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

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Date:   Sat, 11 Nov 2017 13:49:32 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.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>, Petr Mladek <pmladek@...e.com>,
        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,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCHv4 5/6] symbol lookup: introduce
 dereference_symbol_descriptor()

On (11/10/17 10:09), Luck, Tony wrote:
> On Fri, Nov 10, 2017 at 08:48:29AM +0900, Sergey Senozhatsky wrote:
> > -Examples::
> > -
> > -	printk("Going to call: %pF\n", gettimeofday);
> > -	printk("Going to call: %pF\n", p->func);
> > -	printk("%s: called from %pS\n", __func__, (void *)_RET_IP_);
> > -	printk("%s: called from %pS\n", __func__,
> > -				(void *)__builtin_return_address(0));
> > -	printk("Faulted at %pS\n", (void *)regs->ip);
> > -	printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack);
> 
> Did you mean to delete the Examples completely?  Wouldn't it
> be better to just update (s/%pF/%pS/g)?

good question. yes, I think I did it deliberately :) we still
kinda have some sort of "examples", right at the beginning of
section "Symbols/Function Pointers"


>  Symbols/Function Pointers
>  =========================
>
>  ::
>
>         %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)
>          %pB     prev_fn_of_versatile_init+0x88/0x88
>
>  The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic
>  format. They result in the symbol name with (``S``) or without (``s``)
>  offsets. If KALLSYMS are disabled then the symbol address is printed instead.
>
>  Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``)
>  and thus deprecated. We have ``F`` and ``f`` because on ia64, ppc64 and
>  parisc64 function pointers are indirect and, in fact, are function
>  descriptors, which require additional dereferencing before we can lookup
>  the symbol. As of now, ``S`` and ``s`` perform dereferencing on those
>  platforms (when needed), so ``F`` and ``f`` exist for compatibility
>  reasons only.
>
>  The ``B`` specifier results in the symbol name with offsets and should be
>  used when printing stack backtraces. The specifier takes into
>  consideration the effect of compiler optimisations which may occur
>  when tail-call``s are used and marked with the noreturn GCC attribute.

I can return Examples back. don't really have a strong opinion
on this. let me know.

	-ss