linux-kernel - Re: [PATCH 1/3] [PATCH 1/3] vsprintf: add %ps that is the same as %pS but is like %pf

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Date:	Thu, 17 Sep 2009 14:07:21 +0800
From:	Zhaolei <zhaolei@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 1/3] [PATCH 1/3] vsprintf: add %ps that is the same as
 %pS but is like %pf

Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> On PowerPC64 function pointers do not point directly at the functions,
> but instead point to pointers to the functions. The output of %pF expects
> to point to a pointer to the function, whereas %pS will show the function
> itself.
> 
> mcount returns the direct pointer to the function and not the pointer to
> the pointer. Thus %pS must be used to show this. The function tracer
> requires printing of the functions without offsets and uses the %pf
> instead.
> 
>  %pF produces run_local_timers+0x4/0x1f
>  %pf produces just run_local_timers
> 
> For PowerPC64, we need to use the direct pointer, and we only have
> %pS which will produce .run_local_timers+0x4/0x1f
> 
> This patch creates a %ps that matches the %pf as %pS matches %pF.
> 
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Zhao Lei <zhaolei@...fujitsu.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  lib/vsprintf.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 756ccaf..c265e75 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -580,7 +580,7 @@ static char *symbol_string(char *buf, char *end, void *ptr,
>  	unsigned long value = (unsigned long) ptr;
>  #ifdef CONFIG_KALLSYMS
>  	char sym[KSYM_SYMBOL_LEN];
> -	if (ext != 'f')
> +	if (ext != 'f' && ext != 's')
>  		sprint_symbol(sym, value);
>  	else
>  		kallsyms_lookup(value, NULL, NULL, NULL, sym);
> @@ -721,6 +721,7 @@ static char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  	case 'F':
>  	case 'f':
>  		ptr = dereference_function_descriptor(ptr);
> +	case 's':
>  		/* Fallthrough */
>  	case 'S':
>  		return symbol_string(buf, end, ptr, spec, *fmt);
> @@ -958,7 +959,8 @@ qualifier:
>   * @args: Arguments for the format string
>   *
>   * This function follows C99 vsnprintf, but has some extensions:
> - * %pS output the name of a text symbol
> + * %pS output the name of a text symbol with offset
> + * %ps output the name of a text symbol without offset

Comments of bstr_printf() also need to be updated.
or remove duplation and just say "refer to vsnprintf()" in bstr_printf()'s
comment.

Thanks
Zhaolei

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