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83f74441bc
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>
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