linux-kernel - Re: [PATCH 4/5 v2] x86 boot: show pfn addresses in hex not decimal in some kernel info printks

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Date:	Mon, 30 Jun 2008 09:58:28 +0200
From:	"Alexander van Heukelum" <heukelum@...tmail.fm>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Johannes Berg" <johannes@...solutions.net>
Cc:	"Paul Jackson" <pj@....com>, "H. Peter Anvin" <hpa@...or.com>,
	yhlu.kernel@...il.com, "Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>, steiner@....com,
	travis@....com, linux-kernel@...r.kernel.org, ying.huang@...el.com,
	"Andi Kleen" <andi@...stfloor.org>
Subject: Re: [PATCH 4/5 v2] x86 boot: show pfn addresses in hex not decimal in
 some kernel info printks

On Wed, 25 Jun 2008 08:19:13 -0700 (PDT), "Linus Torvalds"
<torvalds@...ux-foundation.org> said:
> On Wed, 25 Jun 2008, Johannes Berg wrote:
> > 
> > In networking, we've gone through various incarnations of print_mac()
> > which is similar to the sym() macro Paul proposed, and it turned out to
> > be undesirable because of the way it interacts with static inlines that
> > only optionally contain code at all, the print_mac() function call is
> > still emitted by the compiler. People experimented with marking it
> > __pure but that had other problems.
> 
> You don't even have to go that esoteric.
> 
> Just printing things like "sector_t" or "u64" is painful, because the 
> exact type depends on config options and/or architecture.
> 
> > It would be nice to be able to say
> > 
> > u8 *eaddr;
> > 
> > printk(... %M ..., eaddr);
> 
> For special things, I do think we should extend the format more, and 
> forget about single-character names. It would be lovely to do them as
> %[mac], %[u64], %[symbol] or similar. Because once you don't rely on gcc 
> checking the string, you can do it.

That would confuse the gcc format string checking... A solution that
just crossed my mind is leaving the format string as is (i.e., "%p"),
but prepending it with a special linux-specific string which does not
confuse gcc. Like: "&mac%p"... for simplicity & can be considered always
special in printk, and && can stand for a literal &. (or pick any
other character that is not used frequently in format strings and is
not %, of course.)

> The problem is that right now we absolutely _do_ rely on gcc checking the 
> string, and as such we're forced to use standard patterns, and standard 
> patterns _only_. And that means that %M isn't an option, but also that if 
> we want symbolic names we'd have to use %p, and not some extension.

"&%p" could then be used for a symbol-lookup.

It doesn't help u64, though, but isn't it about time to unify u64 to
"unsigned long long" everywhere, anyhow? Is there any argument against
that except that a big sweep is necessary to clean up new warnings due
to printk format strings?

Greetings,
    Alexander

> But once you drop the 'standard patterns' requirement, I do think you 
> should drop it _entirely_, and not just extend it with some pissant 
> single-character unreadable mess.
> 
> 				Linus
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> 
-- 
  Alexander van Heukelum
  heukelum@...tmail.fm

-- 
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