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

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Date:	Wed, 11 Mar 2009 13:05:19 +0000
From:	Paulo Marques <pmarques@...popie.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Lai Jiangshan <laijs@...fujitsu.com>,
	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] kallsyms, tracing: output more proper symbol name

Ingo Molnar wrote:
> * Lai Jiangshan <laijs@...fujitsu.com> wrote:
> 
>> +#define VMLINUX_SYMBOL(_sym_) #_sym_
>> +
>> +static const char *hide_symbols[] = {
>> +	/* misc symbols */
>> +	"_text",
>> +	"_stext",
>> +	"_etext",
>> +	"_sinittext",
>> +	"_einittext",
>> +
>> +	/* symbols from include/asm-generic/vmlinux.lds.h */
>> +	VMLINUX_SYMBOL(__start_mcount_loc),
>> +	VMLINUX_SYMBOL(__stop_mcount_loc),
[...]
>> +	VMLINUX_SYMBOL(__early_initcall_end),
>> +	VMLINUX_SYMBOL(__per_cpu_start),
>> +	VMLINUX_SYMBOL(__per_cpu_end)
>> +};
> 
> I like how you try to solve this at symbol table generation 
> time.

Yes, this is the proper way to do it.

> Instead of this hardcoded table, couldnt we use some more 
> flexible and more future-proof method? Such as ordering 
> same-address symbols by underscores:
> 
>   [same address]
> 
>   non-underscore symbols first        XYZ
>   single-undescroe symbols second     _XYZ
>   double-underscore symbols third     __XYZ
> 
> that way the scheme would be more or less self-maintaining as an 
> underscore already carries a "this is a special, internal 
> symbol" notion.

I agree with this approach, but to be on the side we should skim through
the alias and see if this works for most symbols or not.

I just did this for the symbols on my running kernel and it seems to
work. The hierarchy for '_' and '__' is in fact necessary:

> ffffffff80447418 T __sched_text_start
> ffffffff80447418 t sleep_on_common
> ffffffff80449830 T __lock_text_start
> ffffffff80449830 T __sched_text_end
> ffffffff80449830 T _spin_trylock
> ffffffff80453d50 R __stop___ex_table
> ffffffff80453d50 T __start_notes
> ffffffff8045b000 R __start_rodata
> ffffffff8045b000 R linux_banner

or that "_spin_trylock" might be displayed incorrectly as
"__sched_text_end" or something like that.

-- 
Paulo Marques - www.grupopie.com

"Who is general Failure and why is he reading my disk?"
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