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

[Steven Rostedt]

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@xxxxxxxxxx>
---
 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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