ftrace: distinguish kretprobe'd functions in trace logs (76094a2c) · Commits · 戴 / test

Tracing functions via ftrace which have a kretprobe installed on them, can produce misleading output in their trace logs. E.g, consider the correct trace of the following sequence: do_IRQ() { ~ irq_enter(); ~ } Trace log (sample): <idle>-0 [00] 4154504455.781616: irq_enter <- do_IRQ But if irq_enter() has a kretprobe installed on it, the return value stored on the stack at each invocation is modified to divert the return to a kprobe trampoline function called kretprobe_trampoline(). So with this the trace would (currently) look like: <idle>-0 [00] 4154504455.781616: irq_enter <- kretprobe_trampoline Now this is quite misleading to the end user, as it suggests something that didn't actually happen. So just to avoid such misinterpretations, the inlined patch aims to output such a log as: <idle>-0 [00] 4154504455.781616: irq_enter <- [unknown/kretprobe'd] Signed-off-by:

Abhishek Sagar <sagar.abhishek@gmail.com> Acked-by:

Steven Rostedt <srostedt@redhat.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.c

+24 −3

Original line number	Diff line number	Diff line
		@@ -27,6 +27,7 @@
		#include <linux/poll.h>
		#include <linux/gfp.h>
		#include <linux/fs.h>
		#include <linux/kprobes.h>
		#include <linux/writeback.h>

		#include <linux/stacktrace.h>
		@@ -1199,6 +1200,20 @@ static void s_stop(struct seq_file m, void p)
		mutex_unlock(&trace_types_lock);
		}

		#define KRETPROBE_MSG "[unknown/kretprobe'd]"

		#ifdef CONFIG_KRETPROBES
		static inline int kretprobed(unsigned long addr)
		{
		return addr == (unsigned long)kretprobe_trampoline;
		}
		#else
		static inline int kretprobed(unsigned long addr)
		{
		return 0;
		}
		#endif /* CONFIG_KRETPROBES */

		static int
		seq_print_sym_short(struct trace_seq s, const char fmt, unsigned long address)
		{
		@@ -1434,6 +1449,9 @@ print_lat_fmt(struct trace_iterator *iter, unsigned int trace_idx, int cpu)
		case TRACE_FN:
		seq_print_ip_sym(s, entry->fn.ip, sym_flags);
		trace_seq_puts(s, " (");
		if (kretprobed(entry->fn.parent_ip))
		trace_seq_puts(s, KRETPROBE_MSG);
		else
		seq_print_ip_sym(s, entry->fn.parent_ip, sym_flags);
		trace_seq_puts(s, ")\n");
		break;
		@@ -1514,6 +1532,9 @@ static int print_trace_fmt(struct trace_iterator *iter)
		ret = trace_seq_printf(s, " <-");
		if (!ret)
		return 0;
		if (kretprobed(entry->fn.parent_ip))
		ret = trace_seq_puts(s, KRETPROBE_MSG);
		else
		ret = seq_print_ip_sym(s, entry->fn.parent_ip,
		sym_flags);
		if (!ret)

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