linux-kernel - Re: [PATCH] vsprintf: introduce %pf

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Date:	Wed, 15 Apr 2009 17:26:33 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Zhaolei <zhaolei@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] vsprintf: introduce %pf

On Wed, Apr 15, 2009 at 09:57:54AM +0800, Zhaolei wrote:
> Frederic Weisbecker wrote:
> > If I remember well, a format which could let us to print a pure
> > function name has been suggested by Andrew Morton some monthes ago.
> > 
> > The current %pF is very convenient to print a function symbol, but
> > often we only want to print the name of the function, without
> > its asm offset.
> > 
> > That's what does %pf in this patch.
> > The lowecase f has been chosen for its intuitive sense of a weak kind
> > of %pF
> > 
> > The support for this new format would be welcome for the tracing tree
> > where the need to print pure function names is often needed and also
> > on other parts:
> > 
> > $ git-grep -E "kallsyms_lookup\(.+?\)"
> > arch/blackfin/kernel/traps.c:   symname = kallsyms_lookup(address, &symsize, &offset, &modname, namebuf);
> > arch/powerpc/xmon/xmon.c:               name = kallsyms_lookup(pc, &size, &offset, NULL, tmpstr);
> > arch/sh/kernel/cpu/sh5/unwind.c:        sym = kallsyms_lookup(pc, NULL, &offset, NULL, namebuf);
> > arch/x86/kernel/ftrace.c:       kallsyms_lookup((unsigned long) syscall, NULL, NULL, NULL, str);
> > kernel/kprobes.c:               sym = kallsyms_lookup((unsigned long)p->addr, NULL,
> > kernel/lockdep.c:       return kallsyms_lookup((unsigned long)key, NULL, NULL, NULL, str);
> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> > kernel/trace/ftrace.c:  kallsyms_lookup((unsigned long)rec->ops->func, NULL, NULL, NULL, str);
> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, &modname, str);
> > kernel/trace/ftrace.c:  kallsyms_lookup(*ptr, NULL, NULL, NULL, str);
> > kernel/trace/trace_functions.c: kallsyms_lookup(ip, NULL, NULL, NULL, str);
> > kernel/trace/trace_output.c:    kallsyms_lookup(address, NULL, NULL, NULL, str);
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> >  lib/vsprintf.c |   13 +++++++++----
> >  1 files changed, 9 insertions(+), 4 deletions(-)
> > 
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index b56f6d0..15c9094 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -575,12 +575,15 @@ static char *string(char *buf, char *end, char *s, struct printf_spec spec)
> >  }
> >  
> >  static char *symbol_string(char *buf, char *end, void *ptr,
> > -				struct printf_spec spec)
> > +				struct printf_spec spec, char ext)
> >  {
> >  	unsigned long value = (unsigned long) ptr;
> >  #ifdef CONFIG_KALLSYMS
> >  	char sym[KSYM_SYMBOL_LEN];
> > -	sprint_symbol(sym, value);
> > +	if (ext != 'f')
> > +		sprint_symbol(sym, value);
> > +	else
> > +		kallsyms_lookup(value, NULL, NULL, NULL, sym);
> >  	return string(buf, end, sym, spec);
> >  #else
> >  	spec.field_width = 2*sizeof(void *);
> > @@ -692,7 +695,8 @@ static char *ip4_addr_string(char *buf, char *end, u8 *addr,
> >   *
> >   * Right now we handle:
> >   *
> > - * - 'F' For symbolic function descriptor pointers
> > + * - 'F' For symbolic function descriptor pointers with asm offset
> > + * - 'f' For simple function symbol
> Hello, Frederic
> 
> Good patch.
> 
> But is it necessary to add some explain of '%pf' in bstr_printf() and
> vsnprintf() as:
>   /*
>    ...
>    * %pS output the name of a text symbol
> -  * %pF output the name of a function pointer
> +  * %pf output the name of a function pointer
> +  * %pF output the name of a function pointer with asm offset
>    * %pR output the address range in a struct resource
>    ...
>    */
> For programmers tend to find manual in comment of vsnprintf() instead of
> pointer().


Ah indeed!
I will update the patch with your comment.

Thanks,
Frederic.


> Thanks
> Zhaolei
> 
> >   * - 'S' For symbolic direct pointers
> >   * - 'R' For a struct resource pointer, it prints the range of
> >   *       addresses (not the name nor the flags)
> > @@ -715,10 +719,11 @@ static char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> >  
> >  	switch (*fmt) {
> >  	case 'F':
> > +	case 'f':
> >  		ptr = dereference_function_descriptor(ptr);
> >  		/* Fallthrough */
> >  	case 'S':
> > -		return symbol_string(buf, end, ptr, spec);
> > +		return symbol_string(buf, end, ptr, spec, *fmt);
> >  	case 'R':
> >  		return resource_string(buf, end, ptr, spec);
> >  	case 'm':
> 
> 

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