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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2019-11-14 14:39:35 -0500
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2019-11-14 22:45:47 -0500
commit0567d6809182df53da03636fad36c507c5cf07a5 (patch)
treefc9c3c407546b885a43fc68180e0851b219d3b3f /kernel/trace
parent36b3615dc3b625c8b587f34e413a600f7ac16403 (diff)
ftrace: Add modify_ftrace_direct()
Add a new function modify_ftrace_direct() that will allow a user to update an existing direct caller to a new trampoline, without missing hits due to unregistering one and then adding another. Link: https://lore.kernel.org/r/20191109022907.6zzo6orhxpt5n2sv@ast-mbp.dhcp.thefacebook.com Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/ftrace.c78
1 files changed, 78 insertions, 0 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 82ef8d60a42b..834f3556ea1e 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5160,6 +5160,84 @@ 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,
+};
+
+/**
+ * modify_ftrace_direct - Modify an existing direct call to call something else
+ * @ip: The instruction pointer to modify
+ * @old_addr: The address that the current @ip calls directly
+ * @new_addr: The address that the @ip should call
+ *
+ * This modifies a ftrace direct caller at an instruction pointer without
+ * having to disable it first. The direct call will switch over to the
+ * @new_addr without missing anything.
+ *
+ * Returns: zero on success. Non zero on error, which includes:
+ * -ENODEV : the @ip given has no direct caller attached
+ * -EINVAL : the @old_addr does not match the current direct caller
+ */
+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;
+
+ ip = rec->ip;
+ WARN_ON(!(rec->flags & FTRACE_FL_DIRECT));
+ }
+
+ ret = -EINVAL;
+ if (entry->direct != old_addr)
+ goto out_unlock;
+
+ /*
+ * By setting a stub function at the same address, we force
+ * the code to call the iterator and the direct_ops helper.
+ * This means that @ip does not call the direct call, and
+ * we can simply modify it.
+ */
+ 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;
+
+ /*
+ * By removing the stub, we put back the direct call, calling
+ * the @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 */
/**