linux-kernel - Re: [PATCH 4/5 ver2] rt2x00: Compiler warning unmasked by fix of BUILD_BUG

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Date:	Mon, 01 Sep 2008 18:17:14 +0300
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Ivo Van Doorn <ivdoorn@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Rusty Russell <rusty@...tcorp.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	"John W. Linville" <linville@...driver.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Beulich <jbeulich@...ell.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5 ver2] rt2x00: Compiler warning unmasked by fix of
 BUILD_BUG_ON

Ivo Van Doorn wrote:
> On Mon, Sep 1, 2008 at 3:44 PM, Boaz Harrosh <bharrosh@...asas.com> wrote:
>> A "Set" of a sign-bit in an "&" operation causes a compiler warning.
>> Make calculations unsigned.
>>
>> [ The warning was masked by the use of (void)() cast in the old
>>  BUILD_BUG_ON() ]
>>
>> Signed-off-by: Boaz Harrosh <bharrosh@...asas.com>
>> TO: Ivo van Doorn <IvDoorn@...il.com>
>> TO: John W. Linville <linville@...driver.com>
>> CC: Ingo Molnar <mingo@...e.hu>
>> CC: Rusty Russell <rusty@...tcorp.com.au>
>> ---
>>  drivers/net/wireless/rt2x00/rt2x00reg.h |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/wireless/rt2x00/rt2x00reg.h b/drivers/net/wireless/rt2x00/rt2x00reg.h
>> index 7e88ce5..e71b793 100644
>> --- a/drivers/net/wireless/rt2x00/rt2x00reg.h
>> +++ b/drivers/net/wireless/rt2x00/rt2x00reg.h
>> @@ -136,8 +136,8 @@ struct rt2x00_field32 {
>>  */
>>  #define is_power_of_two(x)     ( !((x) & ((x)-1)) )
>>  #define low_bit_mask(x)                ( ((x)-1) & ~(x) )
>> -#define is_valid_mask(x)       is_power_of_two(1 + (x) + low_bit_mask(x))
>> -
>> +#define is_valid_mask(x)       is_power_of_two(1 + (x) + \
>> +                                       low_bit_mask((unsigned long)x))
> 
> I know I typed it wrong, but you are missing the unsigned long cast for the
> is_power_of_two argument here (Which could also be done in the
> is_valid_mask() definition).
> 

I thought you suggested that on purpose. Since at the end it is all
one expression, the compiler propagates the cast to all participants.

Do you want that I send a fix for readability's sake?

>>  /*
>>  * Macro's to find first set bit in a variable.
>>  * These macro's behaves the same as the __ffs() function with
>> --
>> 1.5.6.rc1.5.gadf6
>>

Is below what you mean? but if so then perhaps my original one is
clearer. Note that it compiles and works as is.

---
diff --git a/drivers/net/wireless/rt2x00/rt2x00reg.h b/drivers/net/wireless/rt2x00/rt2x00reg.h
index 7e88ce5..e71b793 100644
--- a/drivers/net/wireless/rt2x00/rt2x00reg.h
+++ b/drivers/net/wireless/rt2x00/rt2x00reg.h
@@ -136,8 +136,8 @@ struct rt2x00_field32 {
  */
 #define is_power_of_two(x)	( !((x) & ((x)-1)) )
 #define low_bit_mask(x)		( ((x)-1) & ~(x) )
-#define is_valid_mask(x)	is_power_of_two(1 + (x) + low_bit_mask(x))
-
+#define is_valid_mask(x)	is_power_of_two(1LU + (unsigned long)(x) + \
+					low_bit_mask((unsigned long)x))
 /*
  * Macro's to find first set bit in a variable.
  * These macro's behaves the same as the __ffs() function with
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