Commit 375bb572 authored by Masami Hiramatsu (Google)'s avatar Masami Hiramatsu (Google) Committed by Steven Rostedt (Google)
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function_graph: Handle tail calls for stack unwinding 

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
Link: https://lore.kernel.org/linux-trace-kernel/20240603190821.717065217@goodmis.org



Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Florent Revest <revest@chromium.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: bpf <bpf@vger.kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Guo Ren <guoren@kernel.org>
Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 7aa1eaef

kernel/trace/fgraph.c

+16 −3
Original line number Diff line number Diff line
@@ -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);