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Subject[PATCH v2] ftrace: warn on failure to disable mcount callers

On Thu, 21 Aug 2008, Ingo Molnar wrote:

>
> * Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > + pr_info("WARNING: ftrace faulted on modifying ");
> > + print_ip_sym(ip);
>
> please use the WARN() API, so that it gets picked up by automation.
>
> Ingo
>

[
Added WARN_ON as requested above.
]


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@redhat.com>
---
kernel/trace/ftrace.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

Index: linux-tip.git/kernel/trace/ftrace.c
===================================================================
--- linux-tip.git.orig/kernel/trace/ftrace.c 2008-08-20 21:58:19.000000000 -0400
+++ linux-tip.git/kernel/trace/ftrace.c 2008-08-21 10:19:09.000000000 -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 +598,23 @@ ftrace_code_disable(struct dyn_ftrace *r

failed = ftrace_modify_code(ip, call, nop);
if (failed) {
+ switch (failed) {
+ case 1:
+ WARN_ON_ONCE(1);
+ pr_info("ftrace faulted on modifying ");
+ print_ip_sym(ip);
+ break;
+ case 2:
+ WARN_ON_ONCE(1);
+ pr_info("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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