linux-kernel - Re: [PATCH 00/13] replace print

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Message-ID: <20180105130907.iaketkpmqbhtzpfx@pathway.suse.cz>
Date:   Fri, 5 Jan 2018 14:09:07 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Salter <msalter@...hat.com>,
        Tony Luck <tony.luck@...el.com>,
        David Howells <dhowells@...hat.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        Borislav Petkov <bp@...en8.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Vineet Gupta <vgupta@...opsys.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-c6x-dev@...ux-c6x.org,
        linux-ia64@...r.kernel.org, linux-am33-list@...hat.com,
        linux-sh@...r.kernel.org, linux-edac@...r.kernel.org,
        x86@...nel.org, linux-snps-arc@...ts.infradead.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 00/13] replace print_symbol() with printk()-s

On Fri 2018-01-05 21:23:34, Sergey Senozhatsky wrote:
> On (01/05/18 21:01), Sergey Senozhatsky wrote:
> [..]
> > but, print_symbol() is compiled out on !CONFIG_KALLSYMS systems. so,
> > basically, we compile out some of errors print outs; even more, on ia64
> > ia64_do_show_stack() does nothing when there is no CONFIG_KALLSYMS [all
> > ia64 defconfigs have KALLSYMS_ALL enabled]. printk(%pS), unlike
> > print_symbol(), is not compiled out and prints the function address
> > when symbolic name is not available. but, at a glance, print_symbol()
> > in most of the cases has printk(registers) next to it or before it, so
> > it doesn't look like we are introducing a regression here by switching
> > to printk(%pS).
> 
> well, if this is a problem, then we can have

I believe that this is not a problem. If it was, we would most likely
need to solve it in the existing printk(%pS) callers.

> but we still have tons printk(%pS) in the kernel and even print_ip_sym()
> (which is not compiled out on !CONFIG_KALLSYMS). so it seems to me that
> we can drop print_symbol()/__print_symbol() and switch to printk(%pS)
> after all.

Exactly.

BTW: print_symbol() looks weird to me because:

   + looks like a normal printk() but
   + only one format specifier (%s) is replaced
   + %s is used to print an address/pointer

IMHO, this is counter-intuitive and even error prone.
Also it makes people using crazy hacks like the one fixed
in 4th patch, see
https://lkml.kernel.org/r/20171211125025.2270-5-sergey.senozhatsky@gmail.com

Best Regards,
Petr