riscv/stacktrace: Fix stack output without ra on the stack top

When a function doesn't have a callee, then it will not
push ra into the stack, such as lkdtm_BUG() function,

addi	sp,sp,-16
sd	s0,8(sp)
addi	s0,sp,16
ebreak

The struct stackframe use {fp,ra} to get information from
stack, if walk_stackframe() with pr_regs, we will obtain
wrong value and bad stacktrace,

[<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
---[ end trace 18da3fbdf08e25d5 ]---

Correct the next fp and pc, after that, full stacktrace
shown as expects,

[<ffffffe00066c56c>] lkdtm_BUG+0x6/0x8
[<ffffffe0008b24a4>] lkdtm_do_action+0x14/0x1c
[<ffffffe00066c372>] direct_entry+0xc0/0x10a
[<ffffffe000439f86>] full_proxy_write+0x42/0x6a
[<ffffffe000309626>] vfs_write+0x7e/0x214
[<ffffffe00030992a>] ksys_write+0x98/0xc0
[<ffffffe000309960>] sys_write+0xe/0x16
[<ffffffe0002014bc>] ret_from_syscall+0x0/0x2
---[ end trace 61917f3d9a9fadcd ]---

Signed-off-by: Chen Huang <chenhuang5@huawei.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 76dadf6d396bf4a8ead435df348f36376126b910..51ce3620ac1f6cae7d06545938e9be34a2f87ec9 100644 (file)
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -54,9 +54,15 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
                /* Unwind stack frame */
                frame = (struct stackframe *)fp - 1;
                sp = fp;
-               fp = frame->fp;
-               pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
-                                          (unsigned long *)(fp - 8));
+               if (regs && (regs->epc == pc) && (frame->fp & 0x7)) {
+                       fp = frame->ra;
+                       pc = regs->ra;
+               } else {
+                       fp = frame->fp;
+                       pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
+                                                  (unsigned long *)(fp - 8));
+               }
+
        }
 }