linux-kernel - Re: [PATCH 03/10] ftrace: Add register_ftrace

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Message-ID: <20191114140559.5dd40402@gandalf.local.home>
Date:   Thu, 14 Nov 2019 14:05:59 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        X86 ML <x86@...nel.org>, Nadav Amit <nadav.amit@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Song Liu <songliubraving@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 03/10] ftrace: Add register_ftrace_direct()

On Thu, 14 Nov 2019 13:48:27 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> The main reason, is that then we need to add another arch specific
> change, where as, the solution I suggested doesn't need anything new.
> The less arch specific code we need the better.

Here's the change, to see how easy it is (compiled tested only):

/* still needs comments */

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 82ef8d60a42b..4231571db30f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5160,6 +5160,59 @@ int unregister_ftrace_direct(unsigned long ip, unsigned long addr)
 	return ret;
 }
 EXPORT_SYMBOL_GPL(unregister_ftrace_direct);
+
+static struct ftrace_ops stub_ops = {
+	.func		= ftrace_stub,
+};
+
+int modify_ftrace_direct(unsigned long ip,
+			 unsigned long old_addr, unsigned long new_addr)
+{
+	struct ftrace_func_entry *entry;
+	struct dyn_ftrace *rec;
+	int ret = -ENODEV;
+
+	mutex_lock(&direct_mutex);
+	entry = __ftrace_lookup_ip(direct_functions, ip);
+	if (!entry) {
+		/* OK if it is off by a little */
+		rec = lookup_rec(ip, ip);
+		if (!rec || rec->ip == ip)
+			goto out_unlock;
+
+		entry = __ftrace_lookup_ip(direct_functions, rec->ip);
+		if (!entry)
+			goto out_unlock;
+
+		WARN_ON(!(rec->flags & FTRACE_FL_DIRECT));
+	}
+
+	ret = -EINVAL;
+	if (entry->direct != old_addr)
+		goto out_unlock;
+
+	ret = ftrace_set_filter_ip(&stub_ops, ip, 0, 0);
+	if (ret)
+		goto out_unlock;
+
+	ret = register_ftrace_function(&stub_ops);
+	if (ret) {
+		ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
+		goto out_unlock;
+	}
+
+	entry->direct = new_addr;
+
+	unregister_ftrace_function(&stub_ops);
+	ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
+
+	ret = 0;
+
+ out_unlock:
+	mutex_unlock(&direct_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(modify_ftrace_direct);
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 /**


-- Steve