linux-kernel - [for-linus][PATCH 3/3] ftrace/microblaze: Do not find "true

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Message-ID: <20241213152704.448212590@goodmis.org>
Date: Fri, 13 Dec 2024 10:26:50 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Al Viro <viro@...IV.linux.org.uk>,
 Michal Simek <monstr@...str.eu>,
 Al Viro <viro@...iv.linux.org.uk>
Subject: [for-linus][PATCH 3/3] ftrace/microblaze: Do not find "true_parent" for return address

From: Steven Rostedt <rostedt@...dmis.org>

When function tracing and function graph tracing are both enabled (in
different instances) the "parent" of some of the function tracing events
is "return_to_handler" which is the trampoline used by function graph
tracing. To fix this, ftrace_get_true_parent_ip() was introduced that
returns the "true" parent ip instead of the trampoline.

To do this, the ftrace_regs_get_stack_pointer() is used, which uses
kernel_stack_pointer(). The problem is that microblaze does not implement
kerenl_stack_pointer() so when function graph tracing is enabled, the
build fails.

Modify the #ifdef check to the code around ftrace_get_true_parent_ip() to
include !defined(CONFIG_MICROBLAZE) which will default it to just return
the parent ip passed in, which may still be the ip of the function garph
trampoline.

Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Al Viro <viro@...IV.linux.org.uk>
Cc: Michal Simek <monstr@...str.eu>
Link: https://lore.kernel.org/20241211153634.69c75afa@batman.local.home
Fixes: 60b1f578b578 ("ftrace: Get the true parent ip for function tracer")
Reported-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_functions.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 74c353164ca1..a75d107a45f8 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -176,7 +176,8 @@ static void function_trace_start(struct trace_array *tr)
 	tracing_reset_online_cpus(&tr->array_buffer);
 }

-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+/* Microblaze currently doesn't implement kernel_stack_pointer() */
+#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && !defined(CONFIG_MICROBLAZE)
 static __always_inline unsigned long
 function_get_true_parent_ip(unsigned long parent_ip, struct ftrace_regs *fregs)
 {
-- 
2.45.2