linux-kernel - [PATCH] ftrace: warn on failure to disable mcount callers

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Message-ID: <alpine.DEB.1.10.0808201237210.27481@gandalf.stny.rr.com>
Date:	Wed, 20 Aug 2008 12:38:27 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] ftrace: warn on failure to disable mcount callers


With the recent updates to ftrace, there should not be any failures when
modifying the code. If there is, then we need to warn about it.

This patch has a cleaned up version of the code that I used to discover
that the weak symbols were causing failures. 

Signed-off-by: Steven Rostedt <srostedt@...hat.com>
---
 kernel/trace/ftrace.c |   25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

Index: linux-tip.git/kernel/trace/ftrace.c
===================================================================
--- linux-tip.git.orig/kernel/trace/ftrace.c	2008-08-20 11:56:12.000000000 -0400
+++ linux-tip.git/kernel/trace/ftrace.c	2008-08-20 12:20:45.000000000 -0400
@@ -574,6 +574,16 @@ static void ftrace_shutdown_replenish(vo
 	ftrace_pages->next = (void *)get_zeroed_page(GFP_KERNEL);
 }
 
+static void print_ip_ins(const char *fmt, unsigned char *p)
+{
+	int i;
+
+	printk(KERN_CONT "%s", fmt);
+
+	for (i = 0; i < MCOUNT_INSN_SIZE; i++)
+		printk(KERN_CONT "%s%02x", i ? ":" : "", p[i]);
+}
+
 static int
 ftrace_code_disable(struct dyn_ftrace *rec)
 {
@@ -588,6 +598,21 @@ ftrace_code_disable(struct dyn_ftrace *r
 
 	failed = ftrace_modify_code(ip, call, nop);
 	if (failed) {
+		switch (failed) {
+		case 1:
+			pr_info("WARNING: ftrace faulted on modifying ");
+			print_ip_sym(ip);
+			break;
+		case 2:
+			pr_info("WARNING: ftrace failed to modify ");
+			print_ip_sym(ip);
+			print_ip_ins(" expected: ", call);
+			print_ip_ins(" actual: ", (unsigned char *)ip);
+			print_ip_ins(" replace: ", nop);
+			printk(KERN_CONT "\n");
+			break;
+		}
+
 		rec->flags |= FTRACE_FL_FAILED;
 		return 0;
 	}

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