Commit 223918e3 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

ftrace: Add ftrace_graph_ret_addr() stack unwinding helpers 



When function graph tracing is enabled for a function, ftrace modifies
the stack by replacing the original return address with the address of a
hook function (return_to_handler).

Stack unwinders need a way to get the original return address.  Add an
arch-independent helper function for that named ftrace_graph_ret_addr().

This adds two variations of the function: one depends on
HAVE_FUNCTION_GRAPH_RET_ADDR_PTR, and the other relies on an index state
variable.

The former is recommended because, in some cases, the latter can cause
problems when the unwinder skips stack frames.  It can get out of sync
with the ret_stack index and wrong addresses can be reported for the
stack trace.

Once all arches have been ported to use
HAVE_FUNCTION_GRAPH_RET_ADDR_PTR, we can get rid of the distinction.

Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/36bd90f762fc5e5af3929e3797a68a64906421cf.1471607358.git.jpoimboe@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 9a7c348b

include/linux/ftrace.h

+10 −0
Original line number Diff line number Diff line
@@ -814,6 +814,9 @@ extern int 
ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,

			 unsigned long frame_pointer, unsigned long *retp);



unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,

				    unsigned long ret, unsigned long *retp);



/*

 * Sometimes we don't want to trace a function with the function

 * graph tracer but we want them to keep traced by the usual function
@@ -875,6 +878,13 @@ static inline int task_curr_ret_stack(struct task_struct *tsk) 
	return -1;

}



static inline unsigned long

ftrace_graph_ret_addr(struct task_struct *task, int *idx, unsigned long ret,

		      unsigned long *retp)

{

	return ret;

}



static inline void pause_graph_tracing(void) { }

static inline void unpause_graph_tracing(void) { }

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

kernel/trace/trace_functions_graph.c

+58 −0
Original line number Diff line number Diff line
@@ -284,6 +284,64 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer) 
	return ret;

}



/**

 * ftrace_graph_ret_addr - convert a potentially modified stack return address

 *			   to its original value

 *

 * This function can be called by stack unwinding code to convert a found stack

 * return address ('ret') to its original value, in case the function graph

 * tracer has modified it to be 'return_to_handler'.  If the address hasn't

 * been modified, the unchanged value of 'ret' is returned.

 *

 * 'idx' is a state variable which should be initialized by the caller to zero

 * before the first call.

 *

 * 'retp' is a pointer to the return address on the stack.  It's ignored if

 * the arch doesn't have HAVE_FUNCTION_GRAPH_RET_ADDR_PTR defined.

 */

#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR

unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,

				    unsigned long ret, unsigned long *retp)

{

	int index = task->curr_ret_stack;

	int i;



	if (ret != (unsigned long)return_to_handler)

		return ret;



	if (index < -1)

		index += FTRACE_NOTRACE_DEPTH;



	if (index < 0)

		return ret;



	for (i = 0; i <= index; i++)

		if (task->ret_stack[i].retp == retp)

			return task->ret_stack[i].ret;



	return ret;

}

#else /* !HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */

unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,

				    unsigned long ret, unsigned long *retp)

{

	int task_idx;



	if (ret != (unsigned long)return_to_handler)

		return ret;



	task_idx = task->curr_ret_stack;



	if (!task->ret_stack || task_idx < *idx)

		return ret;



	task_idx -= *idx;

	(*idx)++;



	return task->ret_stack[task_idx].ret;

}

#endif /* HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */



int __trace_graph_entry(struct trace_array *tr,

				struct ftrace_graph_ent *trace,

				unsigned long flags,

CRA Git | Maintained and supported by SUSTech CRA and CCSE