linux-kernel - Re: [RFC PATCH 1/1] tracepoints: tree-wide: Replace %p with %px

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Date:   Wed, 14 Oct 2020 11:35:17 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH 1/1] tracepoints: tree-wide: Replace %p with %px

On Thu, 15 Oct 2020 00:11:04 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Wed, 14 Oct 2020 09:38:13 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> 
> Hmm, would you mean we always run such conversion on printing the trace
> buffer for each entry? It could be much overhead because we need allocate
> memory (%p->%px increase 1 byte) and format conversion (with copying it).

I was thinking of having a single buffer allocated to the iterator (could
increase in size when needed). Really, the output isn't that time critical,
and running a conversion on all events each time shouldn't be that bad. And
if it is, we could have a cache in the iter for a set of events to handle.
Note, the conversion only needs to happen for events that have a %p in the
fmt, and only those need to be cached.

Then those buffers could be freed when the iter is freed.

> Maybe we can avoid repeating it using a kind of cache, but it also consumes
> memory. And as I pointed, the security reason is meaningless because there
> are raw addresses in raw data which user can read...
> Could you tell me what is your point? Making the code change as small as
> possible?
> 

It's about not having to worry about this in the future. Otherwise, we'll
be playing whack-a-mole on making all %px in new trace events.

-- Steve