace after this patch:

 Call Trace:
  ...
  [<ffffffff016150e0>] handler_pre+0x30/0x4a [kprobe_unwind]
  [<ffffffff800bce96>] aggr_pre_handler+0x60/0x94
  [<ffffffff80006df0>] kprobe_ftrace_handler+0x13e/0x188
  [<ffffffff80008e82>] ftrace_regs_call+0x8/0x10
+ [<ffffffff01615000>] empty_call+0x0/0x1e [kprobe_unwind]
  [<ffffffff80002540>] do_one_initcall+0x4c/0x1f2
  [<ffffffff8008a4ea>] do_init_module+0x56/0x210
  ...

Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
---
 arch/riscv/kernel/mcount-dyn.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index d171eca623b6..56a4014c392f 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -10,6 +10,8 @@
 #include <asm/asm-offsets.h>
 #include <asm-generic/export.h>
 #include <asm/ftrace.h>
+#include <asm/frame.h>
+#include <asm/csr.h>
 
 	.text
 
@@ -97,6 +99,11 @@
 	REG_S x29, PT_T4(sp)
 	REG_S x30, PT_T5(sp)
 	REG_S x31, PT_T6(sp)
+
+#ifdef CONFIG_FRAME_POINTER
+	li s0, SR_PP
+	REG_S s0, PT_STATUS(sp)
+#endif
 	.endm
 
 	.macro RESTORE_ALL
@@ -172,6 +179,7 @@ ENDPROC(ftrace_caller)
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 ENTRY(ftrace_regs_caller)
 	SAVE_ALL
+	ENCODE_FRAME_POINTER
 
 	addi	a0, ra, -FENTRY_RA_OFFSET
 	la	a1, function_trace_op
-- 
2.17.1