linux-kernel - Re: [PATCH -tip 1/2] x86/alternatives: Fix build warning

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Date:	Fri, 05 Feb 2010 11:52:37 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip 1/2] x86/alternatives: Fix build warning

Ingo Molnar wrote:
> 
> * Masami Hiramatsu <mhiramat@...hat.com> wrote:
> 
>> Fixes below warnings.
>>
>> ====
>> FYI, there's this new build warning on x86 defconfig:
>>
>> arch/x86/kernel/alternative.c: In function 'alternatives_text_reserved':
>> arch/x86/kernel/alternative.c:402: warning: comparison of distinct pointer types lacks a cast
>> arch/x86/kernel/alternative.c:402: warning: comparison of distinct pointer types lacks a cast
>> arch/x86/kernel/alternative.c:405: warning: comparison of distinct pointer types lacks a cast
>> arch/x86/kernel/alternative.c:405: warning: comparison of distinct pointer types lacks a cast
>>
>> Caused by:
>>
>> 2cfa197: ftrace/alternatives: Introducing *_text_reserved functions
>> ====
>>
>> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
>> Reported-by: Ingo Molnar <mingo@...e.hu>
>> ---
>>
>>  arch/x86/kernel/alternative.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
>> index 3832fdc..99d9920 100644
>> --- a/arch/x86/kernel/alternative.c
>> +++ b/arch/x86/kernel/alternative.c
>> @@ -399,10 +399,10 @@ int alternatives_text_reserved(void *start, void *end)
>>  	u8 **ptr;
>>  
>>  	list_for_each_entry(mod, &smp_alt_modules, next) {
>> -		if (mod->text > end || mod->text_end < start)
>> +		if (mod->text > (u8 *)end || mod->text_end < (u8 *)start)
>>  			continue;
>>  		for (ptr = mod->locks; ptr < mod->locks_end; ptr++)
>> -			if (start <= *ptr && end >= *ptr)
>> +			if ((u8 *)start <= *ptr && (u8 *)end >= *ptr)
>>  				return 1;
>>  	}
> 
> Such casts are a bit ugly and in general type casts are somewhat dangerous.

I doubt this type casting is dangerous..., but yeah, it's ugly :-)

> One possible solution would be to add intermediary local variables 
> (text_start/text_end) with u8 * type and assign start/end to them - which can 
> be done without a cast.

Sure, I'll update it.

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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