linux-kernel - Re: RFC: introduce struct ksymbol

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Message-ID: <84144f020904142313m4da323fdj9a8becf3010c519c@mail.gmail.com>
Date:	Wed, 15 Apr 2009 09:13:12 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Joe Perches <joe@...ches.com>, Sam Ravnborg <sam@...nborg.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: RFC: introduce struct ksymbol

Hi Ingo,

On Wed, Apr 15, 2009 at 8:58 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> (Sam and Rusty Cc:-ed)
>
> * Joe Perches <joe@...ches.com> wrote:
>
>> On Wed, 2009-04-15 at 02:00 +0200, Frederic Weisbecker wrote:
>> > 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);
>>
>> Perhaps a conversion from
>>
>> "char str[KSYM_SYMBOL_LEN]"
>> to
>> "struct ksymbol sym"?
>>
>> could be useful.
>>
>> There are a few places that use a hard coded length of 128
>> instead of KSYM_SYMBOL_LENGTH that are also converted.
>>
>> Compile tested only
>
> Why not 'struct ksym'? That name is unused right now, it is shorter
> and just as descriptive.
>
> Regarding the change... dunno. Sam, Rusty - what do you think?
>
> Downsides would be loss of awareness of stack footprint impact. A
> plain struct is easy to slap on, and it's not immediately visible
> that it carries 128 bytes of weight. It might also be confusing in
> terms of the nature of the interface - whether it's a pointery
> object or not.
>
> Prior use:
>
>        char str[KSYM_SYMBOL_LEN];
>
>        kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
>
> New use:
>
>        struct ksym sym;
>
>        kallsyms_lookup(rec->ip, NULL, NULL, NULL, &sym);
>
> Dunno.

The change makes sense to me. Passing a raw char pointer down the
call-chain is a buffer overflow waiting to happen and as a matter of
fact, we've had bugs in this area before. See commit
9c24624727f6d6c460e45762a408ca5f5b9b8ef2 ("KSYM_SYMBOL_LEN fixes") for
an example.

                                      Pekka
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