fgraph: Create a fgraph.c file to store function graph infrastructure

As the function graph infrastructure can be used by thing other than
tracing, moving the code to its own file out of the trace_functions_graph.c
code makes more sense.

The fgraph.c file will only contain the infrastructure required to hook into
functions and their return code.

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/Makefile

@@ -57,6 +57,7 @@ obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += trace_functions_graph.o
 obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
 obj-$(CONFIG_BLK_DEV_IO_TRACE) += blktrace.o
+obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += fgraph.o
 ifeq ($(CONFIG_BLOCK),y)
 obj-$(CONFIG_EVENT_TRACING) += blktrace.o
 endif

kernel/trace/fgraph.c

@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Infrastructure to took into function calls and returns.
+ * Copyright (c) 2008-2009 Frederic Weisbecker <fweisbec@gmail.com>
+ * Mostly borrowed from function tracer which
+ * is Copyright (c) Steven Rostedt <srostedt@redhat.com>
+ *
+ * Highly modified by Steven Rostedt (VMware).
+ */
+#include <linux/ftrace.h>
+
+#include "trace.h"
+
+static bool kill_ftrace_graph;
+
+/**
+ * ftrace_graph_is_dead - returns true if ftrace_graph_stop() was called
+ *
+ * ftrace_graph_stop() is called when a severe error is detected in
+ * the function graph tracing. This function is called by the critical
+ * paths of function graph to keep those paths from doing any more harm.
+ */
+bool ftrace_graph_is_dead(void)
+{
+	return kill_ftrace_graph;
+}
+
+/**
+ * ftrace_graph_stop - set to permanently disable function graph tracincg
+ *
+ * In case of an error int function graph tracing, this is called
+ * to try to keep function graph tracing from causing any more harm.
+ * Usually this is pretty severe and this is called to try to at least
+ * get a warning out to the user.
+ */
+void ftrace_graph_stop(void)
+{
+	kill_ftrace_graph = true;
+}
+
+/* Add a function return address to the trace stack on thread info.*/
+static int
+ftrace_push_return_trace(unsigned long ret, unsigned long func,
+			 unsigned long frame_pointer, unsigned long *retp)
+{
+	unsigned long long calltime;
+	int index;
+
+	if (unlikely(ftrace_graph_is_dead()))
+		return -EBUSY;
+
+	if (!current->ret_stack)
+		return -EBUSY;
+
+	/*
+	 * We must make sure the ret_stack is tested before we read
+	 * anything else.
+	 */
+	smp_rmb();
+
+	/* The return trace stack is full */
+	if (current->curr_ret_stack == FTRACE_RETFUNC_DEPTH - 1) {
+		atomic_inc(&current->trace_overrun);
+		return -EBUSY;
+	}
+
+	/*
+	 * The curr_ret_stack is an index to ftrace return stack of
+	 * current task.  Its value should be in [0, FTRACE_RETFUNC_
+	 * DEPTH) when the function graph tracer is used.  To support
+	 * filtering out specific functions, it makes the index
+	 * negative by subtracting huge value (FTRACE_NOTRACE_DEPTH)
+	 * so when it sees a negative index the ftrace will ignore
+	 * the record.  And the index gets recovered when returning
+	 * from the filtered function by adding the FTRACE_NOTRACE_
+	 * DEPTH and then it'll continue to record functions normally.
+	 *
+	 * The curr_ret_stack is initialized to -1 and get increased
+	 * in this function.  So it can be less than -1 only if it was
+	 * filtered out via ftrace_graph_notrace_addr() which can be
+	 * set from set_graph_notrace file in tracefs by user.
+	 */
+	if (current->curr_ret_stack < -1)
+		return -EBUSY;
+
+	calltime = trace_clock_local();
+
+	index = ++current->curr_ret_stack;
+	if (ftrace_graph_notrace_addr(func))
+		current->curr_ret_stack -= FTRACE_NOTRACE_DEPTH;
+	barrier();
+	current->ret_stack[index].ret = ret;
+	current->ret_stack[index].func = func;
+	current->ret_stack[index].calltime = calltime;
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+	current->ret_stack[index].fp = frame_pointer;
