linux-kernel - [RFC PATCH 3/6] powerpc: Indicate traced function name in show

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Message-Id: <9358c81e47f9d395d90691f77f50feaf20be963e.1621577151.git.naveen.n.rao@linux.vnet.ibm.com>
Date:   Fri, 21 May 2021 12:18:38 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Suchanek <msuchanek@...e.de>,
        Torsten Duwe <duwe@...e.de>
Cc:     <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 3/6] powerpc: Indicate traced function name in show_stack()

With -mprofile-kernel and ppc32, the function tracer is invoked before a
function sets up its own stackframe. This results in the traced function
not appearing in stack traces. Fix this by checking for ftrace entry and
including the traced function in the stack trace.

With this patch, stack traces show the function traced next to the
ftrace entry:
    NIP [c0080000003700d4] handler_pre+0x1c/0x5c [kprobe_example]
    LR [c00000000006c118] kprobe_ftrace_handler+0x1b8/0x270
    Call Trace:
    [c00000001ed7fa50] [c00000001ed7faa0] 0xc00000001ed7faa0 (unreliable)
    [c00000001ed7fab0] [c00000000006c118] kprobe_ftrace_handler+0x1b8/0x270
    [c00000001ed7fb00] [c000000000076604] ftrace_regs_call+0x4/0xa4 (kernel_clone+0xc/0x600)
                                                                    ^^^^^^^^^^^^^^^^^^^^^^^^
    [c00000001ed7fcf0] [c000000000139e08] __do_sys_clone+0x88/0xd0
    [c00000001ed7fdb0] [c00000000002b6c4] system_call_exception+0xf4/0x200
    [c00000001ed7fe10] [c00000000000ca5c] system_call_common+0xec/0x278

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/process.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 89e34aa273e21a..9df1d44939bec1 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2160,6 +2160,9 @@ void show_stack(struct task_struct *tsk, unsigned long *stack,
 						&ftrace_idx, ip, stack);
 			if (ret_addr != ip)
 				pr_cont(" (%pS)", (void *)ret_addr);
+			ip = ftrace_get_traced_func_if_no_stackframe(ip, stack);
+			if (ip)
+				pr_cont(" (%pS)", (void *)ip);
 			if (firstframe)
 				pr_cont(" (unreliable)");
 			pr_cont("\n");
-- 
2.30.2