tracing: Add a way to filter function addresses to function names

There's been several times where an event records a function address in
its field and I needed to filter on that address for a specific function
name. It required looking up the function in kallsyms, finding its size,
and doing a compare of "field >= function_start && field < function_end".

But this would change from boot to boot and is unreliable in scripts.
Also, it is useful to have this at boot up, where the addresses will not
be known. For example, on the boot command line:

  trace_trigger="initcall_finish.traceoff if func.function == acpi_init"

To implement this, add a ".function" prefix, that will check that the
field is of size long, and the only operations allowed (so far) are "=="
and "!=".

Link: https://lkml.kernel.org/r/20221219183213.916833763@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Ross Zwisler <zwisler@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 33e0b4f8ebe6..b07931ad97de 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2822,7 +2822,7 @@ static __init int setup_trace_triggers(char *str)
 		if (!trigger)
 			break;
 		bootup_triggers[i].event = strsep(&trigger, ".");
-		bootup_triggers[i].trigger = strsep(&trigger, ".");
+		bootup_triggers[i].trigger = trigger;
 		if (!bootup_triggers[i].trigger)
 			break;
 	}