+#endif
+#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
+	current->ret_stack[index].retp = retp;
+#endif
+	return 0;
+}
+
+int function_graph_enter(unsigned long ret, unsigned long func,
+			 unsigned long frame_pointer, unsigned long *retp)
+{
+	struct ftrace_graph_ent trace;
+
+	trace.func = func;
+	trace.depth = ++current->curr_ret_depth;
+
+	if (ftrace_push_return_trace(ret, func, frame_pointer, retp))
+		goto out;
+
+	/* Only trace if the calling function expects to */
+	if (!ftrace_graph_entry(&trace))
+		goto out_ret;
+
+	return 0;
+ out_ret:
+	current->curr_ret_stack--;
+ out:
+	current->curr_ret_depth--;
+	return -EBUSY;
+}
+
+/* Retrieve a function return address to the trace stack on thread info.*/
+static void
+ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
+			unsigned long frame_pointer)
+{
+	int index;
+
+	index = current->curr_ret_stack;
+
+	/*
+	 * A negative index here means that it's just returned from a
+	 * notrace'd function.  Recover index to get an original
+	 * return address.  See ftrace_push_return_trace().
+	 *
+	 * TODO: Need to check whether the stack gets corrupted.
+	 */
+	if (index < 0)
+		index += FTRACE_NOTRACE_DEPTH;
+
+	if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
+		ftrace_graph_stop();
+		WARN_ON(1);
+		/* Might as well panic, otherwise we have no where to go */
+		*ret = (unsigned long)panic;
+		return;
+	}
+
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+	/*
+	 * The arch may choose to record the frame pointer used
+	 * and check it here to make sure that it is what we expect it
+	 * to be. If gcc does not set the place holder of the return
+	 * address in the frame pointer, and does a copy instead, then
+	 * the function graph trace will fail. This test detects this
+	 * case.
+	 *
+	 * Currently, x86_32 with optimize for size (-Os) makes the latest
+	 * gcc do the above.
+	 *
+	 * Note, -mfentry does not use frame pointers, and this test
+	 *  is not needed if CC_USING_FENTRY is set.
+	 */
+	if (unlikely(current->ret_stack[index].fp != frame_pointer)) {
+		ftrace_graph_stop();
+		WARN(1, "Bad frame pointer: expected %lx, received %lx\n"
+		     "  from func %ps return to %lx\n",
+		     current->ret_stack[index].fp,
+		     frame_pointer,
+		     (void *)current->ret_stack[index].func,
+		     current->ret_stack[index].ret);
+		*ret = (unsigned long)panic;
+		return;
+	}
+#endif
+
+	*ret = current->ret_stack[index].ret;
+	trace->func = current->ret_stack[index].func;
+	trace->calltime = current->ret_stack[index].calltime;
+	trace->overrun = atomic_read(&current->trace_overrun);
+	trace->depth = current->curr_ret_depth--;
+	/*
+	 * We still want to trace interrupts coming in if
+	 * max_depth is set to 1. Make sure the decrement is
+	 * seen before ftrace_graph_return.
+	 */
+	barrier();
+}
+
+/*
+ * Send the trace to the ring-buffer.
+ * @return the original return address.
+ */
+unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
+{
+	struct ftrace_graph_ret trace;
+	unsigned long ret;
+
+	ftrace_pop_return_trace(&trace, &ret, frame_pointer);
+	trace.rettime = trace_clock_local();
+	ftrace_graph_return(&trace);
+	/*
+	 * The ftrace_graph_return() may still access the current
+	 * ret_stack structure, we need to make sure the update of
+	 * curr_ret_stack is after that.
+	 */
+	barrier();
+	current->curr_ret_stack--;
+	/*
+	 * The curr_ret_stack can be less than -1 only if it was
+	 * filtered out and it's about to return from the function.
+	 * Recover the index and continue to trace normal functions.
+	 */
+	if (current->curr_ret_stack < -1) {
+		current->curr_ret_stack += FTRACE_NOTRACE_DEPTH;
+		return ret;
+	}
+
+	if (unlikely(!ret)) {
+		ftrace_graph_stop();
+		WARN_ON(1);
+		/* Might as well panic. What else to do? */
+		ret = (unsigned long)panic;
+	}
+
+	return ret;
+}