ftrace: Show all functions with addresses in available_filter_functions_addrs

Adding new available_filter_functions_addrs file that shows all available
functions (same as available_filter_functions) together with addresses,
like:

  # cat available_filter_functions_addrs | head
  ffffffff81000770 __traceiter_initcall_level
  ffffffff810007c0 __traceiter_initcall_start
  ffffffff81000810 __traceiter_initcall_finish
  ffffffff81000860 trace_initcall_finish_cb
  ...

Note displayed address is the patch-site address and can differ from
/proc/kallsyms address.

It's useful to have address avilable for traceable symbols, so we don't
need to allways cross check kallsyms with available_filter_functions
(or the other way around) and have all the data in single file.

For backwards compatibility reasons we can't change the existing
available_filter_functions file output, but we need to add new file.

The problem is that we need to do 2 passes:

 - through available_filter_functions and find out if the function is traceable
 - through /proc/kallsyms to get the address for traceable function

Having available_filter_functions symbols together with addresses allow
us to skip the kallsyms step and we are ok with the address in
available_filter_functions_addr not being the function entry, because
kprobe_multi uses fprobe and that handles both entry and patch-site
address properly.

We have 2 interfaces how to create kprobe_multi link:

  a) passing symbols to kernel

     1) user gathers symbols and need to ensure that they are
        trace-able -> pass through available_filter_functions file

     2) kernel takes those symbols and translates them to addresses
        through kallsyms api

     3) addresses are passed to fprobe/ftrace through:

         register_fprobe_ips
         -> ftrace_set_filter_ips

  b) passing addresses to kernel

     1) user gathers symbols and needs to ensure that they are
        trace-able -> pass through available_filter_functions file

     2) user takes those symbols and translates them to addresses
       through /proc/kallsyms

     3) addresses are passed to the kernel and kernel calls:

         register_fprobe_ips
         -> ftrace_set_filter_ips

The new available_filter_functions_addrs file helps us with option b),
because we can make 'b 1' and 'b 2' in one step - while filtering traceable
functions, we get the address directly.

Link: https://lore.kernel.org/linux-trace-kernel/20230611130029.1202298-1-jolsa@kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Tested-by: Jackie Liu <liuyun01@kylinos.cn> # x86
Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index df2d3e5..b7308ab 100644 (file)
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -324,6 +324,12 @@ of ftrace. Here is a list of some of the key files:
        "set_graph_function", or "set_graph_notrace".
        (See the section "dynamic ftrace" below for more details.)
 
+  available_filter_functions_addrs:
+
+       Similar to available_filter_functions, but with address displayed
+       for each function. The displayed address is the patch-site address
+       and can differ from /proc/kallsyms address.
+
   dyn_ftrace_total_info:
 
        This file is for debugging purposes. The number of functions that

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 49f279f..8e59bd9 100644 (file)
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -633,6 +633,7 @@ enum {
        FTRACE_ITER_MOD         = (1 << 5),
        FTRACE_ITER_ENABLED     = (1 << 6),
        FTRACE_ITER_TOUCHED     = (1 << 7),
+       FTRACE_ITER_ADDRS       = (1 << 8),
 };
 
 void arch_ftrace_update_code(int command);

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7646684..b24c573 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3861,6 +3861,9 @@ static int t_show(struct seq_file *m, void *v)
        if (!rec)
                return 0;
 
+       if (iter->flags & FTRACE_ITER_ADDRS)
+               seq_printf(m, "%lx ", rec->ip);
+
        if (print_rec(m, rec->ip)) {
                /* This should only happen when a rec is disabled */
                WARN_ON_ONCE(!(rec->flags & FTRACE_FL_DISABLED));
@@ -3996,6 +3999,30 @@ ftrace_touched_open(struct inode *inode, struct file *file)
        return 0;
 }
 
+static int
+ftrace_avail_addrs_open(struct inode *inode, struct file *file)
+{
+       struct ftrace_iterator *iter;
+       int ret;
+
+       ret = security_locked_down(LOCKDOWN_TRACEFS);
+       if (ret)
+               return ret;
+
+       if (unlikely(ftrace_disabled))
+               return -ENODEV;
+
+       iter = __seq_open_private(file, &show_ftrace_seq_ops, sizeof(*iter));
+       if (!iter)
+               return -ENOMEM;
+
+       iter->pg = ftrace_pages_start;
+       iter->flags = FTRACE_ITER_ADDRS;
+       iter->ops = &global_ops;
+
+       return 0;
+}
+
 /**
  * ftrace_regex_open - initialize function tracer filter files
  * @ops: The ftrace_ops that hold the hash filters
@@ -5916,6 +5943,13 @@ static const struct file_operations ftrace_touched_fops = {
        .release = seq_release_private,
 };
 
+static const struct file_operations ftrace_avail_addrs_fops = {
+       .open = ftrace_avail_addrs_open,
+       .read = seq_read,
+       .llseek = seq_lseek,
+       .release = seq_release_private,
+};
+
 static const struct file_operations ftrace_filter_fops = {
        .open = ftrace_filter_open,
        .read = seq_read,
@@ -6377,6 +6411,9 @@ static __init int ftrace_init_dyn_tracefs(struct dentry *d_tracer)
        trace_create_file("available_filter_functions", TRACE_MODE_READ,
                        d_tracer, NULL, &ftrace_avail_fops);
 
+       trace_create_file("available_filter_functions_addrs", TRACE_MODE_READ,
+                       d_tracer, NULL, &ftrace_avail_addrs_fops);
+
        trace_create_file("enabled_functions", TRACE_MODE_READ,
                        d_tracer, NULL, &ftrace_enabled_fops);