linux-kernel - Re: [PATCH 1/2] tracing: Add a way to filter function addresses to function names

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Date:   Mon, 19 Dec 2022 13:57:18 -0700
From:   Ross Zwisler <zwisler@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Zheng Yejian <zhengyejian1@...wei.com>
Subject: Re: [PATCH 1/2] tracing: Add a way to filter function addresses to
 function names

On Mon, Dec 19, 2022 at 01:31:07PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> 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 "!=".
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>

Reviewed-by: Ross Zwisler <zwisler@...gle.com>