On Tue 2021-03-02 14:49:42, Geert Uytterhoeven wrote:
> Hi Vlastimil, Petr,
>
> On Tue, Mar 2, 2021 at 2:37 PM Vlastimil Babka <vba...@suse.cz> wrote:
> > On 3/2/21 2:29 PM, Petr Mladek wrote:
> > > On Tue 2021-03-02 13:51:35, Geert Uytterhoeven wrote:
> > >> > > > +
> > >> > > > +
> > >> > > > pr_warn("**********************************************************\n");
> > >> > > > + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE
> > >> > > > NOTICE **\n");
> > >> > > > + pr_warn("**
> > >> > > > **\n");
> > >> > > > + pr_warn("** This system shows unhashed kernel memory
> > >> > > > addresses **\n");
> > >> > > > + pr_warn("** via the console, logs, and other interfaces.
> > >> > > > This **\n");
> > >> > > > + pr_warn("** might reduce the security of your system.
> > >> > > > **\n");
> > >> > > > + pr_warn("**
> > >> > > > **\n");
> > >> > > > + pr_warn("** If you see this message and you are not
> > >> > > > debugging **\n");
> > >> > > > + pr_warn("** the kernel, report this immediately to your
> > >> > > > system **\n");
> > >> > > > + pr_warn("** administrator!
> > >> > > > **\n");
> > >> > > > + pr_warn("**
> > >> > > > **\n");
> > >> > > > + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE
> > >> > > > NOTICE **\n");
> > >> > > > +
> > >> > > > pr_warn("**********************************************************\n");
> > >> > > > +
> > >> > > > + return 0;
> > >> > > > +}
> > >> > > > +early_param("no_hash_pointers", no_hash_pointers_enable);
> > >> > >
> > >> > > While bloat-o-meter is not smart enough to notice the real size
> > >> > > impact,
> > >> > > this does add more than 500 bytes of string data to the kernel.
> > >> > > Do we really need such a large message?
> > >> > > Perhaps the whole no_hash_pointers machinery should be protected by
> > >> > > "#ifdef CONFIG_DEBUG_KERNEL"?
> >
> > I think it's a no-go only when enabling such option equals to
> > "no_hash_pointers"
> > being always passed. What Geert suggests is that you need both
> > CONFIG_DEBUG_KERNEL *and* no_hash_pointers and that's different.
>
> Exactly.
>
> > So this is basically a kernel tinyfication issue, right? Is that still
> > pursued
> > today? Are there better config options suitable for this than
> > CONFIG_DEBUG_KERNEL?
>
> As long as I hear about products running Linux on SoCs with 10 MiB of
> SRAM, I think the answer is yes.
> I'm not immediately aware of a better config option. There are no more
> TINY options left, and EXPERT selects DEBUG_KERNEL.
DEBUG_KERNEL might actually makes sense. A possibility to see real
pointers might be pretty useful for the other debugging code.
It is a common thing.
DEBUG_KERNEL is even needed for many basics debugging helpers,
for example, for FRAME_POINTERS.
So, if it would be good for SoCs...
> > >> > Would placing the strings into an __initconst array help?
> > >>
> > >> That would indeed help to reduce run-time memory consumption.
> > >
> > > Sure. We could do this. Do you want to send a patch, please?
>
> Added to my list.
>
> > >> It would not solve the raw kernel size increase.
> > >
> > > I see. Well, the compression should be pretty efficient
> > > for a text (with many spaces).
>
> My worry is not about the medium for storing the kernel image, but the
> RAM where the kernel image is loaded. The former is usually less
> restricted in size, and easier to expand, than the latter,
Well, the __initconst might be enough then.
I personally do not have any preference whether to do __initconst
or DEBUG_KERNEL or both. We should just keep it simple and
do not over engineer it.
Best Regards,
Petr
