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

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Date:   Mon, 29 Apr 2019 09:42:30 -0700
From:   Joe Perches <joe@...ches.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>
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 at 10:39 -0400, Steven Rostedt wrote:
> [ added Joe ]
> > 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").
> 
> From what I understand, "noinline_for_stack" is just noinline and the
> "for_stack" part is just to document that the noinline is used for
> stack purposes. If the compiler doesn't inline the function without the
> noinline, then it wont make any difference.
> 
> The point was to not inline the function because it can be used in
> stack critical areas, and that it's better to do the call than to
> increase the stack.

It was added because of %pV is recursive and recursive
functions can eat
a lot of stack.

Using noinline_for_stack was just a bit more self-documenting.

I do still think it's a useful notation.