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Message-ID: <20240603190821.717065217@goodmis.org>
Date: Mon, 03 Jun 2024 15:07:09 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
linux-trace-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>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Florent Revest <revest@...omium.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
bpf <bpf@...r.kernel.org>,
Sven Schnelle <svens@...ux.ibm.com>,
Alexei Starovoitov <ast@...nel.org>,
Jiri Olsa <jolsa@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Alan Maguire <alan.maguire@...cle.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Guo Ren <guoren@...nel.org>
Subject: [PATCH v3 05/27] function_graph: Handle tail calls for stack unwinding
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
For the tail-call, there would be 2 or more ftrace_ret_stacks on the
ret_stack, which records "return_to_handler" as the return address except
for the last one. But on the real stack, there should be 1 entry because
tail-call reuses the return address on the stack and jump to the next
function.
In ftrace_graph_ret_addr() that is used for stack unwinding, skip tail
calls as a real stack unwinder would do.
Link: https://lore.kernel.org/linux-trace-kernel/171509096221.162236.8806372072523195752.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
kernel/trace/fgraph.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index aae51f746828..8de2a2662281 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -594,16 +594,26 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
unsigned long ret, unsigned long *retp)
{
struct ftrace_ret_stack *ret_stack;
+ unsigned long return_handler = (unsigned long)dereference_kernel_function_descriptor(return_to_handler);
int i = task->curr_ret_stack;
- if (ret != (unsigned long)dereference_kernel_function_descriptor(return_to_handler))
+ if (ret != return_handler)
return ret;
while (i > 0) {
ret_stack = get_ret_stack(current, i, &i);
if (!ret_stack)
break;
- if (ret_stack->retp == retp)
+ /*
+ * For the tail-call, there would be 2 or more ftrace_ret_stacks on
+ * the ret_stack, which records "return_to_handler" as the return
+ * address except for the last one.
+ * But on the real stack, there should be 1 entry because tail-call
+ * reuses the return address on the stack and jump to the next function.
+ * Thus we will continue to find real return address.
+ */
+ if (ret_stack->retp == retp &&
+ ret_stack->ret != return_handler)
return ret_stack->ret;
}
@@ -614,10 +624,11 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
unsigned long ret, unsigned long *retp)
{
struct ftrace_ret_stack *ret_stack;
+ unsigned long return_handler = (unsigned long)dereference_kernel_function_descriptor(return_to_handler);
int offset = task->curr_ret_stack;
int i;
- if (ret != (unsigned long)dereference_kernel_function_descriptor(return_to_handler))
+ if (ret != return_handler)
return ret;
if (!idx)
@@ -626,6 +637,8 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
i = *idx;
do {
ret_stack = get_ret_stack(task, offset, &offset);
+ if (ret_stack && ret_stack->ret == return_handler)
+ continue;
i--;
} while (i >= 0 && ret_stack);
--
2.43.0
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