Reason for unused flags argument in trace_raw_output_* function?

Reason for unused flags argument in trace_raw_output_* function?

[William Cohen]

Hi,

I have some code that analyzes x86_64 binaries (https://developers.redhat.com/articles/2021/08/09/debugging-function-parameters-
dyninst#liveness_analysis) and list which function parameters are unused.  I noticed that trace_raw_output_* functions have an unused flags argument.  I assume this is is to make the argument list match up with some other function, but I couldn't see which function(s) the trace_raw_output_* functions are trying to match up with.  Which functions are the trace_raw_output_* function's arguments trying to match?


-Will Cohen

Re: Reason for unused flags argument in trace_raw_output_* function?

[Steven Rostedt]

On Wed, 6 Oct 2021 23:49:22 -0400
William Cohen <wcohen@redhat.com> wrote:

> Hi,
> 
> I have some code that analyzes x86_64 binaries
> (https://developers.redhat.com/articles/2021/08/09/debugging-function-parameters-
> dyninst#liveness_analysis) and list which function parameters are unused.
>  I noticed that trace_raw_output_* functions have an unused flags
> argument.  I assume this is is to make the argument list match up with
> some other function, but I couldn't see which function(s) the
> trace_raw_output_* functions are trying to match up with.  Which
> functions are the trace_raw_output_* function's arguments trying to match?
> 

The match of other printing functions is in kernel/trace/trace_output.c

And is called from kernel/trace/trace.c where one place it does pass in
flags:


static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
{
	[..]
	if (event)
		return event->funcs->trace(iter, sym_flags, event);

Now if they are still used, is something we should investigate.

This code has changed a lot over the years when that "flags" parameter was
introduced. It could now just be a relic from the old implementations.

Thanks for pointing this out. If I get time I'll look deeper into it, but
feel free to look at it yourself.

-- Steve

Re: Reason for unused flags argument in trace_raw_output_* function?

[William Cohen]

On 10/7/21 09:20, Steven Rostedt wrote:
> On Wed, 6 Oct 2021 23:49:22 -0400
> William Cohen <wcohen@redhat.com> wrote:
> 
>> Hi,
>>
>> I have some code that analyzes x86_64 binaries
>> (https://developers.redhat.com/articles/2021/08/09/debugging-function-parameters-
>> dyninst#liveness_analysis) and list which function parameters are unused.
>>  I noticed that trace_raw_output_* functions have an unused flags
>> argument.  I assume this is is to make the argument list match up with
>> some other function, but I couldn't see which function(s) the
>> trace_raw_output_* functions are trying to match up with.  Which
>> functions are the trace_raw_output_* function's arguments trying to match?
>>
> 
> The match of other printing functions is in kernel/trace/trace_output.c
> 
> And is called from kernel/trace/trace.c where one place it does pass in
> flags:
> 
> 
> static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
> {
> 	[..]
> 	if (event)
> 		return event->funcs->trace(iter, sym_flags, event);


Hi Steve,

Thanks for pointing to where the trace_raw_output_* functions are called from.

> 
> Now if they are still used, is something we should investigate.

For the trace_raw_output_* functions the flags arg all seems to be unused.  Are there other trace functions should examining for unused args?  With the extensive macro use I could see where some vestigial unused argument gets left behind.

> 
> This code has changed a lot over the years when that "flags" parameter was
> introduced. It could now just be a relic from the old implementations.
> 
> Thanks for pointing this out. If I get time I'll look deeper into it, but
> feel free to look at it yourself.
> 
> -- Steve
> 

Thanks again,

-Will