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ftrace: Add modify_ftrace_direct()

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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>
This commit is contained in:
Steven Rostedt (VMware) 2019-11-14 14:39:35 -05:00
parent 36b3615dc3
commit 0567d68091
2 changed files with 84 additions and 0 deletions
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6
include/linux/ftrace.h
View File

@ -250,6 +250,7 @@ static inline void ftrace_free_mem(struct module *mod, void *start, void *end) {
extern int ftrace_direct_func_count;
int register_ftrace_direct(unsigned long ip, unsigned long addr);
int unregister_ftrace_direct(unsigned long ip, unsigned long addr);
int modify_ftrace_direct(unsigned long ip, unsigned long old_addr, unsigned long new_addr);
struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr);
#else
# define ftrace_direct_func_count 0
@ -261,6 +262,11 @@ static inline int unregister_ftrace_direct(unsigned long ip, unsigned long addr)
{
return -ENODEV;
}
static inline int modify_ftrace_direct(unsigned long ip,
unsigned long old_addr, unsigned long new_addr)
{
return -ENODEV;
}
static inline struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr)
{
return NULL;

78
kernel/trace/ftrace.c
View File

@ -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 */
/**