linux-kernel - Re: [PATCH V3] kallsyms, tracing: output more proper symbol name

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Date:	Fri, 13 Mar 2009 19:25:54 +0000
From:	Paulo Marques <pmarques@...popie.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
CC:	Ingo Molnar <mingo@...e.hu>, Sam Ravnborg <sam@...nborg.org>,
	Andrew Morton <akpm@...l.org>,
	Steven Rostedt <srostedt@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3] kallsyms, tracing: output more proper symbol name

Lai Jiangshan wrote:
> [...]
> [resend, previous v3 has some mistakes]
> 
> Subject:  kallsyms, tracing: output more proper symbol name
> 
> Impact: bugfix, output reliable result
> 
> Debug tools(dump_stack(), ftrace...) are like to print out symbols.
> But it is always print out the first aliased symbol.(Aliased symbols
> are symbols with the same address), and the first aliased symbol is
> sometime not proper.
> [...]
> Aliased symbols mostly come from linker script. The solution is
> guessing "is this symbol defined in linker script", the symbols
> defined in linker script will not become the first aliased symbol.
> 
> And if symbols are found to be equal in this "linker script provided"
> criteria, symbols are sorted by the number of prefix underscores.
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> [...]
> +static int prefix_underscores_count(const char *str)
> +{
> +	const char *tail = str;
> +
> +	while (*tail == '_')
> +		tail++;
> +
> +	return tail - str;
> +}
> +
>  static int compare_symbols(const void *a, const void *b)
>  {
>  	const struct sym_entry *sa;
> @@ -521,6 +566,18 @@ static int compare_symbols(const void *a, const void *b)
>  	if (wa != wb)
>  		return wa - wb;
>  
> +	/* sort by "linker script provide" type */
> +	wa = may_be_linker_script_provide_symbol(sa);
> +	wb = may_be_linker_script_provide_symbol(sb);
> +	if (wa != wb)
> +		return wa - wb;
> +
> +	/* sort by the number of prefix underscores */
> +	wa = prefix_underscores_count((const char *)sa->sym + 1);
> +	wb = prefix_underscores_count((const char *)sb->sym + 1);
> +	if (wa != wb)
> +		return wa - wb;
> +
>  	/* sort by initial order, so that other symbols are left undisturbed */
>  	return sa->start_pos - sb->start_pos;
>  }

The code seems fine. I have no time to compile and test it right now,
but there are no obvious problems as far as I can see.

Reviewed-by: Paulo Marques <pmarques@...popie.com>

-- 
Paulo Marques - www.grupopie.com

"Measure with laser, mark with chalk, cut with chainsaw."
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