linux-kernel - Re: [RFC][PATCH v2 6/7] symbol lookup: use new kernel and module dereference functions

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Message-ID: <20170921093808.GE773@jagdpanzerIV.localdomain>
Date:   Thu, 21 Sep 2017 18:38:08 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        James Bottomley <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH v2 6/7] symbol lookup: use new kernel and module
 dereference functions

On (09/21/17 01:29), Sergey Senozhatsky wrote:
[..]
> +	%pS	versatile_init+0x0/0x110
> +	%ps	versatile_init
>  	%pF	versatile_init+0x0/0x110
>  	%pf	versatile_init
> -	%pS	versatile_init+0x0/0x110
>  	%pSR	versatile_init+0x9/0x110
>  		(with __builtin_extract_return_addr() translation)
> -	%ps	versatile_init
>  	%pB	prev_fn_of_versatile_init+0x88/0x88
>  
> -The ``F`` and ``f`` specifiers are for printing function pointers,
> -for example, f->func, &gettimeofday. They have the same result as
> -``S`` and ``s`` specifiers. But they do an extra conversion on
> -ia64, ppc64 and parisc64 architectures where the function pointers
> -are actually function descriptors.
> -
>  The ``S`` and ``s`` specifiers can be used for printing symbols
>  from direct addresses, for example, __builtin_return_address(0),
>  (void *)regs->ip. 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.

JFI,

I have updated this part. it's probably too early to completely
wipe out pF/pf info.

the updated Doc goes like this:

+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.

	-ss