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

[Ross Zwisler]

On Mon, Dec 19, 2022 at 01:31:07PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
> 
> 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@xxxxxxxxxxx>

Reviewed-by: Ross Zwisler <zwisler@xxxxxxxxxx>