On Mon, 12 Jun 2023 22:04:28 -0700
Yonghong Song <yhs@xxxxxxxx> wrote:
> Thanks for explanation! It would be great if we can put more details in
> this email into the commit message!
I agree.
This is the patch I just pulled into my queue:
From: Jiri Olsa <jolsa@xxxxxxxxxx>
Date: Sun, 11 Jun 2023 15:00:29 +0200
Subject: [PATCH] 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@xxxxxxxxxx
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Cc: Jackie Liu <liu.yun@xxxxxxxxx>
Suggested-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
Documentation/trace/ftrace.rst | 6 ++++++
include/linux/ftrace.h | 1 +
kernel/trace/ftrace.c | 37 ++++++++++++++++++++++++++++++++++
3 files changed, 44 insertions(+)
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index df2d3e57a83f..b7308ab10c0e 100644
--- 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 49f279f4c3a1..8e59bd954153 100644
--- 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 764668467155..b24c573934af 100644
--- 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);
--
2.39.2
