Re: [PATCH] kernel/trace: Add TRACING_ALLOW_PRINTK config option

[Nicolas Boichat]

On Thu, Jun 25, 2020 at 12:04 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Wed, 24 Jun 2020 16:45:24 +0800
> Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote:
>
> > trace_printk is only meant as a debugging tool, and should never be
> > compiled into production code without source code changes, as
> > indicated by the warning that shows up on boot if any trace_printk
> > is called:
> >  **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
> >  **                                                      **
> >  ** trace_printk() being used. Allocating extra memory.  **
> >  **                                                      **
> >  ** This means that this is a DEBUG kernel and it is     **
> >  ** unsafe for production use.                           **
> >
> > If this option is set to n, the kernel will generate a build-time
> > error if trace_printk is used.
> >
> > Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
>
> Interesting. Note, this will prevent modules with trace_printk from
> being loaded as well.

Err, all of these changes are in macros (nothing gets built in the
kernel), so this will prevent modules with trace_printk from being
_built_.

Now, if you set the option to =y when building the module (separately,
even though the rest of the kernel has =n) then I don't see why the
module could not be loaded.

>
> -- Steve