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

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Message-ID: <20180105120131.GA417@jagdpanzerIV>
Date:   Fri, 5 Jan 2018 21:01:31 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        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 (01/05/18 19:21), Sergey Senozhatsky wrote:
> >     print_symbol() is an old weird API. It has been
> >     obsoleted by printk() and %pS format specifier.
> 
> I wouldn't. let's drop the "weird" part.

hm...

you are right, it is weird. and the weird part here is that
print_symbol() is used for things like __show_regs()

       print_symbol("PC is at %s\n", instruction_pointer(regs));
       print_symbol("LR is at %s\n", regs->ARM_lr);
       printk("pc : [<%08lx>]    lr : [<%08lx>]    psr: %08lx\n",
              regs->ARM_pc, regs->ARM_lr, regs->ARM_cpsr);

or for EMERG error reporting

        pr_emerg("unexpected fault for address: 0x%08lx, last fault for address: 0x%08lx\n",
                 addr, my_reason->addr);
        print_pte(addr);
       print_symbol(KERN_EMERG "faulting IP is at %s\n", regs->ip);
       print_symbol(KERN_EMERG "last faulting IP was at %s\n", my_reason->ip);
 #ifdef __i386__
        pr_emerg("eax: %08lx   ebx: %08lx   ecx: %08lx   edx: %08lx\n",
                 regs->ax, regs->bx, regs->cx, regs->dx);

or for error reporting in sysfs

               print_symbol("fill_read_buffer: %s returned bad count\n",
                       (unsigned long)ops->show);

and so on.

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).

	-ss