linux-kernel - Re: [PATCHv4 5/6] symbol lookup: introduce dereference_symbol

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Date:   Wed, 6 Dec 2017 19:46:56 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        James Bottomley <jejb@...isc-linux.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 5/6] symbol lookup: introduce
 dereference_symbol_descriptor()

On (12/06/17 11:32), Petr Mladek wrote:
[..]
> > diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
> > index aa0a776c817a..02745028e909 100644
> > --- a/Documentation/printk-formats.txt
> > +++ b/Documentation/printk-formats.txt
> > @@ -61,41 +61,31 @@ Symbols/Function Pointers
> >  
> >  ::
> >  
> > -	%pF	versatile_init+0x0/0x110
> > -	%pf	versatile_init
> > -	%pS	versatile_init+0x0/0x110
> > -	%pSR	versatile_init+0x9/0x110
> > +	%pS     versatile_init+0x0/0x110
> > +	%ps     versatile_init
> > +	%pF     versatile_init+0x0/0x110
> > +	%pf     versatile_init
> > +	%pSR    versatile_init+0x9/0x110
> >  		(with __builtin_extract_return_addr() translation)
> > -	%ps	versatile_init
> > -	%pB	prev_fn_of_versatile_init+0x88/0x88
> > +	%pB     prev_fn_of_versatile_init+0x88/0x88
> 
> I was curious why so many lines were changed here. You converted
> the 2nd tab to spaces. I put back the tab. The result is:

ew... how did that happen. thanks for fixing up.

> > +static inline void *dereference_symbol_descriptor(void *ptr)
> > +{
> > +#ifdef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
> > +	struct module *mod;
> > +
> > +	ptr = dereference_kernel_function_descriptor(ptr);
> > +	if (is_ksym_addr((unsigned long)ptr))
> > +		return ptr;
> > +
> > +	preempt_disable();
> > +	mod = __module_address((unsigned long)ptr);
> > +	preempt_enable();
> > +
> > +	if (mod)
> > +		ptr = dereference_module_function_descriptor(mod, ptr);
> > +#endif
> > +	return ptr;
> > +}
> 
> It is a bit too long for an inline function but I did not find a
> better solution. It should always be defined and all suitable
> .c files are compiled only under certain configuration. Well,
> it is a nop on most architectures.

or we can move dereference_symbol_descriptor() to vsprintf.c,
since all the functions it depends on are now available either
as exported symbols or via kallsyms header file. not that it
annoys me, so we can keep it as it is.

	-ss