linux-kernel - Re: [PATCH -next] lib/vsprintf: Make function pointer

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Date:   Mon, 29 Apr 2019 16:30:37 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Yue Haibing <yuehaibing@...wei.com>, sergey.senozhatsky@...il.com,
        andriy.shevchenko@...ux.intel.com, geert+renesas@...der.be,
        me@...in.cc, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH -next] lib/vsprintf: Make function pointer_string static

On Mon 2019-04-29 09:13:20, Steven Rostedt wrote:
> On Mon, 29 Apr 2019 13:08:01 +0200
> Petr Mladek <pmladek@...e.com> wrote:
> 
> > > Looks like commit "vsprintf: Do not check address of well-known
> > > strings" removed the: "static noinline_for_stack"
> > > 
> > > Does pointer_string() need that still?  
> > 
> > Heh, it was removed by mistake and well hidden in the diff.
> > 
> > I have pushed Yue's fix into printk.git, branch
> > for-5.2-vsprintf-hardening
> > 
> > Thanks for the patch.
> 
> But doesn't it still need the "noinline_for_stack", that doesn't look
> like it changed.

Good question. I have just double checked it. And pointer_string() with
"noinline_for_stack" does not make any difference in the stack
usage here.

I actually played with this before:

"noinline_for_stack" is a black magic added by
the commit cf3b429b03e827c7180 ("vsprintf.c: use noinline_for_stack").

It is evidently useful in some cases. But I somehow doubt
that it really makes things better when used everywhere.
Therefore I have got a bit relaxed and omitted it in most
newly added functions that did not affect the results.

They are the same before and after the patchset:

pmladek@...hway:/prace/kernel/linux-printk> objdump -d lib/vsprintf.o | perl scripts/checkstack.pl
0x00000e12 symbol_string [vsprintf.o]:                  248
0x00000e6d symbol_string [vsprintf.o]:                  248
0x000012fb ip6_addr_string_sa [vsprintf.o]:             112
0x00001415 ip6_addr_string_sa [vsprintf.o]:             112
0x000028c6 resource_string.isra.9 [vsprintf.o]:         104
0x00002964 resource_string.isra.9 [vsprintf.o]:         104

Would you like to fix this clearly, for example, rebase and
put both "static noinline_for_stack" back or add yet
another commit or?

IMHO, it is not too important. Anyway, I am open for any
advice. I do not want to create more mess.

Best Regards,
Petr